THE EFFECTS OF ACCENTUATED ECCENTRIC LOADING SCHEMES ON
CONCENTRIC POWER OUTPUT DURING THE BACK SQUAT PERFORMED BY
RESISTANCE TRAINED MEN

By
James P. Lemardy, 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
Student’s Name: James P. Lemardy, B.S.
Title: The Effects Of Accentuated Eccentric Loading Schemes On Concentric Power
Output During The Back Squat Performed By Resistance Trained Men
Date of Graduation: August 9, 2019
Thesis Chair: Gavin Moir, Ph.D.
Thesis Member: Shala Davis, Ph.D.
Thesis Member: Matthew Miltenberger, Ph.D.
Abstract
Previous research has indicated that resistance training utilizing accentuated
eccentric loading patterns augments concentric outputs. Mechanical stretch coupled with
eccentric overload may potentiate the concentric phase of the back squat. Therefore, it is
important to understand the various mechanisms involved and their potential relation to
increased concentric back squat performance. Purpose: The aim of the study was to
examine the differences in power output in college aged resistance trained males
performing traditional and AEL back squats. Subjects: Eight male volunteers (N= 8)
agreed to participate in the present study (age: 23.8 ± 1.6 years, mass: 84.3 ± 11.7 kg,
height: 174 ± 9 cm). All subjects had previous experience in resistance training and were
free from musculoskeletal injuries for up to one year. The subjects were asked to
complete three experimental conditions during which kinetic data was collected. The
three conditions were: Traditional (80/80% 1RM), AEL1 (105/80% 1RM), AEL2
(110/80% 1RM). Two repetitions were performed for each condition. Average power
output was collected immediately following each repetition during the back squat.
Results: The results showed a significant difference (p = 0.002) between the conditions.
There was a significant (p = 0.009) decrease in average power output from the AEL2
condition compared to the traditional and AEL1 condition. Conclusion: Utilizing AEL
patterns did not have any advantage over traditional loading patterns in terms of
enhancing average power production. The eccentric overload prescribed in the AEL2
condition may have been too much for the current population noted by the decrease in
performance. Future research is warranted on finding the optimal eccentric load to
enhance concentric performance.

ACKNOWLEDGEMENTS
I would first and foremost like to extend my gratitude to my advisors Dr. Gavin
Moir, Dr. Shala Davis, and Dr. Matthew Miltenberger for their guidance and continual
support throughout the entire thesis process. Furthermore, I would like to acknowledge
the entire Exercise Science Department at East Stroudsburg University for their
dedication in the pursuit of knowledge, and for leaving me with a strong academic
foundation. Finally, I would like thank my family and friends for their loving support and
encouragement during these past few years of my academic career. Cheers!

TABLE OF CONTENTS
LIST OF TABLES

vii

LIST OF FIGURES

viii

Chapter 1-Introduction

1

Purpose

5

Null Hypotheses

5

Operational Definitions

5

Limitations

6

Delimitations

6

Summary

6

Chapter 2-Review of Literature

8

Eccentric training

8

Neural Adaptations

10

Storage and Utilization of Elastic Energy

12

Stretch Reflex

14

Alterations in Contractile Machinery

15

Enhancing SSC Capabilities

17

Chapter 3-Methods

20

Subjects

20

Procedures

20

Data Collection Sequence

21

Instrumentation

22

Statistical Analysis

23
v

Chapter 4-Results

24

Chapter 5-Discussion

26

Conclusion

34

Practical Applications

35

References

36

List of Appendices
Appendix A
Institutional Review Board Approval

41

Appendix B
Written Consent

42

vi

LIST OF TABLES
Table
1. Mean power output production under different loading conditions

vii

25

LIST OF FIGURES
Figure
1. Individual best average power outputs across conditions

viii

25

CHAPTER 1
INTRODUCTION
Incorporating resistance training as part of an individual’s overall fitness
program is a proactive measure in preventing numerous diseases and physical
ailments associated with aging, and it has been shown to sustain quality of life by
restoring functional capacity (Feigenbaum, 1999). Resistance training is particularly
important to the athletic population for increasing performance and preventing
injuries. Athletic populations use resistance training to improve muscular strength,
size, power, speed, endurance, balance, and coordination (Kraemer, 2000).
Enhancing these skill related components of fitness is necessary to carry out the
motor performance skills required for optimal athletic performance (William,
Nicholas, Duncan, 2002).
Skeletal muscle adaptations occur specifically to the mode and intensity of
exercise (Coffey and Hawley, 2007). The frequency of training is equally as
important in driving long-term adaptations. Skeletal muscle seems to be responsive
to a mechanical stretch along the sarcolemma and is considered the primary
mechanism for exercise-induced adaptations (Coffey and Hawley, 2007). Mechanical
stretch coupled with overload is shown to be the most effective method to induce
1

skeletal muscle adaptations by adding sarcomeres in parallel and in series
(Goldspink, 1999).
Improving athletic performance becomes more challenging as training
experience increases. Therefore, other methods such as accentuated eccentric
loading techniques have been used to further elicit neuromuscular adaptations
(Walker et. al, 2016). There are various mechanisms responsible for the
augmentation of concentric performance during accentuated eccentric loading
(AEL). Increases in concentric performance can be attributed to the enhancement of
the SSC by the eccentric overload (Doan et. al, 2002). The manipulation of eccentric
loads to enhance maximum concentric force production is said to be responsible
through various mechanisms involving increased neural stimulation, recovery of
stored elastic energy, mechanical alterations, and increased preload. (Ojasto and
Hakkinen, 2009). Ojasto and Hakkinen (2009) found that utilizing AEL techniques
generates larger concentric power outputs than traditional training methods while
performing the bench press exercise.
It has been demonstrated that approximately 120% of concentric muscle
actions are produced by eccentric muscle actions (Munger et. al, 2017). This may
then suggest that traditional styles of training under load the eccentric phase
limiting concentric performance. This type of training is most applicable to athletes
who perform various multi-joint exercises that involve large muscle groups with the
purpose of enhancing power output or RFD (Munger et. al, 2017.) Doan and
associates (2008) state that increased eccentric loading is beneficial to induce acute

