INVESTIGATING THE EFFECTS OF PRECOOLING ON RECREATIONALLY
ACTIVE INDIVIDUALS DURING A LOADED CARRIAGE FOOT MARCH IN
HEATED CONDITIONS

By

Christopher A. Esposito, B.S.
East Stroudsburg University of Pennsylvania

A Thesis Submitted in Partial Fulfillment of
the Requirements for the Degree of Master of Science in Exercise Science
to the office of Graduate and Extended Studies of
East Stroudsburg University of Pennsylvania

August 9, 2019

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ABSTRACT
A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master
of Science in Exercise Science to the office of Graduate and Extended Studies of East
Stroudsburg University of Pennsylvania
Students Name: Christopher A. Esposito
Title: Investigating the effects of precooling on recreationally active individuals during a
loaded carriage foot march in heated conditions
Date of Graduation: August 9, 2019
Thesis Chair: Chad Witmer, Ph.D.
Thesis Member: Gavin Moir, Ph.D.
Thesis Member: Matthew Miltenberger, Ph.D.

Abstract
Introduction: Over the past 20 years, the literature has demonstrated that military
members are prone to exertional heat illness due to a combination of heavy loads and
physical exertion. Precooling is a relatively new idea where an individual ingests a
substance preemptively to lower core temperature before an activity. Purpose: The aim
of this study was to investigate the effects of a precooling protocol employing ice slurry
(0±1°C) vs. cold water (4°C) on core body temperature and time to exhaustion during a
simulated military full combat gear foot march in males aged 18 to 35 years.
Methodology: The researchers used a precooling protocol of 7.5g/kg of bodyweight of
both water (control) and ice-slurry (experimental) administered over a 30-minute period.
Following the precooling protocol, the participants self-selected a pace from 3.0-4.0
MPH and walked for up to 90 minutes or until volitional fatigue inside a heat tent while
wearing full Army combat gear. Core temperature, heart rate and RPE were collected
every 5 minutes. Blood pressure was collected pre and post exercise. Results: There was
no difference in time to exhaustion (p = 0.227), heart rate (p = 0.763) or core temperature
(p = 0.876) between conditions. Conclusion: Precooling protocol was ineffective at
lowering core temperature vs. control and thus did not increase time to exhaustion.
Additional research on precooling with military equipment is needed to further elucidate
the potential benefits of precooling on exercise performance and decreasing the risk of
exertional heat illness.

TABLE OF CONTENTS
List of Figures

vi

List of Tables

vii

CHAPTER 1: INTRODUCTION

1

Purpose

5

Null Hypotheses

5

Delimitations

5

Limitations

6

Operational Definitions

6

Summary

7

CHAPTER 2: LITERATURE REVIEW

8

Thermoregulation

8

Effect of Heat Physiology on Performance

9

Exertional Heat Illness

11

Different Cooling Methods

13

Fluid Replacement

18

Balancing Protection and Health

19

CHAPTER 3: METHODOLOGY

22

Participants

22

Participant Characteristics

22

Inclusion and Pre-Participation Requirements

23

Hydration Status

24

Hydration and Pre-Conditions

24

Precooling Protocol

25

Experimental Conditions

26

Experimental Design

26

Absolute Test Termination Criteria

29

Statistical Analysis

30
iv

CHAPTER 4: RESULTS

31

Kinetic Results

31

Metabolic and Physiological Results

33

Smallest Worthwhile Change

36

CHAPTER 5: DISCUSSION & CONCLUSION

40

Precooling Protocol and Statistics

40

Physiological Strain Index

43

Core Temperature End Point

44

Future Considerations

44

Implications

46

Conclusion

47

REFERENCES

48

APPENDICES

56

APPENDIX A: Institutional Review Board Approval

56

APPENDIX B: Informed Consent for Scientific Study

57

APPENDIX C: Physical Activity Readiness Questionnaire (PAR-Q) and You

60

v

LIST OF FIGURES
Figure 1. Mean time to exhaustion per participant by condition

32

Figure 2. Mean core temperature per participant by condition

34

Figure 3. Mean heart rate per participant by condition

35

Figure 4. Physiological strain index for all participants for both conditions

36

Figure 5. Time to exhaustion for three participants in both trials

37

Figure 6. Core temperature values separated by condition at different time intervals for
Participant 1
38
Figure 7. Core temperature values separated by condition at different time intervals for
Participant 4
38
Figure 8. Figure 10. Core temperature values separated by condition at different time
intervals for Participant 5

vi

39

LIST OF TABLES
Table 1. Subject Characteristics

23

Table 2. List of lower extremity injuries that would exclude subject participation

24

Table 3. Mean (SD) Values for both conditions of all subjects per variable

32

vii

CHAPTER 1: INTRODUCTION
Load Carriage foot marches are a routine aspect of training and combat operations for
both new recruits and veterans among different military disciplines. Soldiers are required
to carry loads that range from 35 pounds to 50 pounds on marches that can span from a
few to many miles (Smith, S., 2019). Since the 1980s, there have been over 5,000
documented cases of military members having heat related injuries (Carter et al., 2005),
with most cases of exertional heat illnesses coming from both hot environments (33.5%)
and temperate environments (34.6%) (Stacey et al., 2015).
Many of the heat illness cases impacted gun crewmen and infantry soldiers, two units
which regularly engage in loaded carriage foot marches (Carter et al., 2005). Infantry
men and gun crewmen typically aid in the mobilization of troops and execute
reconnaissance missions while carrying increased loads (Smith, S., 2019; Infantryman
((11B), (2019)). Exertional heat illnesses are serious and pose a major threat to trainees’
health status as they endure long treks on these loaded foot marches, especially in the
heat. Increasing the carrying capacity load by wearing a pack and holding extra gear
while going on long treks in the heat may further increase the risk of heat illnesses.
Recently, there have been
1

efforts to try and prevent exertional heat illnesses using pre-cooling protocols to
reduce core temperature prior to physical activity.
There is evidence within the literature suggesting that the magnitude of heat can
affect physiological responses within the human body (Hayes et al., 2014). In most cases
heart rate will increase with heat exposure secondary to a decreased blood pressure due to
a reduction in plasma volume induced by sweating (Cheung, S. S., 2010). If the exposure
to the heat persists, it can lead to decreased exercise performance; this decrease in
exercise performance capability is believed to be directly correlated to a mechanism in
the body which signals the body to cease exercise before any thermal damage can be
done (Cheung, S. S., 2010; Cheung, S. S., & McLellan, T. M., 1998; Gonzalez-Alonso et
al., 1999). This mechanism is believed to occur once a certain core temperature set point
has been reached, at which point; the body is signaled to shut down and the individual
fatigues (Cheung, S. S., 2010). The shutdown that Cheung refers to is just the
individual’s will to cease exercise during the test and was characterized as the individual
being heavily fatigued (Cheung, S. S., 2010). For highly fit individuals the marker is
approximately 39.2°C, and for moderately fit the marker is approximately 38.8°C.
Interestingly, the systemic shut down referred to by Cheung (2010) does not appear to
have any long-lasting negative effects as data has demonstrated no ill effects up to 24
hours post-even in either animals or human; this suggests exhaustion occurred well
before any health complications and any system failure (Cheung, S. S., 2010). The safety
switch can be an issue for a military member however, if an individual cannot keep up
with the rest of the unit; then the entire unit is slowed potentially risking the success of a
mission.

2

Past literature has focused on cooling measures that are employed either during or
post-exercise in relation to loaded foot marches (Nye et al., 2017). One such protocol is
known as cold water immersion. Cold water immersion is when an individual sits in a tub
filled with either cold water, ice or a mixture of the two to lower core temperature. This
has been demonstrated to be effective in lowering heat strain post-exercise (Nye et al.,
2017). Another method is known as icy sheets, where long thin ice packs are placed on
the neck, head, groin and each arm pit. There is very limited research on icy sheets and it
only acts to cool after exposure to the heat and or exercise (Nye et al., 2017). Nye and his
team have also demonstrated that icy sheets are an ineffective method at cooling (Nye et
al., 2017). Other researchers have also investigated ventilated vests which enhance
convective cooling (Chinevere et al., 2008; Hadid et al., 2008). The vests incorporate an
impermeable outer layer and have an ambient air blower that uses air as a convective way
to cool the torso (Chinevere et al., 2008). The vest is worn under any and all equipment,
it is also lightweight to minimize the additional load to the individual (Chinevere et al.,
2008). Both Chinevere’s (2008) team and Hadid’s (2008) research has shown the cooling
vests to be effective in lowering core temperature. An issue regarding post-exercise
cooling interventions is that individuals are put at risk before heat stress is addressed.
The most recent applicable method that has been effective in lowering core
temperature is precooling. Precooling is a useful strategy for combating the detrimental
effects that heat stress has on exercise performance, and involves utilizing different
mechanisms (ingestion, conductive or convective cooling) to preemptively reduce core
body temperature prior to exercise (Jones et al., 2012; Pryor et al., 2014; Walker et al.,
2014; Siegel et al., 2010; Zimmerman et al., 2015). Precooling is done so that core

