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Countermovement Jump Inter-Limb Asymmetries in Collegiate Basketball Players

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The purpose of the present study was to establish the intrasession and intersession reliability of variables obtained from a force plate that was used to quantitate lower extremity inter-limb asymmetry during the bilateral countermovement jump (CMJ). Secondarily, a comparison was performed to determine the influence of the jump protocol CMJ with or without an arm swing (CMJ AS and CMJ NAS, respectively) on inter-limb asymmetries. Twenty-two collegiate basketball players performed three CMJ AS and three CMJ NAS on dual force platforms during two separate testing sessions. A majority of variables met the acceptable criterion of intersession and intrasession relative reliability (ICC > 0.700), while fewer than half met standards established for absolute reliability (CV < 10%). CMJ protocol appeared to influence asymmetries; Concentric Impulse-100 ms, Eccentric Braking Rate of Force Development, Eccentric Deceleration, and Force at Zero velocity were significantly different between jumping conditions (CMJAS versus CMJ NAS; p < 0.05). The present data establish the reliability and smallest worthwhile change of inter-limb asymmetries during the CMJ, while also identifying the influence of CMJ protocol on inter-limb asymmetries, which can be useful to practitioners and clinicians in order to effectively monitor changes associated with performance, injury risk, and return-to-play strategies.
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sports
Article
Countermovement Jump Inter-Limb Asymmetries in
Collegiate Basketball Players
Aaron Heishman 1, 2, *, Bryce Daub 2, Ryan Miller 1, Brady Brown 1,2, Eduardo Freitas 1and
Michael Bemben 1
1Department of Health and Exercise Science, University of Oklahoma, Norman, OK 73019, USA;
ryanmiller1@ou.edu (R.M.); brownbrady3@ou.edu (B.B.); eduardofreitas@ou.edu (E.F.);
mgbemben@ou.edu (M.B.)
2Department of Athletics, Basketball Strength and Performance, University of Oklahoma,
Norman, OK 73019 USA; bdaub@ou.edu
*Correspondence: aaronheishman@ou.edu
Received: 27 February 2019; Accepted: 26 April 2019; Published: 30 April 2019

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Abstract:
The purpose of the present study was to establish the intrasession and intersession
reliability of variables obtained from a force plate that was used to quantitate lower extremity
inter-limb asymmetry during the bilateral countermovement jump (CMJ). Secondarily, a comparison
was performed to determine the influence of the jump protocol CMJ with or without an arm swing
(CMJ AS and CMJ NAS, respectively) on inter-limb asymmetries. Twenty-two collegiate basketball
players performed three CMJ AS and three CMJ NAS on dual force platforms during two separate
testing sessions. A majority of variables met the acceptable criterion of intersession and intrasession
relative reliability (ICC >0.700), while fewer than half met standards established for absolute
reliability (CV <10%). CMJ protocol appeared to influence asymmetries; Concentric Impulse-100 ms,
Eccentric Braking Rate of Force Development, Eccentric Deceleration, and Force at Zero velocity
were significantly dierent between jumping conditions (CMJAS versus CMJ NAS; p<0.05). The
present data establish the reliability and smallest worthwhile change of inter-limb asymmetries
during the CMJ, while also identifying the influence of CMJ protocol on inter-limb asymmetries,
which can be useful to practitioners and clinicians in order to eectively monitor changes associated
with performance, injury risk, and return-to-play strategies.
Keywords:
athlete monitoring; athlete performance; reliability; fatigue monitoring; bilateral
countermovement jump; CMJ arm swing; CMJ without arm swing
1. Introduction
Assessing and monitoring mechanical inter-limb dierences, or asymmetries, has become an
increasingly common practice among researchers, coaches, and clinicians in an eort to provide
insight into athletic performance, injury prevention, and rehabilitation. More specifically, increases in
lower-limb power asymmetries have been associated with decreases in jump height and sprint speed,
as well as reductions in change-of-direction speeds [
1
3
]. Similarly, asymmetries in movement patterns
have been proposed as a factor increasing injury risk [
4
6
]. Inter-limb asymmetry measurements have
also been found to be useful in quantitating functional deficits following an injury, and when guiding
an athlete’s readiness to return-to-play and later return-to-performance as part of the rehabilitation
process [
7
9
]. The continued advancement of viable field tests that are non-invasive and time-ecient
is essential in order for practitioners and clinicians to frequently monitor changes in inter-limb
asymmetries that may be detrimental to performance or place athletes at an elevated injury risk.