2

increases in concentric strength. Acute increases may depend on the current level of
training the athlete possesses.
Multiple studies have been done utilizing accentuated eccentric methods
during multi-joint movements. AEL patterns involve an eccentric overload phase
followed by a lower loaded concentric phase of a repetition (Ojasto and Hakkinen,
2009). A study done by Ojasto and Hakkinen (2009) compared traditional loading
patterns to dynamic accentuated external resistance loading (DAER) techniques
performed on the bench press and examined the effects on acute neuromuscular,
maximal force, and power responses. The authors concluded based upon their
findings that there were no changes in the maximum strength group performing
DAER loads of 105, 110, 120% of 1RM for the eccentric phase. In fact, utilizing these
techniques revealed lower concentric force values in the (105/100%, 110/100%
and 120/100%) conditions compared to the control group (100/100%) (Ojasto and
Hakkinen, 2009). This may imply that utilizing DAER techniques with eccentric and
concentric loads of this magnitude may not be beneficial to improving maximum
concentric strength. It was concluded that the traditional explosive strength group
did produce higher concentric peak power values for each individual in the 77.3 ±
3.2/50% from the control condition (50/50%) (Ojasto and Hakkinen, 2009). This
may imply that optimal loading should be individualized when using DAER
techniques when aiming to increase concentric power production (Ojasto and
Hakkinen, 2009). Walker and associates (2016) looked at AEL compared to
traditional isoinertial loading using the leg press in already strength-trained men.

3

These researchers found that accentuated eccentric techniques led to greater
strength gains, work capacity, and muscle activation (Walker et al., 2016). However,
the increases in muscle activation can be underpinned by the muscle damaging
effects of eccentric training and diminished concentric EMG amplitudes as a result of
altered motor unit recruitment and synchronization (Walker et. al, 2016). Different
responses to eccentric and concentric outputs may occur during AEL loading and
AEL cluster sets (Wagle et. al, 2018). The use of adding rest periods between each
repetition when performing AEL patterns is thought to be more beneficial for
maximizing concentric power output and RFD by reducing fatigue. Therefore, higher
power outputs can be maintained throughout repetitions because of less metabolite
accumulation (Wagle et. al, 2018). Employing short rest periods between each
repetition for the subjects is likely to provide even more relevant data because of
the ability to setup for the next repetition with readiness, which may demonstrate
more accurate differences in average power output between AEL conditions.
Previous research has shown that overloading the eccentric component of the back
squat when performing clusters displayed negative effects on peak power and
concentric work (Wagle et. al, 2018). A possible explanation for these findings is the
programming of 3 sets of 5 repetitions being too much volume inducing fatigue.
Previous literature has studied the potentiating effects of AEL techniques on
concentric outputs but little attention has been given applying it to the back squat.
Furthermore, the research that has been done looking at AEL techniques used loads
and repetition schemes that didn’t produce any meaningful results in concentric

4

power outputs. Performing AEL back squats with heavier eccentric loading and less
volume could possibly provide more applicable data because of the increased
preload necessary for the musculature involved and alterations in volume to reduce
fatigue. The current study used eccentric loads of greater magnitude for the subjects
performing AEL back squats and performed only two repetitions of each condition
with 30 seconds interrepetition rest in theory of inducing acute concentric
potentiation while avoiding metabolic fatigue.
Purpose

The purpose of the study was to examine the differences in power output in resistance
trained males performing traditional and AEL back squats.

Null Hypothesis
(There will be no difference in concentric power output in individuals performing
accentuated eccentric loaded back squats with 105/80% 1RM compared to traditional
loading patterns with 80/80% 1 RM.)
(There will be no differences in concentric power output in individuals performing
accentuated eccentric loaded back squats with 110/80% 1RM compared to traditional
loading patterns.)
Operational Definitions
For the purpose of this present study the following operational definitions applied:
1.) Resistance trained males- The subjects have 6 months or more of resistance
training experience
5

2.) Traditional Loading- eccentric and concentric loads are equated to 80% 1 RM.
3.) Accentuated Eccentric Loading – The subjects perform ECC loads of 105 and
110% 1RM followed by CON loads of 80% 1RM.
4.) Kinetic responses- Average power output during the concentric phase using a
Linear Positions transducer
5.) Stretch-Shortening Cycle- the transition time between the eccentric and
concentric phase
6.) Series Elastic Component (SEC)- containing fiber-cross bridges, aponeurosis, and
tendon
Limitations
For the purpose of this present study the following limitations applied:
1.) Level of adherence to pre-test conditions due to not having the ability to monitor
subjects outside of the testing time.
2.) Load knowledge testing may not demonstrate true maximal effort.
3.) Biomechanical differences between the subjects may impact the results.
Delimitations
1) Male subjects who are resistance trained for 6 months or more
2) Free from any musculoskeletal injuries for 1 year or more
3) Students from East Stroudsburg University
Summary
Previous research has indicated that resistance training that utilizes AEL patterns
produces higher power outputs throughout the concentric portion of the exercise being
6

performed. Some of the past literature has examined alterations in power output in the
bench and leg press. Some of the findings concluded that utilizing AEL patterns
throughout both exercises increased maximal force production and peak power
outputs. Previous research has examined AEL patterns with emphasis on greater
eccentric loads compared to concentric loads, however much of the studies done used
concentric loads that were ineffective for increasing concentric power output limiting
the outcome of the data.