3

temperature is pre-emptively lowered in order to raise the heat storage capacity of an
individual (Siegel et al., 2010). Heat storage capacity is the amount of thermal energy
being stored in the body, and by lowering core temperature, the body has an increased
heat storage capacity of an individual to be capable of holding more thermal energy
(Siegel et al., 2010). Pre-cooling is typically done prior to exercise in smaller intervals
(i.e. breaking down a 30-minute period of precooling into 6, 5-minute periods of
precooling). One of the more recent precooling trends has been the use of an ice slurry.
Multiple researchers have demonstrated that ice slurry and crushed ice ingestion
have significantly lowered core temperature both pre and during exercise (Jones et al.,
2012; Pryor et al., 2014; Walker et al., 2014; Siegel et al., 2010; Zimmerman et al.,
2015). However, there are still pieces of information missing, such as ingestion time and
dose. There are different prescriptions of quantity, though most of the research suggests
either 7.0 g/kg or 7.5g/kg of body weight; typically ingested over a 30-minute duration by
drinking roughly 1.16 g/kg or 1.25g/kg of substance every 5 minutes (Siegel et al., 2010;
Walker et al., 2014). The use of an ice-slurry is highly practical because it can be
administered to many people and is relatively low cost. There has been ample research
that shows pre-cooling is effective at lowering core temperature and thereby increasing
the heat storage capacity of an individual (Jones et al., 2016; Pryor et al., 2014; Walker et
al., 2014; Siegel et al., 2010; Zimmerman et al., 2015). Pre-cooling seems to have
applicability to military foot marches because of its effectiveness and relatively low
levels of cost.
In terms of using pre-cooling in relation to load carriage foot marches, there
seems to be limited research. To the investigators’ current knowledge, there was no study
4

outlining the possible effects of using a pre-cooling method for load carriage foot
marches. Pre-cooling offers a cost-effective method at reducing core temperature.
Applying precooling to load carriage foot marches may offer a possible solution where
there is a need to help reduce exertional heat illnesses and improve exercise performance
in hot conditions.
Purpose
The aim of this study was to investigate the effects of a precooling protocol
employing ice slurry (0±1°C) vs. cold water (4°C) on core body temperature and time to
exhaustion during a simulated military full combat foot marches in males aged 18 to 35.
Null Hypotheses
There will be no statistically significant difference between the precooling
protocol and the control on core body temperature while wearing full combat gear.
There will be no statistically significant difference in time to exhaustion between
the experimental trial and control protocol while doing the load carriage foot marches.
Delimitations
1) Participants were recreationally active individuals from a University in
Northeastern Pennsylvania.
2) Participants were males aged from 18-35 years.
3) Participants were physically active at least three times per week following ACSM
guidelines (20-60 minutes of activity) 3-5 times per week (Garber et al., 2011).
4) Participants were apparently healthy with no prior history of heat illness injuries.

5

5) Participants were apparently healthy with no lower extremity injuries in the past
year.
Limitations
1) Participant dropout due to illness or injury.
2) Participants level of heat acclimatization.
3) Participants adherence to pre-conditions.
4) Participants were giving maximal effort.
5) Failure to replicate pre-exercise 24-hour diet.

Operational Definitions
Combat Gear – Combat uniform, summer weight boots, a Fighting Load Carrier
(FLC) vest, ruck sack (35lbs), and Army Combat Helmet. (ACH).
Army Combat Uniform Pattern – Army combat uniform (ACU), standard battle
uniforms worn by the United States Army.
Operational Camouflage Pattern – Operational Camouflage Pattern (OCP), the United
States Army main camouflage pattern on uniforms.
Foot March – Walking treadmill test where participants chose a speed ranging from
3.0-4.0 MPH and 0% grade for 90 minutes or until volitional fatigue.
Hot Conditions – A tent heated to and maintained at 33 degrees Celsius with
individual heating units (Zimmerman et al., 2015).
Recreationally Active – Following ACSM guidelines, 20-60 minutes per day for at
least 3-5 times per week (Garber et al., 2011).
6

Summary
Load Carriage foot marches are an integral part of military training. However, over
the last 20 years, different forms of heat illnesses have been plaguing cadets which
hinders both health and performance (Carter et al., 2005). Military branches have
employed countermeasures but most of these are not used due to cost or have been
demonstrated as ineffective in lowering core temperature and therefore preventing heat
illnesses (Nye et al., 2017). The task at hand was to identify a cost-effective method
which could lower core temperature in hot conditions in order to reduce the chance of
heat illnesses and improve exercise performance for military members.

7

CHAPTER 2: LITERATURE REVIEW
Thermoregulation
Regulation and effector responses to thermoregulatory issues are strongly
influenced by the hypothalamus, specifically a region known as the preoptic area
(Cheung, S. S. 2010; Nagashima, K., 2015). There are thermos-sensitive neurons (TSN)
in this preoptic area that are sensitive to any type of thermoregulation variance, whether it
be hot or cold stimulation. The TSN are also distributed in the skin and other areas of the
brain and is mostly regulated by the central nervous system; however, the TSN and
thermoregulatory system is currently not fully understood (Cheung, S. S. 2010;
Nagashima, K., 2015). There are different theories on how thermoregulation works but it
is surmised that the autonomic responses due to the potential variance in core body
temperature and skin temperature are from this preoptic area in the hypothalamus
(Cheung, S. S. 2010).
A few autonomic responses that occur due to cold exposure in humans is that the
superficial subcutaneous arterial vessels will constrict; this will limit blood flow to the
skin so that heat loss will be minimalized (Cheung, S. S. 2010; Nagashima, K., 2015).
8

The body will also start to generate heat via shivering thermogenesis and non-shivering
thermogenesis (Cheung, S. S. 2010; Nagashima, K., 2015). The former generating heat
by repeatedly contracting the muscles, while the latter increases metabolic activity in
brown-adipose via uncoupling of oxidative phosphorylation to increase heat production
(Nagashima, K., 2015).
The autonomic responses that occur due to heat exposure is different from that of
a response to a cold environment. The vessels will dilate so that blood can flow from the
core to the skin freely to try and release heat from the body via either convective or
conductive measures (Nagashima, K., 2015). The human body will also sweat, in hopes
to alleviate heat via evaporative means (Nagashima, K., 2015).
Effect of Heat Physiology on Performance
There are three separate studies that have looked for a temperature endpoint that
is associated with volitional fatigue and a request to stop exercise by the participants. In
Cheung and McLellan’s study done in 1998, there were four conditions: euhydrated and
pre-acclimation, euhydrated and post-acclimation, hypohydrated and pre-acclimation, and
hypohydrated and post-acclimation (Cheung, S. S., & McLellan, T. M., 1998). For
moderately fit individuals, they found the cut-off point for core body temperature and
volitional fatigue to be 38.8°C (0.3), 38.8°C (0.3), 38.7°C (0.3) and 38.6°C (0.3)
respectively (the numbers in parentheses represents the standard error) (Cheung, S. S., &
McLellan, T. M., 1998). For highly fit individuals they found it to be 39.2°C (0.2),
39.1°C (0.2), 39.2°C (0.1) and 39.2°C (0.1) respectively (Cheung, S. S., & McLellan, T.
M., 1998).
9

One team of researchers had five conditions, which were precooled, control,
preheated, low rate of heat storage and high rate of heat storage (Gonzalez-Alonso et al.,
1999). The endpoint of core temperature for those groups were 40.1°C (0.1), 40.2°C
(0.1), 40.1°C (0.1), 40.1°C (0.3) and 40.3°C (0.3) respectively (Gonzalez-Alonso et al.,
1999). Two other researchers, Selkirk and McLellan, found similar results in 2001. They
had four conditions, two were for highly fit individuals; trained participants and low body
fat and trained participants and high body fat (Selkirk, G. A., & McLellan, T. M., 2001).
The two conditions for moderately fit individuals were untrained participants with low
body fat and untrained participants with high body fat (Selkirk, G. A., & McLellan, T.
M., 2001). The trained participants with low body fat had an end-point core temperature
of 39.5°C (0.0) (Selkirk, G. A., & McLellan, T. M., 2001), while the trained participants
with high body fat had an end-point core temperature of 39.2°C (0.1) (Selkirk, G. A., &
McLellan, T. M., 2001). For the moderately fit group with low body fat, the end-point
core temperature was 38.6°C (0.2) (Selkirk, G. A., & McLellan, T. M., 2001). The
moderately fit group with high body fat had a core temperature end point of 38.8°C (0.2)
(Selkirk, G. A., & McLellan, T. M., 2001). These values are all very similar and are
within 1°C of another regardless of the condition, training status and body fat percentage.
Cheung theorizes that because none of the participants suffered ill effects for up to 24
hours later, that the body shuts down well before potential health risks (Cheung, S. S.
2010). It is thought that the body has an endpoint of core temperature in relation to
volitional fatigue so that system integrity and function is not predisposed to injury or
malfunction (Cheung, S. S. 2010). However, there is not enough information as to know
how this pathway works or how the signal is sent and received.
10