Sports 2019,7, 103; doi:10.3390/sports7050103 www.mdpi.com/journal/sports
Sports 2019,7, 103 2 of 15
A variety of methods have been used to assess lower-limb force and strength asymmetries
[10,11]
.
The isokinetic force test is the most common means of testing asymmetries; however, the
arthrokinematics and contraction speed of isokinetic testing vastly dier from those encountered
during sport [
12
]. Previous literature noted the inability of isokinetic assessments to identify bilateral
symmetries alone, with more sport-specific assessments required to reveal asymmetries [
13
]. Moreover,
isokinetic testing requires expensive equipment and lacks the time eciency required for frequent
assessments of numerous athletes in the team-sport setting. Limitations associated with isokinetic
testing have steered the development of more functional assessments to measure lower extremity
asymmetries, including the single-leg countermovement jump (SLCMJ), as well as the bilateral
countermovement jump (CMJ) [10,12,14].
In contrast to isokinetic testing, the SLCMJ and CMJ oers a functional assessment paralleling the
dynamic, closed-chain movement experienced in sport, while also incorporating the stretch-shortening
cycle (SSC) [
12
,
15
]. Although the SLCMJ does oer an advantage over isokinetic testing as a dynamic
functional assessment, it is not without limitations, as performance can be influenced by additional
factors, such as movement coordination and balance [
12
,
16
]. These factors have led to a closer
examination of the utility of the CMJ. The CMJ is commonly used in the applied performance setting
to monitor acute changes in neuromuscular readiness and fatigue, while also used to assess long-term
changes in performance qualities, such as adaptations to a training program [
17
20
]. Previously,
Impellizzeri et al. [
12
] developed an assessment to quantify asymmetries in peak vertical ground
reaction forces during the CMJ, where athletes jump with one foot placed on a force plate and the other
on a wooden platform to isolate the individual limb contributions during the jump. However, the CMJ
is increasingly being performed on dual force plates, with each lower limb positioned on an individual
force platform. The dual force platforms can be synchronized to provide the conventional analysis of
bilateral actions during the CMJ [
21
], while also simultaneously monitoring the force-time signature of
each individual limb, allowing the delineation of lower-limb force contributions and asymmetries.
The CMJ involves the dynamic muscle function known as the stretch-shortening cycle (SSC) [
15
].
Although the SSC requires both concentric and eccentric muscle actions, previous research investigating
lower-limb asymmetries has only focused on variables revolving around the concentric phase (i.e.,
force, power, etc.), neglecting the performance of the eccentric portion [
19
,
21
]. However, examining the
characteristics of the eccentric phase may oer novel insights associated with changes in neuromuscular
function and movement strategies during the CMJ [
22
]. Therefore, establishing the reliability of
lower-limb asymmetry throughout the entire CMJ force-time signature may be critical for performance
practitioners and clinicians to eectively monitor changes associated with performance, injury risk,
and return-to-play strategies.
Two methods are commonly employed when performing the CMJ. The first approach incorporates
the use of the arm swing (CMJ AS), and has been suggested to facilitate a higher level of sport-specificity,
as well as enhance performance during the CMJ [
21
,
23
,
24
]. However, it is speculated that the arm
swing may counteract lower extremity actions and mask lower limb force asymmetries. In contrast,
the second approach eliminates the influence of the arm swing by requiring the athletes to maintain
hand placement on the hips or fixed to a virtually weightless implement (e.g., a polyvinyl chloride
pipe or wooden dowel) positioned on their shoulders throughout the duration of the CMJ (CMJ
NAS) [
12
,
13
,
18
,
21
]. Proponents of this protocol suggest that the elimination of the arm swing isolates
lower extremity function and reduces the potential variability introduced by performing the arm swing
movement. However, the unfamiliar nature of eliminating the arm swing during the CMJ has been
speculated to modify movement strategies, especially in athletes participating in sports that involve
substantial amounts of jumping. In addition, it is speculated the arm swing may counteract lower
extremity action and mask lower limb force asymmetries. While the reliability of the CMJ has been
established when lower-extremity outputs are assessed in conjunction [
18
,
19
,
21
], to our knowledge, no
evidence exists that specifically identifies the influence of the CMJ AS and CMJ NAS on the reliability
of inter-limb asymmetries during the bilateral CMJ.