7

CHAPTER 2
LITERATURE REVIEW
The purpose of the study was to examine the differences in power output in
resistance trained males performing traditional and AEL back squats. The following
chapter will present a review of the literature for the following: eccentric training,
neural adaptations, storage and utilization of elastic energy, stretch reflex,
alterations in contractile machinery, and enhancing stretch-shortening capabilities.
Eccentric Training
The eccentric portion of a muscle contraction occurs when a muscle is forced
to lengthen as a result of being placed under a load. The structural damage that
occurs to muscle fibers when the loaded muscle is forcibly lengthened ultimately
leads to a disruption of the sarcomeres within the myofibrils (Proske and Morgan,
2001). The sarcomeres become disrupted in series as a result of being overstretched
and eventually with enough structural damage to the muscle membrane a new
optimal length for tension will develop (Proske and Morgan, 2001). It is postulated
that after eccentric exercise, the non-uniformity of the sarcomeres creates a fall in
active tension creating a shift in the muscles optimum length for active tension

8

(Proske and Morgan, 2001). Although, metabolic factors such as diminished
excitation-contraction coupling process could be a possible mechanism for a fall in
active tension (Proske and Morgan, 2001). It is stated that the primary mechanism
behind skeletal muscle adaptations to eccentric exercise is based on the addition of
sarcomeres to restore muscle fibers and what drives the damage to the muscle is
dependent on sarcomere length (Proske and Morgan, 2001). The properties of
eccentric training and its effects on skeletal muscle provide an effective way to
maximize force while serving as a protective mechanism for athletes against injury.
Previous research has proven that the amount of force produced by eccentric
muscle actions is 20-60% greater than concentric actions (Mike et. al, 2017). The
eccentric phase of a muscle contraction in considered more beneficial than the
concentric phase at inducing hypertrophy in type IIx skeletal muscle (Walker et al.,
2016). The eccentric phase has been shown to produce more damage to the muscle
fibers being trained. Studies have proven that more tension is generated when
muscle fibers are being lengthened than when being shortened and with less
metabolic cost (Lorenz and Ramen, 2011). Previous research has shown that
muscles being lengthened eccentrically require less muscle activation and less fiber
recruitment to produce a given force (Lorenz and Ramen, 2011). Therefore, during
an eccentric contraction less metabolic waste is produced as a result of diminished
ATP utilization compared to the concentric phase (Lorenz and Ramen, 2011).

9

Neural Adaptations
Strength training stresses the central nervous system and can elicit neural
adaptations throughout skeletal muscle. As a result, chronic training adaptations lead to
increased force production. When training at high intensities, the CNS regulates force
production either by recruiting more motor units or increasing motor unit firing
frequency (Hedayatpour and Falla, 2015; Bradenburg and Docherty, 2002). However,
force production capabilities are often limited by incomplete activation of motor unit
recruitment or firing frequency (Gabriel, Kamen, and Frost, 2006).
Overloading the eccentric phase of a muscle action may increase motor unit
firing frequency and improve concentric front squat performance (Munger et. al, 2017).
These researchers found that concentric peak velocity and peak power significantly
increased in the heaviest AEL condition. They suggest that eccentric overload may
provide the stimulus needed to increase the rate of motor unit discharge during the
concentric phase enabling an individual to produce a higher RFD. Gabriel and associates
(2006) state that increased motor unit firing may be responsible for rapid increases in
force production at the onset of strength training. Significant increases in voluntary
activation of the quadriceps’ was discovered when performing AEL for 10 weeks of
bilateral leg press and knee extension exercises measured by twitch interpolation
techniques performing maximal isometric contractions (Walker et al., 2016). Altered
calcium levels can also be responsible for increased voluntary activation, which was
not accounted for in the study (Walker et. al, 2016). Twitch interpolation techniques
add a stimulus to voluntary contracting muscle to observe for any increases in force
10

production as a result of activating muscles not previously involved (Gabriel, Kamen,
and Frost, 2006). These researchers suggest that no differences in cross-sectional area
or EMG amplitude with concomitant increases in strength provide evidence of neural
enhancement.
Specific tension significantly increased 22% in the elbow extensors of subjects
performing AEL techniques pre to post training (Brandenburg and Docherty, 2002).
These researchers suggest neural mechanisms can be responsible for the increases in
specific tension due to subject unfamiliarity with the extensor exercise chosen.
Specifically, reductions in the co-activation of the antagonist muscle enables the agonist
muscle to be activated more effectively leading to enhanced force production in the
intended direction of movement (Brandenburg and Docherty, 2002; Aagaard et al.,
2000). However, Brandenburg and Docherty (2002) found significant increases in
specific tension at week 9 indicating more time might be needed to elicit this type of
neural adaptation.
Maximal motor unit firing rates decreased after 8 weeks of strength training in
both trained and untrained legs demonstrated by significant decreases in hamstring co
activation with no concomitant change in quadriceps EMG activity (Carolan and
Cafarelli, 1992). These results are in conjunction with previous research indicating that
initially strength related gains can be attributable to increased motor neuron firing rates
but after a period of time reduced co activation of the antagonist might be more
responsible (Brandenburg and Docherty, 2002; Gabriel, Kamen, and Frost, 2006). The
pre-stretch may cause an increase in neural drive that occurs during the eccentric phase
11

of a movement creating a potentiating effect and enabling more motor units to be
recruited for the concentric phase (Comyns and Flanagan., 2008). The same level of preactivation has been demonstrated when performing a depth jump as the drop height
increases. However, ground contact times must be short as well in order to get the full
potentiating effect.
Storage and Utilization of Elastic Energy
Mechanical work is stored as potential energy in the series elastic component
(SEC) when the active MTU is stretched (Cormie, McGuigan, and Newton (2011). This
energy is said to be stored mainly in the tendon, which contains nonlinear elastic
properties (Kurokawa et. al, 2003). Potential energy stored during the pre stretch of a
SSC movement can then be reutilized in the form of mechanical energy throughout the
concentric phase and contribute to positive work. Ojasto and Hakkinen (2009) suggest
that increases in eccentric EMG activity with a concomitant increase in power
production when performing AEL bench press actions may be attributable to the elastic
component. Individuals with higher levels of training might be able to return more
stored elastic energy through the early concentric phase when using greater AEL. The
optimal use of elastic strain energy may be dependent on the concept of resonance
suggesting that the frequency of the SSC movement should match the frequency of the
MTU (Walshe, Wilson, and Ettema, 1998). Kurokawa and associates (2003)
demonstrated rapid shortening of the muscle tendon complex by 5.3% of its original
length during upward phase II from (-100 to 0 ms) before takeoff during a CMJ. These
researchers stated that the energy during Phase II at toe off was released at a higher
12