Exertional Heat Illness
Exertional heat illness is when the body’s thermoregulatory system becomes
compromised due to excessive heated conditions or because of too much physical
exertion; or it could arise from a combination of both (Phinney et al., 2001). There are
three classifications of exertional heat illnesses, exertional heat cramps, exertional heat
exhaustion and exertional heat stroke (Cheung, S. S. 2010). Usually, a core temperature
of 40.5°C or greater puts an individual at a greater risk to have an exertional heat illness
(Casa et al., 2015).
Exertional heat cramps are a mild form of exertional heat illness. It is the least
worrisome out of the three, however, if left untreated it could potentially progress to the
next stage and be detrimental. Heat cramps can occur without a direct increase in core
temperature (Casa et al., 2015). It is characterized by recurring cramps usually in the
lower extremity. Usually, exertional heat cramps are treatable through proper rehydration
and with recovery, or by getting out of a hot environment and into a cooler one (Cheung,
S. S., 2010).
Exertional heat exhaustion is the second stage of exertional heat illness. It is a
stage where the body can no longer work effectively (Casa et al., 2015). The result of this
could be a singular issue or a combination of multiple factors, which include
cardiovascular insufficiency, hypotension, central fatigue and energy depletion (Casa et
al., 2015). Heat exhaustion is typically characterized by having an increased core
temperature but being lower than 40.5°C (Casa et al., 2015). At this stage, the individual
could be at risk for heat syncope, organ damage (specifically renal system and possible
11

liver damage) and significant central nervous system dysfunction (Casa et al., 2015).
Some symptomology includes confusion, dizziness, headache and fatiguing (Casa et al.,
2015). Using methods such as rehydration or cold-water immersion could help an
individual reverse the symptomology of exertional heat exhaustion.
Exertional heat stroke is the last stage and most dangerous out of the three
exertional heat illness classifications. This illness is usually brought on by a combination
of metabolic heat production, environmental factors and inhibited heat loss (Casa et al.,
2015). It is characterized by a core temperature of 40.5°C and greater (Casa et al., 2015).
The first sign is usually CNS dysfunction, which could cause heat syncope, irritability,
confusion and altered consciousness (Casa et al., 2015). This can progress into multiorgan failure and possibly death if untreated (Casa et al., 2015). The risk for mortality
increases the longer the individual stays above a core temperature of 40.5°C, so getting
the individual treatment as quickly as possible is of the upmost importance (Casa et al.,
2015).
Exertional heat illness poses a serious threat to anyone who is physically active,
works in a hot environment, or has a damaged thermoregulatory system. Added loads and
equipment for work and or sports such as football or an occupation such as an active
military member can even further increase the likelihood of having an exertional heat
illness (Phinney et al., 2001: Pryor et al., 2018).

12

Different Cooling Methods
Within the literature, there are numerous methods that were used to induce a
cooling effect on the body. There were four methods of cooling investigated, cold water
immersion (CWI), icy sheets (IS), convective cooling vests (CCV) & precooling (Pc).
The first being investigated is CWI. One group of researchers recruited 18 participants (9
male & 9 female) to walk at 4mph and 0% grade on a treadmill in a heat tent for up to 90
minutes or until core temperature reached 40°C (Nye et al., 2017). Immediately after
exercise, the participant removed the military uniform and entered the CWI tank in shorts
and a top. The water was between 5-10°C. Participants were immersed in the CWI tank
until core temperature reached 37.5°C. CWI was effective in lowering core temperature
for this study design (Nye et al., 2017).
Walker et al. (2014) also looked at CWI. There were 74 total participants in their
research design, which were split into three groups: one CWI group, one control group
and one iced slush ingestion group. This study was a simulated search and rescue for
firefighter, where the participants had to perform two 20-minute simulated searches in a
40.5°C chamber. Each 20-minute search was split in half, where at the halfway point the
participants would exit the chamber, remove their jackets, and change their breathing
apparatus. This was to emulate the exact protocol that firefighters use in actual
firefighting scenarios. After the simulation was complete, the participants exited the
chamber and stripped down to shorts and entered a CWI tank which was set to 15°C. The
tank was in the shade and participants stayed in the tank for up to 15 minutes. The water
level went up to the individual’s umbilicus while their arms stayed out of the tank. Both
13

the crushed ice ingestion and CWI were effective in returning core temperature back to
baseline values within 15 minutes (Walker et al., 2014).
CWI has been demonstrated to be effective in returning core temperature back to
normal range, however there are two concerns with this method. If the individual stays
immersed for too long, the individual could be put at risk of hypothermia. The other
concern, especially in a military setting, is that it requires time and equipment. It may be
practical for trainees, but overseas or in a combat setting, time and space may not be
available. It also cannot be applied to multiple people at one time. While CWI is the gold
standard for cooling, it still has some limitations to it.
Icy sheets are a method of cooling that are used by placing ice sheets on the head,
neck, groin and each armpit. The temperature of the icy sheets are typically 5-10°C. One
group of researchers used icy sheets for individuals after walking for up to 90 minutes of
exercise at 4mph and 0% grade on a treadmill in a heat chamber (38.5±0.5°C) (Nye et al.,
2017). The participants walked to a separate room and stripped to shorts and a top. The
ice sheets were placed on the participants on the head, neck, groin and each armpit. The
sheets were replaced every three minutes to ensure the cooling temperature of 5-10°C
was maintained. The cooling protocol used was the same as CWI where the cooling
method was continued until normal core temperature was reached. This cooling method
was not effective in reducing core temperature to within normal limits in a reasonable
amount of time (within 15 minutes) when compared to the CWI protocol. (Nye et al.,
2017).

14

Convective cooling vests (CCV) are a relatively new method to try and cool the body
during exercise or physical activity. CCV’s are worn under any clothes or equipment
around the bare chest of the individual. It takes ambient air through a small tube and
shuttles it towards the trunk, in hopes to help evaporate heat that may be contained under
the heavy equipment being used by the individual. One team of researchers used a type of
CCV which simulated a ruck-march (Chinevere et al., 2008). The treadmill protocol was
1.34 meters per second and 0% grade to elicit a metabolic rate of ~200 watts. There were
7 participants who had 9 separate sessions. Each session was in a different environment
and the CCV had a different use. The three environments were -40°C and 20% relative
humidity, 30°C and 50% relative humidity and finally 35°C and 75% relative humidity.
The three different settings for the CCV were CCV turned on, CCV turned off, and no
CCV. What was demonstrated at the end of this design was that heart rate, core
temperature and sweating rates were significantly lower in the different environments
with the system being on versus off (Chinevere et al., 2008).
Hadid et al. (2008)looked at CCV in 2008 as well. He had 12 participants walk on a
treadmill for up to 115 minutes followed by a 70-minute recovery window. There were
two environmental conditions, 40°C and 40% relative humidity and 35°C and 60%
relative humidity. There were two conditions where the participants had a CCV equipped
or no CCV equipped. The CCV was effective in lowering core temperature and skin
temperature compared to no CCV being equipped in both environments. Heart rate was
not significantly lowered for the CCV group in both conditions. The vests were
demonstrated to be effective in lowering core temperature during exercise in heated
15

conditions (Hadid et al., 2008). There are a few limitations to the vests, however. One is
that they add weight, and when you add any extra weight to a military member who is
already carrying upwards of 40 lbs. of equipment, there can be added risk for load
bearing injuries. Another potential limitation in terms of using them with military
members is the cost of the vests. Each military member would need a vest and that could
add up in costs compared to other methods that are cheaper such as precooling with a
slurry.
Precooling is a technique to preemptively cool the body prior to exercise or certain
heated conditions (Cheung, S. S., 2010). There has been research done to support the
claims that precooling via ingestion of an ice slurry has lowered core temperature and in
turn increased an individual’s heat storage capacity (Siegel et al., 2010). However, there
is also research that demonstrates the ice-slurry ingestion increased heat storage capacity
but did not improve physical performance. (Zimmerman et al., 2015). The use of an iceslurry presents a practical and easily implemented precooling protocol at a very low cost.
It is still being used and researched as a method of precooling to try and lower core body
temperature.
One researcher used a precooling protocol that administered 7.5g/kg of bodyweight of
ice slurry over a 30-minute period (Siegel et al., 2010). There were 10 male participants
who either ingested a control cold water 4°C or an experimental 0°C ice slurry before
running a ventilatory threshold test in heated conditions (34°C) (Siegel et al., 2010).
Before exercise, core body temperature was lower in the ice slurry condition when
compared to the control (Siegel et al., 2010). Ice slurry ingestion also helped to increase
16