Sports 2019,7, 103 3 of 15
Previous literature has consistently considered an asymmetry greater than 10% between limbs as
clinically relevant, and this threshold has been used as a criterion to guide return-to-play following
injury [
7
,
8
,
11
]. However, the lack of data establishing the reliability and smallest worthwhile change
in inter-limb asymmetry may make the traditional 10% rule unqualified, as it would not allow the
separation of the “signal” from the “noise” [
25
]. While research has established the reliability of
the CMJ [
18
,
21
], the reliability and the smallest worthwhile change of lower extremity inter-limb
asymmetries during the CMJ remains to be explored. Further, although both CMJ protocols (CMJ AS
and CMJ NAS) have been used to evaluate lower extremity inter-limb asymmetries [
12
,
13
,
16
,
24
], to our
knowledge, previous research has yet to identify the influence of the CMJ protocol, with or without
the arm swing, on the reliability of lower extremity inter-limb asymmetries. Therefore, the primary
purpose of the present investigation was to establish the intersession and intrasession relative and
absolute reliability of variables obtained from a force plate used to quantitate lower extremity inter-limb
asymmetry during both the CMJ AS and CMJ NAS in a cohort of healthy collegiate basketball players.
A secondary purpose was to examine inter-limb symmetry between the CMJ AS compared to the CMJ
NAS. It was hypothesized that both CMJ protocols would meet acceptable standards of relative and
absolute reliability. Additionally, it was hypothesized that there would be dierences in asymmetries
between jump protocols, with CMJ AS demonstrating a reduction in between limb asymmetries.
2. Materials and Methods
2.1. Subjects
A convenience sample of 22 (Men: n =14, age =19.7
±
1.0 years, height =1.98
±
0.71 m, body
mass =94.7
±
6.2 kg; Women: n =8, age =20
±
1.6 years, height =1.80
±
0.65 m, body mass =78.2
±
8.3 kg) National Collegiate Athletic Association (NCAA) Division 1 collegiate basketball players were
included in this study. All the subjects were active squad members of the University of Oklahoma’s
Men’s and Women’s Basketball teams and were free of any acute musculoskeletal injuries at the time of
testing. This research was approved by the Institutional Review Board of the University of Oklahoma,
and all the subjects provided written, informed consent before participating in the study. In addition,
this study conforms to the standards set by the Declaration of Helsinki.
2.2. Design
A randomized cross-over within-subject study design was utilized to examine the reliability of the
side-to-side limb symmetry of CMJ variables during both the CMJ AS and the CMJ NAS. As illustrated
in Figure 1, during two dierent testing sessions, which were separated by at least one week, subjects
performed three CMJs with an arm swing and three CMJs with no arm swing, in a randomized order.
Sports 2019, 7, x FOR PEER REVIEW 3 of 16
Previous literature has consistently considered an asymmetry greater than 10% between limbs
as clinically relevant, and this threshold has been used as a criterion to guide return-to-play following
injury [7,8,11]. However, the lack of data establishing the reliability and smallest worthwhile change
in inter-limb asymmetry may make the traditional 10% rule unqualified, as it would not allow the
separation of the “signal” from the “noise” [25]. While research has established the reliability of the
CMJ [18,21], the reliability and the smallest worthwhile change of lower extremity inter-limb
asymmetries during the CMJ remains to be explored. Further, although both CMJ protocols (CMJ AS
and CMJ NAS) have been used to evaluate lower extremity inter-limb asymmetries [12,13,16,24], to
our knowledge, previous research has yet to identify the influence of the CMJ protocol, with or
without the arm swing, on the reliability of lower extremity inter-limb asymmetries. Therefore, the
primary purpose of the present investigation was to establish the intersession and intrasession
relative and absolute reliability of variables obtained from a force plate used to quantitate lower
extremity inter-limb asymmetry during both the CMJ AS and CMJ NAS in a cohort of healthy
collegiate basketball players. A secondary purpose was to examine inter-limb symmetry between the
CMJ AS compared to the CMJ NAS. It was hypothesized that both CMJ protocols would meet
acceptable standards of relative and absolute reliability. Additionally, it was hypothesized that there
would be differences in asymmetries between jump protocols, with CMJ AS demonstrating a
reduction in between limb asymmetries.
2. Materials and Methods
2.1. Subjects
A convenience sample of 22 (Men: n = 14, age = 19.7±1.0 years, height = 1.98 ± 0.71 m, body mass
= 94.7 ± 6.2 kg; Women: n = 8, age = 20 ± 1.6 years, height = 1.80 ± 0.65 m, body mass = 78.2 ± 8.3 kg)
National Collegiate Athletic Association (NCAA) Division 1 collegiate basketball players were
included in this study. All the subjects were active squad members of the University of Oklahoma’s
Men’s and Women’s Basketball teams and were free of any acute musculoskeletal injuries at the time
of testing. This research was approved by the Institutional Review Board of the University of
Oklahoma, and all the subjects provided written, informed consent before participating in the study.