rate than it was absorbed. It is possible that at this moment in time the rate of extension
matched the frequency of the MTU.
Timing of the eccentric portion of a muscle contraction can also have further
implications on increased strength and power for athletic populations. A previous study
has shown that performing eccentric contractions of 2, 4, and 6 seconds in duration of
barbell smith machine squats at 80-85% 1RM showed increases in average power
production across all 3 groups from baseline to post test jump squat protocols (Mike et
al., 2017). However peak velocity in the 6-second group performing jump squats
decreased (Mike et al., 2017). Possible mechanisms underpinning the decrease in peak
velocity throughout the jump squats protocols have to do with the SSC. An explanation
for this occurrence is the ineffective timing between the eccentric and concentric phase
of the jump limiting the force generating capabilities of the musculotendinous unit
(Mike et al., 2017). The ability of the elastic component of the MTU to return the energy
absorbed may have been comprised and lost as heat in the group performing 6 second
eccentric contractions during the jump squat protocol (Mike et al., 2017). It takes time
during the eccentric phase for the agonist muscle to generate a reasonable amount of
force before the concentric phase begins (Cormie, McGuigan, and Newton., 2011).
However, too much time to develop force can cause power outputs to decrease. Mike
and associates (2017) proved that the optimal duration for carrying out an eccentric
contraction in the barbell smith squat was 2 seconds in regards to increasing vertical
jump height which may have to due with the principle of specificity. Specificity of
training should be similar in the movement pattern and duration of contraction of a
13

given task for optimal transfer of an adaptation. The groups that held their contractions
for 4 and 6 seconds did not demonstrate any significant differences in vertical jump
height (Mike et al., 2017). The 6-second group showed a significant decrease in peak
velocity after performing jump squat protocols with 45% 1RM. A possible explanation
for the decrease in peak velocity could be due to the duration of the eccentric phase not
being specific enough to the duration of eccentric phase involved when performing a
vertical jump.
The Stretch Reflex
Doan and associates (2002) state a possible explanation for increases in
concentric force after performing AEL bench press movements may be the activation of
the muscle spindle, signaling more motor units to be recruited or increasing their firing
rate. A potential mechanism that may augment power production in movements
involving the SSC is the activation of spinal reflexes (Cormie et. al, 2011). During an
eccentric contraction muscle spindles located in the intrafusal fibers of a muscle are
activated by deformation stimulating a-motorneurons. The a-motorneurons activate
agonist muscles leading to greater developments of concentric force and power
production (Cormie et. al, 2011). Previous research has found that eccentric overload
increases the magnitude and rate of eccentric force development, which is thought to
enhance concentric force development due to a greater stretch of the MTU and
activation of the muscle spindle (Wagle et. al, 2018). Muscle spindles respond to rapid
changes in the length of a muscle, serving as a protective mechanism to the
musculotendinous unit (Comyns and Flanagan., 2008). When an eccentric stretch is
14

rapid enough, the muscle spindle acts as a mechanoreceptor responding to the rapid
change in length by activating an opposite contraction of the agonist muscle (Comyns
and Flanagan., 2008).
Producing greater concentric power outputs utilizing this mechanism of the SSC
also affects the storage and return of elastic energy from the musculotendious unit.
However, one thing to consider is the timing between both the eccentric and concentric
phases of the movement when looking for a potentiating effect on concentric power
output. The activation of the stretch reflex is important in activities such as running or
hopping because of their rapid stretch and short transition times. Increased stiffness of
the MTU increases the sensitivity of the muscle spindle to activate the stretch reflex
(Nicol, Avela, and Komi, 2006). Transition times between an eccentric and concentric
contraction is an important factor to consider when training an athlete based on the
principle of specificity.
Alterations in contractile machinery
Some studies suggest mechanical alterations to the muscle-tendon complex may
occur during stretch-shortening cycles. Such alterations have to do with the optimal
stiffness of the SEC (Wilson, Wood, and Elliot., 1991). The muscles and tendons are what
comprise the SEC. Optimal fascicle length and compliance of the tendon for a given task
may aid in producing large power outputs (Kurokawa et al., 2003). Based on the forcelength relationship an optimal amount of force can be produced depending on the
length of the sarcomere. The more compliant the tendon the faster the shortening
velocity of the concentric contraction will be accomplished by elastic recoil (Kurokawa et
15

al., 2003). Some researchers have proposed that during certain activities involving the
SSC, these alterations of the contractile machinery occur simultaneously enhancing
muscular performance.
Walshe, Wilson, and Ettema (1998) found significant increases in mechanical
work performed over the first 300ms of a concentric isokinetic squat preceded by
isometric preload and a stretch shorten cycle. The researchers suggested that increased
work output demonstrated in both conditions may indicate that greater tendinous
extension took place coupled with lower shortening velocity of the contractile element
contributing to enhanced force production based on the force velocity relationship.
Sheppard and Young (2010) studied 14 males, highly experienced in bench throw
exercises and found significant increases in barbell displacement across 3 AEL bench
throw conditions compared to the equal loading condition. They noticed that peak
concentric acceleration increased as the eccentric overload increased. They theorized
that increases in concentric acceleration and barbell displacement were most likely due
to an increased muscle contractile state.
Greater velocity and peak power was demonstrated when 16 strength trained
volleyball athletes performed AEL countermovement jumps compared to body mass
loaded jumps (Sheppard et. al, 2008). Sheppard and associates (2008) found no
significant differences in eccentric movement velocity or countermovement depth
between the two groups. The researchers suggested that the significant increases in
concentric performance produced by the AEL group may be due to less myofibrillar
displacement contributing to greater force production while the mass experiences
16