the duration of the submaximal running activity in the heated conditions (Siegel et al.,
2010).
One group of researchers recruited 9 moderately trained females to perform a cycling
protocol in 33°C heat (Zimmerman et al., 2015). The cycling protocol imitated games
that include a halftime such as soccer and field hockey and involved the completion of
2x36 minute halves on a cycler ergometer (18x 4 second sprints with 96 seconds of
recovery, and 5x2 second repeated spring efforts after the 8th and 16th sprint)
(Zimmerman et al., 2015). There was a control water precooling protocol and an
experimental precooling crushed ice ingestion protocol. The protocol was the same for
either condition, only the substance was different; the participants were administered
6.8g/kg of bodyweight or either crushed ice or water over a 30-minute period where they
were seated for the duration of the protocol. The crushed ice ingestion protocol did lower
core body temperature significantly before exercise compared to the control water
protocol, and it also lowered the perception of thermal stress (Zimmerman et al., 2015).
However, there was no improvement in performance with ice ingestion compared to
control (Zimmerman et al., 2015).
One group of researchers had 10 male firefighters use the same precooling ingestion
protocol as Siegel et al. (2015), (7.5g/kg of bodyweight), and had them walk on a
treadmill in 38.8°C and full fire fighter gear. There were two conditions, an experimental
precooling slurry (0.1°C) and a precooling control beverage (20°C). The researchers
collected gastric temperature, skin temperature, heart rate, perceiving of thermal
sensation, ratings of perceived exertion, comfort and sweating. The researchers found a
17

modest difference between gastric temperatures that demonstrated a slight decrease in the
ice slurry protocol however it was not statistically significant. However, the difference
did not persist for the 45-minute duration of the exercise protocol.
The precooling ice-slurry and crushed ice ingestion have been demonstrated to be
effective in lowering core temperature but need further investigation. Precooling seems to
be a reliable method to lower core temperature prior to exercise, however, it is not clear if
it will improve performance in both sports and occupational fields (fire fighters). It would
seem likely that precooling may be influenced by occupation, environment, mode of
exercise, type of precooling protocol and many other potential variables. Despite the
potential variability in its effectiveness, precooling poses a possible solution to lower
core temperature prior to exercise and may also have other yet to be determined benefits.
Fluid Replacement
One of the proposed treatments for an exertional heat illness is to rehydrate. It is
known that dehydration can exacerbate the effects of an exertional heat illness (Casa et
al., 2015), making rehydration a critical component in the prevention of heat illness.
There are two studies that looked at rehydration, one that had an ad-libitum policy for a
simulated army ruck march (Hailes et al., 2016); while the other simulated a military red
flag condition (wet-bulb globe temperature of 31.5-33.2°C) and had them consume
either water or ice-slurry every 10 minutes (2g/kg of bodyweight) (Nolte et al., 2010).
Hailes’ (2016) team had 12 participants walk for up to 3 hours in military red flag
conditions on a treadmill, and every 10 minutes the participants were hydrated with either
18

2g/kg bodyweight of either ice slurry or water (Hailes et al., 2016). The speed and grade
were set to 40% of the individuals VO2 peak from preliminary testing, the speed and
grade was lowered if the participant had trouble completing the testing procedures. The
slurry was 0°C and the water was above ambient temperature, roughly 35.5°C (Hailes et
al., 2016). Hailes team found no difference in core temperature and heart rate between the
water and ice slurry protocol (Hailes et al., 2016). It was discussed that this could
possibly be due to the gear that is involved as there is little to no breathability in military
gear thereby confounding cooling (Hailes et al., 2016).
Nolte et al. (2010) had 15 (13 male and 2 female) South African National Defense
Force soldiers conduct a 16.4km march outdoors on a track, during which the participants
were instructed to drink ad-libitum. Dependent variables were core temperature, total
body water, serum sodium concentration and plasma osmolality (Nolte et al., 2010). The
mean hourly ad-libitum water intake was 383mL, and average total body weight was
roughly 1kg (Nolte et al., 2010). Despite the changes in weight, there were no differences
seen in total body water, serum sodium concentrations and plasma osmolality (Nolte et
al., 2010). There was also no relationship observed between percent body mass lost and
core temperature values at the end of testing (Nolte et al., 2010). Core temperature was
maintained throughout the duration of this test (Nolte et al., 2010).
Balancing Protection and Health
One of the major issues that concerns military members is that it is a physically
taxing job to execute while wearing full gear and a combat uniform. The gear that is
being carried can differ in weight depending on what division a military member is in,
19

however, the infantry and gun-men crews usually carry an extra 33-45 kg of gear (Hunt et
al., 2016). Two different researchers both had study designs that examined the
physiological stress that load can cause during an extended march (Hunt et al., 2016;
Taylor et al., 2016).
One group of researchers had 37 Royal Australian infantry soldiers march for up
to 10km at a pace of 5.5km per hour on a flat outdoor surface (Hunt et al., 2016). The test
was conducted outdoors, and participants were given ques about pace at every 2.5km
mark (Hunt et al., 2016). The average temperature over the course of the testing was
23.1±1.8°C (Hunt et al., 2016). The participants wore full combat military gear and
equipment that weighed 41.9 ±3.6kg (Hunt et al., 2016). Core temperature and heart rate
were monitored continuously, and there was a heat illness symptomatic survey that the
participants completed after the march (Hunt et al., 2016). If anyone exhibited signs of an
exertional heat illness or had a core temperature greater than 39°C, they were removed
from the experiment (Hunt et al., 2016). Only 23 participants completed the race, 9
participants were removed due to exertional heat illness symptomology, and 5 due to
having a core temperature greater than 39°C (Hunt et al., 2016). What Hunt and his team
of researchers concluded was that the equipment that is being used might be preventing
some soldiers from completing their assignments. 14 out of the 37 infantrymen were
unable to complete the task at hand, representing ~38% of the group (Hunt et al., 2016).
If this were an actual mission, the group would not be able to function as well as it could
have if every member was healthy. Having the right equipment for any scenario is
important, but if a culmination of physical activity and too much external load inhibits a
20

military member from completing his or her mission; there is reason to either eliminate
some external load or to devise a physiological solution to aid in maintaining
homeostasis.
A team of researchers looked at the physiological strain that is caused by the
ballistic gear that military members wear (Taylor et al., 2016). They investigated these
effects in both a jungle terrain and then four separate trials in an urban environment as
well (Taylor et al., 2016). One trial was unloaded, and the other was loaded walking at
4km per hour for a duration of 90 minutes (Taylor et al., 2016). The 3rd and 4th trials were
also loaded and unloaded respectively, but this time the participants walked at 6km per
hour for up to 30 minutes or volitional fatigue (Taylor et al., 2016). What Taylor and his
team of researchers found was that throughout all experimental trials, work tolerance was
reduced as ballistic protection increased (Taylor et al., 2016). Taylor proposed that there
can be a balance between the appropriate amount of gear and the intensity at which the
soldiers are working, but the calculation of this balance has yet to be elucidated.

21

CHAPTER 3: METHODOLOGY
Participants
Approval for the current study was obtained from the Institutional Review Board
of East Stroudsburg University (Appendix A). Participant participation was voluntary,
and each participant underwent an orientation session where written informed consent
(Appendix B) was completed. Participants were recruited from graduate level exercise
science courses at a University in Northeastern Pennsylvania. This study was limited to
male participants due to potential confounding effects of the menstrual cycle associated
variations in core temperature and thermoregulation in females (Nagashima, K, 2015).
Participant Characteristics
The values (mean and SD ±) in Table 2 represent the participants (n = 6)
characteristics for demographic data (height, weight & age) as well as their activity
status. All six participants were recreationally active males. Initially 10 participants were
recruited, however, three dropped out before attending any testing sessions; and 1
participant dropped out after attending the first session due to an inability to commit to
participation in the entire study.
22

Table 1. Subject characteristics

Height
Weight
Age
Subjects (cm)
(kg)
(years)
1
178
87.2
24
2
188
83.3
25
3
185
103.7
22
4
183
97.7
23
5
170
77
23
6
196
97.3
24
Mean
183.3
91
23.5
SD (±)
8.1
9.3
1
Values were rounded to 1 significant figure.

Recreation
Status
Active
Active
Active
Active
Active
Active

Inclusion and Pre-Participation Requirements
To participate in this study, the participants were required to adhere to the
following set of guidelines. The participants were free from any previous heat illness and
any injury in the past year. The participants completed a Par Q, the principal investigator
added in the following question to the Par Q. “Have you ever suffered a heat
illness/injury? If yes, please list below” (Appendix C). A list of injuries that would
exclude participants can be found below (Table 2). Participants were recreationally active
at least three times per week following ACSM guidelines, 20-60 minutes of activity 3-5
times per week (Garber et al., 2011). Prior to experimentation, participants gave their
written informed consent and became familiarized with the protocol which is further
described below.