greater initial acceleration during the concentric phase. However, they stated the
myogenic mechanism most responsible for their observations was the increased active
state of the cross bridges to accommodate the greater force demands during the
accentuated eccentric loading phase. More cross bridge attachments lead to greater
joint moments initially during the concentric phase of the movement (Sheppard et. al,
2008).
Another study claimed that SSC activities augment force production by which the
tendinous structure produces high shortening velocities while the fascicles are operating
almost isometrically at an optimal length to produce large forces (Kurokawa et al.,
2003). Researchers suggested that activities such as sprinting which depend on creating
large forces more rapidly rely on a stiffer musculotendious unit (Wilson, Murphy, and
Pryor., 1994). However, this may only hold true if the force produced through this
mechanism overcompensates for any losses in the elastic return of energy from the
more compliant MTU. Wilson and associates (1994) demonstrated a relationship
between a stiffer MTU, isometric, and concentric force production but none for
eccentric force production. Again this indicates that a stiffer or more compliant
musculotendinous system may only be beneficial depending on the type and duration of
the contraction.
Enhancing SSC capabilities
The SSC capabilities of an athlete can be enhanced through plyometric training.
One of the most common modalities to enhance the fast SSC and enhance concentric
power output is a depth jump. An athlete performs a depth jump by dropping from a
17

fixed height and immediately upon touchdown carries out a vertical jump as explosively
as possible (Comyns and Flanagan, 2008). The purpose of a depth jump is to transfer
from the eccentric component when landing to the concentric component leaving the
ground as quickly as possible (Comyns and Flanagan, 2008). The quicker the exchange
between each contraction the more explosive the athlete is considered. The purpose of
this training method is to enhance the fast SSC by trying to achieve shorter contact
times (Comyns and Flanagan, 2008). This is beneficial to an athlete required to attain
maximum velocity in their movement through larger generations of power output
(Comyns and Flanagan, 2008). Comyns and Flanagan (2008) have observed contact
times of 0.25 and shorter and deemed it the threshold for short contact times elicited
by the fast SSC. Common depth jumps performed range from 10-40cm and contact
times observed could be long or short in duration depending on the power production
capabilities of the athlete (Comyns and Flanagan, 2008).
Comyns and Flanagan (2008) hypothesized that there is a threshold to depth
jump heights set at 50cm and above that can inhibit the fast stretch shortening cycle
having a negative impact on the athlete’s performance. Drop heights that are too high
hinder the athlete’s capabilities to transition from the eccentric to the concentric phase
effectively and produce high power outputs. The mechanism said to be responsible for
the reduction in power output during the concentric phase of a depth jump is the Golgitendon organ (GTO), (Comyns and Flanagan., 2007). The GTO is located in the extrafusal
fibers of skeletal muscle serving as a protective mechanism in response to muscle
tension (Comyns and Flanagan., 2007). Drop heights of 50cm or more stated by Comyns
18

and Flanagan (2007) produce greater landing velocities and may place too much tension
on the muscle activating the GTO complex. The result is an inhibitory effect on the
agonist muscles while simultaneously activating the antagonist muscles causing a
reduction in concentric power output.

19

CHAPTER 3
METHODS
The purpose of the study was to examine the differences in power output in
resistance trained males performing traditional and AEL back squats. This chapter will
present the following: subjects, procedures, instruments and data analysis.
Subjects
The subject group consisted of 8 college-aged resistance-trained males. Their
mean age was 23.8 ± 1.6 years, body mass (84.3 ± 11.7 kg), and height (174 ± 9 cm). All
subjects had previous experience in resistance training. At the time of data collection all
subjects were free from musculoskeletal injuries injury for one year. Ethical approval
was granted after review of the East Stroudsburg University Institutional Review Board
for the Protection of Human Subjects. All subjects provided written consent after
receiving verbal and written instructions, as well as the risks and benefits of the study.
Procedures
Prior to data collection all subjects were taken through a familiarization process.
During this session anthropometric measurements were taken and each subject was

20

instructed on squat depth and how the weight releasers work when performing
an AEL back squat action.
Data Collection Sequence
After completing the familiarization period the subjects completed two testing
sessions. The first testing session was for 1-RM assessment in the back squat. The
second testing session contained a single trial of each of the 3 different loading
schemes. The loading schemes were counterbalanced for each subject such that each
loading scheme was performed in different order. Both sessions were conducted with a
minimum of 72 hours in between to prevent fatigue. All participants were instructed to
wear proper footwear for testing. Before each testing session each subject performed a
standardized 10-minute warm-up protocol. The subjects performed 5 minutes of high
knees, butt kicks, walking lunges, and toe touches followed by the NSCA 1 RM back
squat warm-up protocol. A 2:1 tempo was established during the eccentric and
concentric phase of the back squat prior to beginning each testing session. An internal
knee angle of 90 degrees was used to indicate parallel for each testing session. This was
achieved by using a plyometric box adjusted in height accordingly to each subject. Two
spotters were present on each side of the barbell during both testing sessions to ensure
the participants safety.
During the first session the subjects 1 RMs were assessed utilizing the standard
NSCA 1-RM back squat protocol. The protocol consisted of 4 dynamic warm up sets to
get the participants ready to complete their one repetition max (1 RM) testing.

21

Following the warm up the participants had up to five attempts to reach their 1 RM.
Subjects 1 RM’s were indicated by a barbell speed of 0.22 m/s.
During the second session the participants completed a single trial of each of the
3 different eccentric loads based on percentages of 1-RM. The eccentric loads were
broken up into groups A (80%), B (105%), and C (110%). The concentric loads were made
the same for each loading scheme at 80% 1 RM. Trial one was a traditional loading
pattern of ECC (80%), CON (80%) of 1 RM. The experimental session (AEL) was made up
of trial two and three using ECC loads of (105, 110%) and CON loads of (80%). Each
subject received a demonstration utilizing the weight releasers before testing. To ensure
the releasers were adjusted to the right height and working properly, each individual
was instructed to perform the squat action down to the plyometric box with 10kg plates
on each releaser before actual testing with heavier loads. Before each trial the subjects
were instructed not to sit on the box at the end of the eccentric portion of the lift.
Instead they were told to touch the box and go, being as explosive as possible
throughout the concentric phase. The subjects were instructed to complete two
repetitions for each condition. Thirty seconds from the first repetition was allotted to
each subject to allow the spotters to replace the weight releasers back on the bar
before immediately performing another repetition. The subjects were given 5 minutes
of rest between each condition to allow for full recovery.
Instrumentation
The GymAware linear position transducer was used to measure the average
power outputs of each subject during the concentric phase of the lift. In order to
22

calculate average power output, the GymAware application will be downloaded on an
Apple Ipad and synchronized with the transducer. This application provides settings to
adjust based on body mass, barbell mass, and exercise modality. Given the previous
variables the application calculated average power output during the concentric phase
of the back squat.
Statistical Analysis
All statistical analyses were performed using SPSS (version 24.0 for Windows).
The results were provided as mean ranks between related groups. Average power
outputs from two repetitions under each condition were assessed. A non-parametric
Friedman test (p≤0.05) was applied to the data for statistical significances between the
group means. Also, a post hoc test was run on the data to examine where the
differences occur using a Wilcoxon signed-rank test on the different combinations of
related groups. To avoid systematic error, a Bonferroni-adjusted significance level
(p≤0.017) was calculated and applied to the data to compensate for multiple
comparisons between the groups.

23

CHAPTER 4
RESULTS

The purpose of the study was to examine the differences in power output in
resistance trained males performing traditional and AEL back squats. The values in Table
1 show the data for mean power production under different loading conditions. The
results of the Friedman test performed on the mean power output data revealed
statistically significant differences in power output depending on which loading
condition was used during the back squat, χ2(2) = 12.250, p = 0.002. Post hoc analysis
with Wilcoxon signed-ranked tests was conducted with a Bonferroni correction applied,
resulting in a significance level set at (p≤0.017). There were no significant differences
between the loading conditions of 80/80% and 105/80% (Z = -.707, p = 0.480). However,
there was a statistically significant reduction in power output in the 110/80% condition
vs. the 80/80% condition (Z = -2.598, p = 0.009). Also, there was a statistically significant
reduction in power output in the 110/80% condition vs. the 105/80% condition (Z = 2.598, p = 0.009).

24

Table 1. Mean Power (W) for Traditional (80/80%) and AEL (105/80%, 110/80%) Trials
80/80%

1266±412

105/80%

1194±429

110/80%

1081±425

2500
2046
Power Output (W)

2000

1500

80/80
1562.5

1450

105/80

1408.5
1171.5
964

1000

1004
728

500

0
1

2

3

4
5
Subjects

6

Figure 1. Individual best average power output across conditions

25

7

8

CHAPTER 5
DISCUSSION
The purpose of the study was to examine the differences in power output in
males performing traditional and AEL back squats. Previous literature has demonstrated
significant increases in individual peak and mean power production from the control of
50/50% to the AEL condition of 77.3 ± 3.2/50% (Ojasto and Hakkinen, 2009). Eccentric
overload enhanced concentric power and velocity during the front squat (Munger et. al,
2017). These researchers had their subjects perform 3 different eccentric overload
conditions over the course of 3 days. For the purpose of this study no significant
increases in concentric power output was observed in the AEL conditions. This could be
due to fatigue as a result of having the subjects complete 3 loading schemes in one
testing session. Other research has demonstrated statistically greater concentric
outputs utilizing accentuated eccentric cluster sets compared to traditional loading
patterns not including peak power (Wagle et. al, 2018). For the purpose of this study
significant decreases in mean power output were demonstrated between loading
conditions. These statistical differences were present between (80/80%, 110/80%) and
(105/80%, 110/80%) conditions.
26

In the current study no assumptions can be made in regards to AEL being more
beneficial than traditional loading patterns for increasing concentric power output. This
may be due to a very small sample size being used. Walker and associates (2016) found
significant differences in maximum concentric force production with a sample size of 28
males. The study was also carried out over 10 weeks increasing the probability of any
significant findings in their data. It has also been shown that previously resistance
trained individuals performing high intensity AEL showed statistically significant
improvements in repetitions to failure against concentric loads of 75% 1-RM (Walker et.
al, 2016). This suggests that AEL might be a better approach to take then traditional
loading patterns when it comes to completing greater workloads while minimizing
fatigue. Concentric 1-RM significantly increased in a study looking at AEL in the bench
press (Doan et. al, 2002). These acute increases that were demonstrated may be a result
of altering the 1RM load and weight on the hooks proportionally through multiple
successful attempts that were given to the subjects. The loading schemes in the current
study remained the same during each attempt regardless of the subject being successful
with the lift.
Performing traditionally loaded cluster set back squats produced significantly
greater concentric rates of force development and average velocity compared to
accentuated eccentric loaded clusters (Wagle et. al, 2018). The researchers in this study
claimed that the eccentric load might not have been large enough in magnitude to
induce potentiation in the concentric phase of the AEL cluster condition. Similarly, the
same assumption can be made in the current study. Previous research has suggested
27