23

Table 2. List of lower extemity injuries that would exclude subject participation
List and descirption of injuries
Any broken bone in the lower extemity (foot, ankle, knee, femur)
Any sprained ligaments in the lower extremity
Any strained muscles or tendons in the lower extremity
If the participant had surgery on the lower extremity in the past year
Shin Splints
Any injury/surgery that occurred around the lower portion of the back/spine

Hydration Status
Before each session began, hydration status was assessed using urine
refractometry (Atago Hand-held Refractometer, Japan). The participants could proceed
with the protocol if they had a specific urine gravity of 1.020 or below which is indicative
of euhydration (How to Maximize Performance Hydration, NCAA., 2013). If the
participants were dehydrated, they were hydrated on site and a re-test of urine
refractometry was done to ensure hydration status. A description of rehydration can be
found below. Urine specific gravity was also assessed post-test, and if the scores were
reflective of dehydration, participants would ingest fluid and remain in the laboratory
until they were euhydrated as indicated by urine refractometry.
Hydration and Pre-conditions
Participant hydration status was monitored pre and post data collection through
urine refractometry. For this study design, any value 1.020 or below was considered
euhydrated, and anything above was considered dehydrated. If the test results were
indicative of dehydration, then the researchers gave the participant 16 ounces of water to
drink within 30 minutes. A second urine refractometry test was then administered after an
24

additional 30 minutes (How to Maximize Performance Hydration, NCAA, 2013). To
ensure hydration, participants were told to drink 16 ounces 2-3 hours before the session,
and they were advised to drink another 8 ounces of water 15 minutes before the session
(How to Maximize Performance Hydration, NCAA., 2013). Participants were asked to
refrain from heavy exercise (any type of cardio-endurance, interval training or lowerbody resistance training), alcohol, caffeine and any sort of stimulants one day prior to
testing. Two days before a testing session, the principal investigator would contact the
participant to remind them of their session time and date, as well as to remind them about
abstaining from heavy lower body resistance training the day prior.
Precooling Protocol
There was a 30-minute window to ingest 7.5 g/kg body mass (-1 ˚C or 0 ˚C) of ice
slurry or water (1 ˚C) before the exercise commenced (Siegel et al., 2010). At every 5minute window the participant ingested 1.25g/kg of bodyweight. Shortly after finishing
the precooling protocol the exercise commenced. The ice-slurry flavor the participants
consumed was blue raspberry (Snappy Popcorn Co, Breda, IA). One serving was 8oz and
contained 5 calories, 1mg of sodium 1g of carbohydrates and 1g of sugar.

25

Experimental Conditions
The participants were asked to complete three total sessions. Session 1 which was
familiarization, and sessions two and three which were either the experimental or control
trial. The order of sessions was randomized and counterbalanced for each participant
before the trials began. In every trial, the recreationally active individuals wore military
grade equipment.
Experimental Design
Visit one consisted of informed consent, measuring demographic data,
orientation, and familiarization. The participants completed and signed an informed
consent (Appendix B) prior to any testing sessions. The participants were oriented with
the study procedures and equipment prior to any testing, following which the participants
height and body mass were measured using a Detecto Stadiometer (Detecto, Webb City,
Missouri). Participants then underwent a familiarization trial which was designed to
orient the participants with the gear and equipment that were going to be utilized during
testing sessions. Full gear consisted of a combat uniform either ACU or OCP, summer
weight boots, a fighting load carrier vest (FLC), a ruck sack (15.8 kg) and a US Army
combat helmet.
Participants practiced walking on a treadmill at 4 mph and 0% grade for 15
minutes in order to become familiarized with the experimental protocol. If the pace was
too difficult, it was lowered until it could be kept at a challenging yet comfortable speed
(Nye et al., 2017). The exercise protocol originally was set to 4 mph and 0% grade, but it
26

proved to be too difficult for the participants in this study design. The exercise protocol
was then changed to a self-selected pace where the treadmill was set to 3.5 mph and 0%
grade. From there, the participants were instructed that they could increase or decrease
the speed from 0.1-0.5 mph in either direction. The screen was covered meaning the
participants were blinded to the speed. The investigator instructed the participants to
select a speed that was comfortable enough to sustain for a long period but would also be
challenging towards the end. Once the participant selected the speed, they felt was best,
the investigator recorded on the data sheet and started the timer to signal the start of the
test. The same speed was used during the participants next session still while being
blinded. All sessions occurred inside of a 10x10 Eurmax canopy tent (Eurmax 10x10
Canopy Tent, El Monte, California) at 33˚C, with full combat gear on and full lab
equipment on. The tent was heated to 33˚C using four space heaters (TPI 188 Portable
Heater, Gray, Tennessee), which took approximately 45 minutes to heat up to the correct
temperature. Visit two and three began with assessing hydration levels via the handheld
urine refractometer (Atago Hand-held Refractometer, Japan). If the participants were
euhydrated, they equipped the polar heart rate monitor, watch (Polar FT1, Beijing, China)
and the rectal thermistor (Measurement Specialties Model 701, Andover, Minnesota).
Once the equipment was put on, all resting variables were recorded which included heart
rate, core temperature, blood pressure and rating of perceived exertion (RPE).
Afterwards, the participants put on the full Army combat gear.
The precooling protocol was then initiated, which was to consume 7.5g/kg of
bodyweight in either ice slurry or water over a 30-minute period (Siegel et al., 2010).
27

Every 5 minutes, the participant consumed 1.25g/kg of bodyweight of either cold water
or ice slurry and this continued until 30 minutes had elapsed. Once the precooling
protocol was complete, the participants entered the heat tent and began the actual
experimental protocol which had a maximum test length of 90 minutes or until volitional
fatigue (Nye et al., 2017). The speed was a self-selected pace that ranged from 3.0 - 4.0
mph and 0 % grade (Nye et al., 2017) in a heat tent at 33±2˚C (Zimmerman et al., 2015).
The treadmill was set to 3.5 mph and the participant, not able to see the speed, was
instructed to increase or decrease the speed until they found a pace that was challenging.
Once the participant selected a speed the principal investigator recorded the pace on top
of the data sheet, as well as started the timer to indicate the start of the data collection
process. The same speed that the participant selected was replicated in the second
experimental trial. All variables were collected in 5-minute intervals which included,
heart rate (Polar H10, Beijing, China), core temperature (Measurement Specialties,
Andover, Minnesota; Cole-Parmer Instrument Co, Vernon Hills, Illinois) and RPE (RPE,
Borg, 1998) (Walker et al., 2015).
Heart rate, core temperature and RPE were collected every 5 minutes in both the
familiarization session as well as session two and session three (Walker et al., 2015). The
data collected during familiarization was not used and was discarded. Blood pressure was
collected pre and post testing via a stethoscope and sphygmomanometer. Heart rate was
collected through a polar heart band and polar heart rate watch. Core temperature was
collected via a rectal thermistor and was read through a tele-thermometer. RPE was
collected on a 6-20 Borg scale. Physiological strain index (PSI) was calculated after the
28

test using the data collected every 5 minutes. PSI is the indication of heat stress by
considering both metabolic (heart rate) and thermal (temperature) strain. The equation for
PSI is as follows: PSI = 5(Tret - Tre0). (39.5 - Tre0)-1 + 5(HRt - HR0). (180 - HR0)-1,
where Tret and HRt are any measures at a given interval and Tret0 and HR0 are the given
resting measurements (Cheung, S. S., 2010; Moran et al., 1998). The time points used in
calculating PSI for this study design were post dose consumption and recovery.
Heart rate and core temperature were monitored continuously for safety purposes.
The exercise trial was terminated either at participant request or if the participant met
termination criteria, listed below. The participant was immediately removed from the
heat tent and instructed to remove the US Army helmet, rucksack, jacket, boots, FLC and
pants. The participants then sat quietly for 5 minutes at which point post-exercise
measures were obtained. After the test was terminated, participants were removed from
the heat tent to return to normal resting heart rate and core temperature. A re-test of urine
refractometry was conducted, and if the participants were dehydrated, the researchers
administered fluids using the same hydration protocol found above until euhydration was
achieved.
Absolute Test Termination Criteria
1) Core temperature greater than or equal to 39.5 ˚C, (2) HR greater than 10 bpm
over age predicted maximum heart rate, (3) Unsteady gait making it unsafe to
continue walking, or (4) participant request (Hailes et al., 2016)

29

Keeping the participants safe was of the highest priority and if any of the
participants reached any one of the above criteria cut off points, the test would be
terminated. If the participant was unable to walk steadily on the treadmill with the extra
load carriage, the participants would be at risk of a fall. After one warning of an unsteady
gait, with a second occurrence resulting in test termination. Age predicted maximum
heart rate was calculated by the following: 220 – Age (Physical Activity Basics – CDC,
2018). No participant throughout the duration of the study design had a test terminated
due to one of the criteria above.
Statistical Analysis
Statistical analysis was performed using SSPS Version 24 for Windows (SSPS.,
Chicago, IL). The means and standard deviations were calculated for all variables that
were recorded during testing. T-tests was used to test the main effect of precooling on
time to volitional fatigue for each protocol. A series of one-way repeated measure
analysis of variance (ANOVA) were used to test the statistical significance of the
precooling protocol on core temperature and heart rate for both conditions. A Tukey post
hoc analysis was conducted to determine which precooling condition differed from each
other. Statistical significance was accepted with a p-value of p < 0.05. The smallest
worthwhile change was also calculated for the main effects of time to exhaustion and
core temperature using the explanation as done by Hopkins (Hopkins, W. G, 2016).