that prescribing optimal eccentric loads when performing AEL seems to be highly
individualized (Wagle et. al, 2018). However, eccentric overload was not individualized
in the current study. A main effect was shown where peak velocity and peak power
were greater using eccentric loads of 120% compared to 105% during AEL front squat
protocols (Munger et. al, 2017). These findings contradict the results of the current
study where eccentric loads of 110% significantly decreased concentric power output
compared to the eccentric loads in the traditional (80%) and AEL (105%) conditions.
However, the relatively small sample size and large variability between subjects in the
present study should be noted.
The AEL condition (110/80%) in the current study was detrimental to concentric
power production indicating this prescribed load may have been too much for this
population. However, the Trad (80/80%) and AEL (105/80%) conditions showed no
statistical difference in power output. It is possible that a prescribed load somewhere in
between both of the AEL conditions would have shown a significant difference from the
traditional loading condition. Peak displacement was greater under all AEL conditions vs.
the traditional condition for males performing bench throws (Sheppard and Young,
2010). No significant differences in peak displacement occurred between AEL
conditions. This indicates that although peak displacement was significantly greater for
AEL’s vs. the traditional condition, each individual performed best under different AEL
conditions. Sheppard and Young (2010) found that the strongest athletes performed
their best bench throws with eccentric loads of 74.0 ± 8.9 kg compared to the weakest
athletes (62.0 ± 4.5 kg). However, the current study demonstrated that most of the
28

subjects produced higher power outputs in the traditional vs. AEL conditions regardless
of being the strongest or weakest in the back squat. Although, when instructed to touch
the box and explode up some of the subjects lost their balance, coupled with a slow
ascent once the weight releasers came off. This may be due to bilateral strength deficits
or training history. It is also possible that the subjects did not have enough experience
with AEL techniques and a longer familiarization period might have been needed.
Munger and associates (2017) stated that the magnitude of the pre stretch may
have been responsible for enhanced concentric peak power and peak velocity.
Performing front squats with AEL of 120% 1RM while activating the stretch reflex was
proven to be effective in producing higher concentric outputs (Munger et. al, 2017).
Eccentric loads of this magnitude may have been responsible for the observed
differences in peak power by increasing the velocity of stretch. However, an eccentric
tempo was set at 3 seconds by a metronome controlling the rate of descent. Mike and
associates (2017) found significant differences in vertical jump height after 4-weeks of
subjects performing 2 second eccentrics with submaximal loads in the squat. These
findings imply that eccentric contractions shorter in duration may increase power
output. For the purpose of this study the subjects were told to descend on a 2 second
tempo and come up from the box as explosively as possible. This prescribed eccentric
duration was considered adequate given the magnitude of the eccentric loads. The
larger power outputs expressed during the traditional loading condition might have
been due to the subjects descending at higher rates than in the AEL conditions.

29

Sheppard and Young (2010) state that two components that enhance the pre
stretch during a stretch cycling activity are the magnitude and rate of stretch. However,
no differences in eccentric depth or eccentric velocity were present but significant
differences in barbell displacement were demonstrated (Sheppard and Young, 2010).
Eccentric velocity during the countermovement across conditions was not recorded in
the current study. Eccentric overload great enough in magnitude may recruit larger
motor units and increase motor unit firing rates improving concentric performance
(Munger et. al, 2017). Munger and associates (2017) found that concentric peak velocity
and peak power significantly increased from eccentric overload of 105 to 120% 1RM. In
the present study, concentric power output decreased for all subjects in the AEL
(110/80%) condition. In this case, co-activation of the antagonist might have overridden
any advantages elicited by the recruiting of larger motor units or increased rates of
firing. Enhanced concentric power outputs were demonstrated in the AEL (105/80%)
condition by some of the subjects in the current study. It is possible that 105% of 1RM
was the optimal eccentric overload for some of the subjects to recruit larger motor units
and have them stay activated during the concentric phase increasing the velocity of
contraction. This implies that eccentric overload may need to be individualized to
benefit from AEL.
The fact that myoelectric responses using EMG weren’t accounted for in this
study might limit any kind of assumptions that can be made about possible
contributions from reflexive mechanisms. Therefor, increases or decreases in muscle
activation patterns in each individual between conditions weren’t examined. Performing
30

jumps with a pre stretch may lead to higher jumps caused by the rapid stretch of the
intrafusal muscle fibers and excitatory response of the a-afferent (Walshe, Wilson, and
Ettema, 1998). The use of EMG detects differences in muscle activation patterns that
may be due to a-afferent activation. Walshe and associates (1998) reported no
significant differences in muscular activation across SSC, concentric only, or isometric
preloaded squat conditions. Type Ib afferent motor neurons from the golgi tendon
organ may be responsible for decreased motor unit firing rates during 120% of 3RM
eccentric overload contractions (Balshaw et. al, 2017). These findings suggest that
eccentric loads great enough in magnitude might activate the GTO effecting concentric
performance. It is possible that this mechanism was responsible for the significant
decreases in power output in the AEL (110/80%) condition as a result of autogenic
inhibition. The contribution of EMG data can further give a better understanding if an
individual is GTO dominant by what’s going on with antagonistic muscles at different
levels of eccentric loading. Inferences can also be made from this type of data on what
types of training athletes should adopt to improve mechanisms that will override the
GTO. The training history of the subjects in the current study was not known.
A previous study demonstrated that acquired forces in excess of 1000 N at the
onset of shortening recorded by force plate data during a SSC and isometric preload vs.
concentric only smith machine squat resulted in more work in the first 200 ms (Walshe,
Wilson, and Ettema, 1998). Other potential mechanisms for these observed outcomes
by Wilson and associates (1998) may be due to increased active state of the muscle,
storage and return of strain potential energy, and the interaction of the muscle-tendon
31

complex. However, these researchers ruled out the elastic recoil of the series elastic
component as a possible contributor to the increased work because of little difference
in mean transitional force between the SSC and isometric preload conditions. The
current study did not include the use of a force plate. Therefor, it can’t be determined
which one of these mechanisms is more responsible than the other.
It is stated that when a musculotendinous units natural frequency is in sync with
the activity being performed using the SSC it is in resonance (Walshe, Wilson, and
Ettema, 1998). These researchers claim that the increased work over time initially in the
SSC vs. isometric preload condition may have been because of the optimal timing of the
extension. The timing of the eccentric phase was not tightly controlled in the current
study. It is possible that some of the subjects did not descend at their elastics systems
preferred rate of stretch throughout the AEL conditions. This may be the reason for
significant decreases in power output demonstrated in the AEL (110/80%) condition.
Without force plate data in the current study to examine other kinematic characteristics
involved no further assumptions can be made as to why each of the subjects power
outputs increased or decreased across conditions.
Varying levels of musculotendinous stiffness between subjects might explain
differences in power output among trials in the current study. Wilson, Murphy, and
Pryor (1995) state that performing an eccentric contraction with a stiffer MTU is thought
to be disadvantageous due to the stretching of the contractile element past its optimal
length hindering its force production. If a muscle is stretched to far it reduces the
overlap between actin and myosin thereby limiting concentric force production.
32