30

CHAPTER 4: RESULTS

Kinetic Results
The average time to exhaustion for the control condition was 26.33±8.22 minutes.
The average time to exhaustion for the experimental condition was 28.23±11.03 minutes.
The results of the paired sample t-test on time to exhaustion between conditions
demonstrated no significant difference (p = 0.227; t = -1.37). Figure 3 displays the mean
values for time to exhaustion per individual participant, across the two separate
conditions.

31

Figure 1. Mean time to exhaustion per participant by condition
*Indicates significance (p < 0.05) compared to the control condition

Table 3. Mean (SD) values for both conditions of all subjects per variable
Cooling Type
Control

Experimental

Core Temp
HR
RPE
TTE
Core Temp
HR
RPE
TTE
(˚C)
(BPM)
(minutes)
(˚C)
(BPM)
(minutes)
Mean 37.4
133.6
12.4
26.3
37.4
135.7
12.2
28.2
SD (±) 0.4
13.4
0.8
8.2
0.4
16.2
0.8
11
*Significant difference from control condition (p < 0.05); TTE = time to exhaustion (minutes); HR = heart rate (beats per
minute); RPE = rating of perceived exertion (on Borg's 6-20 scale). Figures were rounded to 1 significant figure.

32

Metabolic and Physiological Results
There was no statistical significant difference for core temperature (p = 0.876; f =
0.20) between the two conditions. The mean core temperature for control sessions was
37.36± 0.39˚C. The mean core temperature for the experimental group was 37.42± 0.39
˚C.
There was no statistical significant difference for heart rate (p = 0.763; f = 0.001)
between the two conditions. The control had a mean heart rate of 133.59±13.36 BPM
across all sessions and time intervals. For the experimental trials, the mean heart rate was
135.71±16.2 BPM. Figure 3 demonstrates the differences seen in heart rate between the
two conditions. The average temperature and humidity respectively in the control
sessions was 32.6 ˚C. and 29% relative humidity. For the experimental session, the
average temperature and humidity respectively was 32.5 ˚C. and 30% relative humidity.
The temperature of the environment and humidity for each participant respectively was
not significantly different (p = 0.741; p = 0.597).
Physiological strain index (PSI) was calculated and was then compared by
condition using a paired sample t-test. There was no significant difference found between
the experimental and control conditions (p = 0.604; t = -4.09). Mean PSI for the control
was 2.92±1.85 Mean PSI for the experimental condition was 2.46±1.10. Only one
individual reaching a score greater than 4 for both session 2 and session 3. Every other
individual was below a score of 4 which is considered minimal strain.

33

All averages from the figures included the baseline core temperature
measurements, post-dose (post precooling consumption) measurements, all data from the
5-minute intervals, and the recovery measurements.

Figure 2. Mean core temperature per participant by condition

34

Figure 3. Mean heart rate per participant by condition

35

Figure 4. Physiological strain index for all participants for both conditions

Smallest Worthwhile Change
The smallest worthwhile change was calculated to see if there were any
meaningful differences, since there were no statistically significant differences. The
standard deviation from the control condition was taken and multiplied by 0.2 to get the
smallest worthwhile change. If the experimental trial differed by the smallest worthwhile
change calculated from the control (per specific variable), then it was considered a
smallest worthwhile change. The smallest worthwhile change for core temperature in the
control sessions was 0.078 ˚C. For time to exhaustion, the smallest worthwhile change in
the control trial would be a difference of 1.644 minutes.

36

To make things simpler, the smallest worthwhile change was only looked at for
baseline measures, post-dose measurements and the recovery measures in participants 1,
4 and 5. These participants were chosen because of the differences observed in certain
variables throughout the study design. Participant 1 had positive smallest worthwhile
changes for core temperature, but not for time to exhaustion.
Participant 4 exhibited positive smallest worthwhile changes in both core
temperature and time to exhaustion. Participant 5 demonstrated no positive smallest
worthwhile changes for values of core temperature. Participant 5 did however,
demonstrate a positive smallest worthwhile change in time to exhaustion.

Figure 5. Time to exhaustion for three participants in both trials

37

Figure 6. Core temperature values separated by condition at different time intervals
for Participant 1

Figure 7. Core temperature values separated by condition at different time intervals
for Participant 4

38

Figure 8. Core temperature values separated by condition at different time intervals
for Participant 5

39

CHAPTER 5: DISCUSSION & CONCLUSION

Precooling Protocol and Statistics
The current investigation found no significant difference (p > 0.05) between
conditions for time to exhaustion. A control water supplement and experimental ice
slurry supplementation had similar results and ice slurry ingestion was ineffective in
increasing time to exhaustion. Siegel et al., (2012), examined the effects of a pre-exercise
precooling ice slurry as well as CWI compared to a precooling control water in 8 male
endurance runners. Running time was significantly longer in CWI and ice slurry
compared to control, however, there was no statistical difference between CWI and ice
slurry for time to exhaustion. This demonstrates that an ice slurry can be effective in
increasing time to exhaustion in certain performance tasks, and can even be compared to
have the same effect to that of a CWI cooling method.

40

Marino, F. E. (2002), reviewed 12 articles concerning precooling and its effects
on exercise performance. Out of the 12 articles in review, 7 found precooling with either
cold air at 0°C, 5°C, or water immersion at 24°C had increased performance in terms of
time to exhaustion or duration (Marino, F. E. 2002). One issue that Marino (2002)
addresses is that precooling is difficult to evaluate because of the multiple types of
exercise protocols employed. He states that various exercise protocols have been used,
but that very few of those protocols are actual measures of exercise performances. He
suggests that precooling is more beneficial for endurance events from 30-40 minutes, and
that precooling with higher intensity events are less well understood (Marino, F. E.
2002). The possibility exists that although that the exercise protocol could be considered
light endurance work, the added equipment mixed with task inexperience may have
resulted in relatively higher intensity for the participants and possibly ameliorated the
effects of the precooling protocol. This is further supported by the fact that the average
times to exhaustion for each condition were less than the 30 minute minimum exercise
duration suggested by Marino as benefiting from the precooling protocol (Marino, F. E.,
2002).
The results from the current study demonstrated no significant (p > 0.05)
difference between the separate conditions of control versus experimental for core
temperature. The precooling ice slurry ingestion was found to be ineffective at lowering
core temperature pre-exercise, which is in contrast to the findings of Siegel et al. (2010),
who investigated the effects of precooling with a slurry on running performance in the
heat and found that the precooling protocol with an ice slurry was effective in decreasing
41

core temperature and in turn increasing heat storage capacity. Zimmerman et al., (2015),
demonstrated that a pre-exercise crushed ice ingestion effectively lowered core
temperature in women cycling in 33°C heat, although it did not improve performance
measures. One of the potential limiting factors that may have affected these outcomes is
the low subject pool. If there were more subjects participating in the current study design,
these findings may have been more similar to that of Siegel et al. (2010) & Zimmermann
et al. (2015). Another possible limiting factor is that the control condition may have been
too similar to that of the experimental condition. The temperature of the two different
beverages from each condition were only 4°C apart. It is possible that both conditions
had worked to precool the individuals, and therefore no major difference was found
between the conditions.
The current investigation found no significant difference on the secondary effects
of heart rate, PSI & RPE compared amongst the two separate conditions (p > 0.05). These
findings were in contrast to that of Cotter et al., (2001) regarding heart rate and PSI.
Heart rate and physiological strain were significantly lower amongst the cold air
precooling group and ice vest group compared to control (Cotter et al., 2001). The current
study design had similar findings for RPE relative to the results found by Zimmermann et
al. (2015). Zimmermann imitated half time sports such as field hockey and soccer by
having 9 female participants execute 18 four second sprints in a heated environment
(33°C) (Zimmermann et al., 2015). Although the crushed ice ingestion did work to
significantly lower core temperature, it did not improve performance nor RPE which
were similar to the findings of this current study design (Zimmermann et al., 2015).
42

From the precooling of the slurry, it was assumed that there would be a visible
difference in core temperature from the baseline reading (B), to the post-dose
measurement (PD; completion of precooling protocol). However, what was found was
that core temperature was significantly different between B and recovery (R) which is
expected after physical exertion in the heat. The core temperature was not significantly
lowered from B to PD as was expected, and the core temperature was significantly higher
from B to R which was expected. There was also a significant difference between PD and
R, and since the precooling protocol was ineffective for this study design; it makes sense
that if core temperature did not change from B to PD, that it would also see a significant
increase in core temperature after physical exertion in the heat. If the precooling protocol
was effective, it would be anticipated that core temperature would be significantly lower
from B to PD, and significantly higher from PD to R. Siegel et al., (2010) demonstrates
that change from B to PD, where the ice slurry was effective and lowered core
temperature by 0.66°C compared with cold water ingestion which only lowered it by
0.25°C (Siegel et al., 2010).
Physiological Strain Index
One interesting point was that participants 4 and 5 were the only participants who
exercised beyond 30 minutes, and while their PSI scores were reflective of being in
higher strain than the other participants, all participants were classified as having minimal
strain. Cheung (2010) describes minimal strain as any value under 7, with a value over 7
being considered severe strain. Some participants only had PSI scores as high as 3 and

43

were usually below a value of 2. This could mean that potentially the exercise protocol
did not cause enough strain or that the participants chose an unchallenging pace.
Core Temperature End Point
The current study design found no significant difference (p > 0.05) between core
temperature end points amongst the separate conditions. The mean core temperature end
point for the control protocol was 37.8°C and for the experimental protocol 37.9°C (p =
0.932). One of the potential theories behind this study design was that the precooling
protocol could increase heat storage capacity from PD to R. Siegel et al. (2010)
mentioned by lowering core temperature before exercise, rectal temperature could
increase over a longer period of time and end at a similar temperature Cheung, S. S., &
McLellan, T. M., (1998), & Gonzalez-Alonso et al., (1999) demonstrated this to be true.
Cheung, McLellan and Gonzalez-Alonso found very similar core temperature end points
for both highly fit individuals and moderately fit individuals, who completed various
exercise protocols and fatigued around similar core temperature measurements. One of
the thoughts behind the design of the current study was to apply this to military members,
by allowing for a greater heat storage capacity. Theoretically the military members
should be able to increase their time to exhaustion, while at the same time; potentially
reducing the risk for exertional heat illness, but this was found to be untrue.
Future Considerations
Another issue with overheating and military members in general is the equipment
being worn. Convective, conductive and evaporative means of heat loss offer various
44

avenues for heat to leave the body, but it seems that the gear being worn by military
members inhibits evaporative heat loss (Nagashima et al., 2015). While the relative
humidity can also limit heat loss via evaporation, the long sleeve and pant leg design do
not offer much bare skin exposure for the sweat to evaporate. This lack of evaporative
ability may have been part of the impetus for the design of the CCV. A suggestion for the
future might include a potential redesign with either the length of the garment or material
of the equipment.
Some things to consider for future works would to try and increase the dose of the
slurry and to increase the number of participants. The small sample size that was used in
this study had an impact on the results and broadening the sample size can help with this
problem in the future. Also, if the participants have no experience with load carriage and
military gear, it is also suggested to have multiple familiarization sessions. Additionally,
it may be beneficial to collect measurements of local fatigue if utilizing participants
inexperienced with marching. In this study design, there were multiple participants who
described that the local fatigue of the lower extremity was a limiting factor and much
higher than overall fatigue. Another consideration is the fact that the self-selected speed
protocol may have not strained the participants adequately. The participants may have
selected a speed that was too easy, therefore not putting enough strain on the system to
see any changes. In the future, it might be beneficial once again to have experienced
marchers who can keep up with higher paces with increased loads.

45

Implications
In the current study, no participants had prior experience with load carriage. In
theory, this could have interfered with their normal gait kinetics and potentially change
the true time to exhaustion. These results differ from other studies in that the precooling
protocol that was employed was not effective. It may still be possible to lower the
chances of having an exertional heat illness and improve endurance performance in
military members with a precooling ice slurry, however, it was not so during this study
design.

46

Conclusion
The aim of this study was to investigate the effects of a precooling protocol ice
slurry (0±-1°C) compared to a control cold water (4°C) on military foot marches in
regard to core body temperature and time to exhaustion while wearing full combat gear
and a loaded pack in males aged 18 to 35. The results of this study found no statistically
significant difference on the main effects of core temperature and time to exhaustion; nor
was a difference observed for heart rate, RPE or PSI.
Continued research is warranted on not just precooling but any type of cooling
that can potentially increase heat storage capacity to increase time to exhaustion, while at
the same time reducing the chances of having an exertional heat illness. More research is
needed concerning the effects of the precooling protocol with military gear and using
actual military members with experience marching compared to recreationally active
individuals.

47

REFERENCES
Borg, G. (1998). Borg's perceived exertion and pain scales. Human kinetics.
Carter III, R., Cheuvront, S. N., Williams, J. O., Kolka, M. A., Stephenson, L. A., Sawka,
M. N., & Amoroso, P. J. (2005). Epidemiology of Hospitalizations and Deaths
from Heat Illness in Soldiers. Medicine & Science in Sports & Exercise, 37(8),
1338–1344. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=SPHS-1014623&site=ehost-live
Casa, D. J., DeMartini, J. K., Bergeron, M. F., Csillan, D., Eichner, E. R., Lopez, R. M.,
… Yeargin, S. W. (2015). National Athletic Trainers’ Association Position
Statement: Exertional Heat Illnesses. Journal of Athletic Training (Allen
Press), 50(9), 986–1000. Retrieved from
http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=109952408&si
te=ehost-live
Charkoudian, N. (2010). Mechanisms and modifiers of reflex induced cutaneous
vasodilation and vasoconstriction in humans. Journal of applied
physiology, 109(4), 1221-1228.
Cheung, S. S. (2010). Advanced Environmental Exercise Physiology.
Champaign, Illinois. Human Kinetics.

48

Cheung, S. S., & McLellan, T. M. (1998). Heat acclimation, aerobic fitness, and
hydration effects on tolerance during uncompensable heat stress. Journal of
Applied Physiology, 1998 May;84(5):1731-9.
Chinevere, T. D., Cadarette, B. S., Goodman, D. A., Ely, B. R., Cheuvront, S. N., &
Sawka, M. N. (2008). Efficacy of body ventilation system for reducing strain in
warm and hot climates. European Journal of Applied Physiology, 103(3), 307–
314. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=31648291&site=ehost-live
Cotter, J. D., Sleivert, G. G., Roberts, W. S., & Febbraio, M. A. (2001). Effect of precooling, with and without thigh cooling, on strain and endurance exercise
performance in the heat. Comparative Biochemistry and Physiology Part A:
Molecular & Integrative Physiology, 128(4), 667-677.
Dorman, L. E., & Havenith, G. (2009). The effects of protective clothing on energy
consumption during different activities. European journal of applied
physiology, 105(3), 463-470.
Garber, E, C., Blissmer, B., Deschenes, R, M., Franklin, A, B., Lamonte, J, M., Lee, M,
I., Nieman, C, D., & Swain, P, D., (2011).American College of Sports Medicine
position stand. Quantity and quality of exercise for developing and maintaining
cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy

49

adults: guidance for prescribing exercise. Med Sci Sports Exerc. 2011
Jul;43(7):1334-59. doi: 10.1249/MSS.0b013e318213fefb.
González-Alonso, J., Teller, C., Andersen, S. L., Jensen, F. B., Hyldig, T., & Nielsen, B.
(1999). Influence of body temperature on the development of fatigue during
prolonged exercise in the heat. Journal of applied physiology, 86(3), 1032-1039.
Hadid, A., Yanovich, R., Erlich, T., Khomenok, G., Moran, D., & Moran, D. S. (2008).
Effect of a personal ambient ventilation system on physiological strain during
heat stress wearing a ballistic vest. European Journal of Applied
Physiology, 104(2), 311–319. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=33937324&site=ehost-live
Hailes, S, W., Cuddy, S, J., Cochrane, K., & Ruby, C, B., (2016). Thermoregulation
During Extended Exercise in the Heat: Comparisons of Fluid Volume and
Temperature. Wilderness Environ Med. 2016 Sep;27(3):386-92. doi:
10.1016/j.wem.2016.06.004.
Hayes, M., Castle, P. C., Ross, E. Z., & Maxwell, N. S. (2014). The Influence of Hot
Humid and Hot Dry Environments on Intermittent-Sprint Exercise
Performance. International Journal of Sports Physiology & Performance, 9(3),
387–396. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=95701846&site=ehost-live
50

Hopkins, W. G, (2016). A New View of Statistics, Sport Science. Retrieved from
https://sportscience.sportsci.org/resource/stats/index.html
How to Maximize Performance Hydration, NCAA. (2013). Retrieved from
https://www.ncaa.org/sites/default/files/Performance%20Hydration%20Fact%20S
heetpdf
Hunt, A, P., Billing, D, C., Patterson, M, J., & Caldwell, J, N., (2016). Heat strain during
military training activities: The dilemma of balancing force protection and
operational capability. Temperature: Multidisciplinary Biomedical Journal. AprJun 2016; 3(2)307
Infantryman (11B). (2019). Retrieved from https://www.goarmy.com/careers-andjobs/browse-career-and-job-categories/combat/infantryman-11b.html
Jones, R, P., Barton, C., Morrissey, D., Maffuli, N., & Hemmings, S. (2012). Pre-cooling
for endurance exercise performance in the heat: a systematic review. BMC Med.
2012 Dec 18;10:166. doi: 10.1186/1741-7015-10-166.
Marino, F. E. (2002). Methods, advantages, and limitations of body cooling for exercise
performance. British journal of sports medicine, 36(2), 89-94.
Moran, S, D., Shitzer, A., Pandolf, B, K., (1998). A physiological strain index to assess
heat stress. Am J Physiol. 1998 Jul;275(1 Pt 2):R129-34. Retrieved from
https://www.ncbi.nlm.nih.gov/pubmed/9688970