Depending on the magnitude of contraction, increases in the length of the contractile
element of the stiffer MTU could be detrimental to force production (Wilson, Murphy,
and Pryor 1994). For the purpose of the current study all subjects performed the back
squat to a plyometric box indicating a 90-degree internal knee angle. However, the
results by Wilson and associates (1994) suggest that there may be optimal ranges of
motion to enhance rate of force development in relation to MTU stiffness. These
researchers had their subjects performing eccentric and concentric bench press actions
at 90-degrees. A statistically significant energy difference over 0.37s of a concentric
bench press action was demonstrated between subjects with a more compliant vs. stiff
MTU (Wilson, Wood, and Elliot, 1991).
In the current study it can be postulated that some of the subjects performed
better under the AEL (105/80%) condition as a result of a stiffer MTU achieved through
strength training. Also some of the subjects may have performed better descending to a
90-degree internal knee angle because of having a stiffer MTU and this being the
optimal ROM to enhance force production. The muscle spindle may have been more
sensitive to stretch in some of the subjects due to a stiffer MTU and shorter ROM. The
activation of more a-motor neurons in response to the stretch reflex may be the
mechanism responsible for some of the increases in power output observed in the
(105/80%) condition. Other individuals performed their best in the traditional loading
condition possibly indicating they have a more compliant MTU. Although subjects with a
more compliant MTU may need to perform AEL over a larger ROM to activate the
muscle spindle or to take advantage of a larger storage and recovery of stored elastic
33

energy. It has been demonstrated that subjects with a stiffer MTU generated a higher
rate of force development and overall force during isometric and concentric vs.
eccentric bench press actions (Wilson, Murphy, and Pryor, 1994).
It is worth mentioning that in this study each subject was instructed to descend
to the plyometric box, touch, and immediately explode up concentrically. Concurrent
with previous literature by Ojasto and Hakkinen (2009), reductions in power output
were observed in the AEL (110/80%) loading condition vs. both the AEL (105/80%) and
Trad (80/80%) conditions. This may indicate that this load intensity might have been too
high for the subjects in this study to perform optimally. Other populations could be
better adapted for loads of this magnitude depending on training history.
Conclusion
Previous literature has demonstrated differences in concentric outputs in AEL vs.
traditional techniques (Ojasto and Hakkinen, 2009). However, the current study
demonstrated no statistical significance between the AEL (105/80%) and traditional
(80/80%) conditions. A significant decrease in power output was found from the AEL
(110/80%) vs. the AEL (105/80%) and traditional (80/80%) conditions indicating that
eccentric loading of this magnitude might be too high for this population. Large
variability present between all the subjects suggests that prescribing a load for the
eccentric phase of the AEL conditions should be based on the individual and not as a
group.
Decreases in power output found as the load in the eccentric phase reached
110% of 1RM demonstrates the need for further analysis using EMG and force plate
34

data. Loads of this magnitude might be disadvantageous to the mechanisms that
augment power production. Changes in power production between the trials could be
attributed to the stiffness of the MTU.
In agreement with prior literature MTU stiffness is significantly related to
concentric performance (Wilson, Murphy, and Pryor, 1994). Reductions in power output
were noticed for each subject in the heaviest AEL condition. This suggests that subjects
may require a stiffer MTU to produce higher power outputs when performing AEL
techniques with supra maximal eccentric loads. Further analysis may be necessary
examining all the mechanisms responsible for enhanced concentric performance.
Practical Applications
In the current study, utilizing AEL over traditional loading techniques
demonstrated no usefulness for increasing concentric power production. The study
shows that the subjects may have not had the desired level of training to handle the
eccentric overload in the one AEL condition that lead to decreased performance. The
current data suggests that prescribing loads for the eccentric phase of AEL conditions
may need to be individualized to enhance concentric power production based on the
subject’s level of training and optimal stiffness. A longitudinal study may be necessary
for augmenting concentric power output elicited by AEL over traditional loading
techniques.

35

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41

Informed consent for scientific study

Title of investigation: The Effects of Accentuated Eccentric Loading
Schemes on Concentric Power Output during the Back Squat
Performed by Resistance Trained Men.

Principle investigator: James Lemardy

Overview of study
Accentuated eccentric loading has been used to generate increases in concentric power output
when performing a variety of resistance training exercises. Linear position transducers are often
used to calculate power output when performing a back squat. Despite the widespread use of this
testing equipment, there is a limited amount of information pertaining to the different methods
used to calculate power output. All testing will be performed on-campus at East Stroudsburg
University.

Testing sessions
There will be two testing sessions during the study. Both sessions will be performed in the
Undergraduate Laboratory of East Stroudsburg University. During the testing sessions you
will be asked to perform four AEL back squats and 2 traditional back squats. Prior to the
squats you will be taken through a standardized warm-up.

Although you will be undergoing physical testing, there is very little risk if you are a normal
healthy individual. Individual information obtained from this study will remain confidential.
Non-identifiable data will be used for scientific presentations and publications. You may
withdraw from the study at any time. If you have any questions please ask Dr Moir before
signing this consent form.

If you have any additional questions during or after the study, Dr Moir can be contacted at:

gmoir@po-box.esu.edu

Tel: (570) 422 3335

42