51

Murphy, D. F., Connolly, D. A. J., & Beynnon, B. D. (2003). Risk factors for lower
extremity injury: a review of the literature. British journal of sports
medicine, 37(1), 13-29.
Nagashima, K., (2015). Thermoregulation and Menstrual Cycle. Temperature:
Multidisciplinary Biomedical Journal Jul-Sep 2015; 2(3)320. Retrieved from
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4843915/
Nolte, H., Noakes, T. D., & Vuuren, B. V. (2010). Ad Libitum Fluid Replacement in
Military Personnel during a 4-h Route March. Medicine & Science in Sports &
Exercise, 42(9), 1675–1680. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=53575597&site=ehost-live
NYE, E. A., EBERMAN, L. E., GAMES, K. E., & CARRIKER, C. (2017). Comparison
of Whole-Body Cooling Techniques for Athletes and Military
Personnel. International Journal of Exercise Science, 10(2), 294–300. Retrieved
from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=121855883&site=ehost-live
Phinney, L. T., Gardner, J. W., Kark, J. A., & Wenger, C. B. (2001). Long-term followup after exertional heat illness during recruit training. / Suivi a long terme apres
des pathologies lies a la chaleur pendant l ’ entrainement des recrues. Medicine &
Science in Sports & Exercise, 33(9), 1443–1448. Retrieved from
52

http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=SPHS790846&site=ehost-live
Physical Activity Basics. (2018, November 12). Retrieved January 2, 2019, from
https://www.cdc.gov/physicalactivity/basics/index.htm?CDC_AA_refVal=https://
www.cdc.gov/physicalactivity/basics/measuring/heartrate.htm
Pryor, R. R., Casa, D. J., Yeargin, S. W., & Kerr, Z. Y. (2018). Sports Medicine Staff
Size Influences Exertional Heat Illness Policies in High School
Football. International Journal of Athletic Therapy & Training, 23(4), 172–177.
Retrieved from
http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=130519157&si
te=ehost-live
Pryor, R, R., Suyama, J., Guyette, F, X., Reis, S, E., & Hostler, D., (2014). The Effects of
Ice Slurry Ingestion before Exertion in Wildland Firefighting Gear. Journal of
Prehospital Emergency Care Volume 19, 2015 - Issue 2. Retrieved from
https://www.tandfonline.com/doi/abs/10.3109/10903127.2014.959221
Selkirk, G. A., & McLellan, T. M. (2001). Influence of aerobic fitness and body fatness
on tolerance to uncompensable heat stress. Journal of Applied Physiology, 91(5),
2055-2063.
Siegel, R., Maté, J., Brearley, M. B., Watson, G., Nosaka, K., & Laursen, P. B. (2010).
Ice Slurry Ingestion Increases Core Temperature Capacity and Running Time in
the Heat. Medicine & Science in Sports & Exercise, 42(4), 717–725. Retrieved
53

from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=49210319&site=ehost-live
Siegel, R., Maté, J., Watson, G., Nosaka, K., & Laursen, P. B. (2012). Pre-cooling with
ice slurry ingestion leads to similar run times to exhaustion in the heat as cold
water immersion. Journal of sports sciences, 30(2), 155-165.
Smith, S. (2019). How to Train for Ruck Marches. Retrieved from
https://www.military.com/military-fitness/army-workouts/training-for-ruckmarches
Stacey, M. J., Parsons, I. T., Woods, D. R., Taylor, P. N., Ross, D., & Brett, S. J. (2015).
Susceptibility to exertional heat illness and hospitalization risk in UK military
personnel. BMJ open sport & exercise medicine, 1(1), e000055.
Taylor, N. A. S., Burdon, C. A., van den Heuvel, A. M. J., Fogarty, A. L., Notley, S. R.,
Hunt, A. P., … Peoples, G. E. (2016). Balancing ballistic protection against
physiological strain: evidence from laboratory and field trials. Applied Physiology
Nutrition & Metabolism, 41(2), 117–124. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=112684877&site=ehost-live
Walker, A., Driller, M., Brearley, M., Argus, C., & Rattray, B. (2014). Cold-water
immersion and iced-slush ingestion are effective at cooling firefighters following
a simulated search and rescue task in a hot environment. Applied Physiology,
54

Nutrition & Metabolism, 39(10), 1159–1166. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=98715535&site=ehost-live
Zimmermann, M. R., & Landers, G. J. (2015). The effect of ice ingestion on female
athlet.es performing intermittent exercise in hot conditions. European Journal of
Sport Science, 15(5), 407–413. Retrieved from http://navigatoresu.passhe.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db
=s3h&AN=102715466&site=ehost-live

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APPENDICES
APPENDIX A: Institutional Review Board Approval

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APPENDIX B
Informed Consent for Scientific Study
Title of Investigation: Investigating the Effects of Precooling on
recreationally active individuals during a Loaded Carriage Foot
March in Heated Conditions
Principal Investigator
Christopher Esposito
Overview of the study
Load Carriage foot marches are an integral part of military training. However, over the
last 20 years, different forms of heat illnesses have been plaguing cadets which hinders
both health and performance. Military branches have employed countermeasures but
most of these are not used due to cost or have been demonstrated as ineffective in
lowering core temperature and therefore preventing heat illnesses. The task at hand was
to identify a cost-effective method which can lower core temperature in hot conditions in
order to lower the chance of heat illnesses for military members. The purpose of the
present investigation is to gauge whether or not this precooling slurry protocol increased
heat storage capacity and increases time to exhaustion.
Testing Sessions
There will be three total sessions during this study. The first session will occur in the
Human Performance Lab (HPL) and end in the Research Laboratory. During that session,
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you will learn about what is going to take place in the study. If you wish to participate,
you will get your height and weight recorded. A 15-minute familiarization trial will occur
immediately after.
The next two sessions are roughly the same except the drink you will intake beforehand
is different. In one session you will drink 7.5g/kg of ice slurry (either blue raspberry or
cherry), and the other protocol you will drink 7.5g/kg of water. After ingestion, you will
enter a 93 ˚F heat tent with full combat gear and a rucksack on and walk on a treadmill
for up to 90 minutes. The speed of the treadmill is 4mph and the grade is at 0%.
You will be undergoing physical activity inside of a heat tent with full combat gear on
and a rucksack, although be it slight, there are still some risks involved. Any individual
information obtained from this study will remain confidential. Non-identifiable data will
be used for scientific presentations. You may withdraw from the study at any time. If you
have any questions you may contact the principal investigator or Dr. Chad Witmer before
signing this consent form. If you have any additional questions during or after this study,
Dr. Witmer can be contacted at:
cwitmer@po-box.esu.edu

Tel: (570) 422 3362

YOU ARE MAKING A DECISION WHETHER OR NOT TO PARTICIPATE. YOUR
SIGNATURE INDICATES THAT OYU HAVE READ THE INFORMATION
PROVIDED AND YOU HAVE DECIDED TO PARTICPIATE IN THE STUDY.

58

I have read and understood the above explanation of the purpose and procedures for this
study and agree to participate. I also understand that I am free to withdraw my consent at
any time.

Print Name

Signature

Witness Signature

59

Date

APPENDIX C

Physical Activity Readiness Questionnaire (PAR-Q) and
You
Regular physical activity is fun and healthy, and increasingly more people are starting to
become more active every day. Being more active is very safe for most people. However, some
people should check with their doctor before they start becoming much more physically active.
If you are planning to become much more physically active than you are now, start by
answering the seven questions in the box below. If you are between the ages of 15 and 69, the
PAR-Q will tell you if you should check with your doctor before you start. If you are over 69
years of age, and you are not used to being very active, check with your doctor.
Common sense is your best guide when you answer these questions. Please read the
questions carefully and answer each one honestly:
YES

NO

□ □ 1.

Has your doctor ever said that you have a heart condition and that you should only do
physical activity recommended by a doctor?

□ □ 2.

Do you feel pain in your chest when you do physical activity?

□ □ 3.

In the past month, have you had chest pain when you were not doing physical activity?

□ □ 4.

Do you lose your balance because of dizziness or do you ever lose consciousness?

□ □ 5.

Do you have a bone or joint problem that could be made worse by a change in your physical
activity?

□ □ 6.

Is your doctor currently prescribing drugs (for example, water pills) for your blood pressure
or heart condition?

□ □ 7.

Do you know of any other reason why you should not do physical activity?

□ □ 8.

Have you ever suffered a heat illness/injury? If yes, please list below.

Talk to your doctor by phone or in person BEFORE you start becoming much more physically active

If

or BEFORE you have a fitness appraisal. Tell your doctor about the PAR-Q and
which questions you answered YES.

you

You may be able to do any activity you want – as long as you start slowly and build up
gradually. Or, you may need to restrict your activities to those which are safe for you. Talk

answered:
•

with your doctor about the kinds of activities you wish to participate in
and follow his/her advice.
Find out which community programs are safe and helpful for you.

NO to all questions

Delay becoming much more active:

• If you are not feeling well because of a temporary If you answered NO honestly to
all PAR-Q illness such as a cold or a fever – wait until you feel questions, you can be
reasonably sure that you can: better; or

60