In addition, this study conforms to the standards set by the Declaration of Helsinki.
2.2. Design
A randomized cross-over within-subject study design was utilized to examine the reliability of
the side-to-side limb symmetry of CMJ variables during both the CMJ AS and the CMJ NAS. As
illustrated in Figure 1, during two different testing sessions, which were separated by at least one
week, subjects performed three CMJs with an arm swing and three CMJs with no arm swing, in a
randomized order.
Figure 1. The study design and flow of testing. During Test Session 1, subjects performed either three
CMJ AS or three CMJ NAS in a randomized order, followed by three jumps of the other protocol.
During Test Session 2, subjects performed the same number of jumps in the reciprocal order. CMJ
represents countermovement jump; AS represents arm swing; NAS represents no arm swing.
Figure 1.
The study design and flow of testing. During Test Session 1, subjects performed either three
CMJ AS or three CMJ NAS in a randomized order, followed by three jumps of the other protocol.
During Test Session 2, subjects performed the same number of jumps in the reciprocal order. CMJ
represents countermovement jump; AS represents arm swing; NAS represents no arm swing.
Sports 2019,7, 103 4 of 15
2.3. Procedures
All the testing took place within a two-week time frame during the o-season training period.
Subjects performed two testing sessions, with both sessions including three CMJ AS and three CMJ
NAS. The order of jump type was randomly assigned during Test Session 1, and subjects performed
the jump type in the reciprocal order during Test Session 2. A minimum of two minutes of rest was
allotted between jump trials. In addition, each subject performed both testing sessions within the same
hour, and all the subjects performed their testing in the afternoon between 13:00 and 14:00, as previous
literature has identified the influence of time of day on jump performance [
26
]. In accordance with
prior literature [
18
,
21
] and in an attempt to control the impact of training loads on testing outcomes,
CMJ testing was performed within the same time frame of the training week, and training loads were
strictly matched 72 h prior to both testing sessions, with sport-specific practice duration matched in the
days prior to both testing sessions. Further, subjects were instructed to have no physical exertion or
exercise prior to arriving on days of testing. In an eort to maintain ecological validity, subjects wore
their standard practice gear, including shoes of their choosing, but each subject was required to wear
the same pair of shoes during both testing sessions. While no dietary restrictions were implemented,
athletes were instructed to maintain normal dietary intake, as outlined by the team’s sports nutritionist.
To limit the impact of instructions on the CMJ performance characteristics, consistent instructions were
provided to all the subjects during each CMJ trial. In addition, verbal encouragement was provided to
encourage maximal eort during each jump attempt.
All the testing was conducted at the basketball training facility prior to the start of strength
training sessions. The same standardized warm-up was performed before each testing session, which
included dynamic stretching and locomotion patterns (i.e., skipping, jogging, and running), and
was similar to that of previous literature [
17
,
18
,
26
]. Movement intensities gradually increased over
the warm-up duration to prepare subjects for maximal performance during the jump testing. CMJs
were performed on the commercially available ForceDecks FD4000 Dual Force Platforms hardware
(ForceDecks, London, UK) with a sample rate of 1000 Hz.
The commercially available ForceDecks software (ForceDecks, London, UK) was used to analyze
all the CMJs and generate the CMJ variables using conventional methods [
27
]. The ForceDecks software
uses a 20-N oset from the measured bodyweight, which was quantified before the jump, to define the
start of the movement. The end of the eccentric phase and start of the concentric phase was defined as
minimum displacement (absolute) which is equal to zero velocity, while take-owas defined as the
time point at which the total vertical force fell below the threshold of 20 N below bodyweight. Before
calculations were made, the ForceDecks Software combined the data from the two force transducers
(sum of the left and right force data). The software uses a 20-N oset from the measured bodyweight
obtained prior to the jump to define the start of movement. The end of the eccentric phase and start of
the concentric phase was defined as minimum displacement (absolute) which is equal to zero velocity,
while take-owas defined as the time point at which the total vertical force fell below the threshold of
20 N below bodyweight. All the asymmetry variables were computed via post hoc analysis following
the calculation of traditional CMJ metrics, which was similar to the methods reported in previous
literature [21].
Descriptions of the CMJ variables are outlined in Table 1. The variables included for analysis were
selected because they are part of the ForceDecks Software default asymmetry performance analysis
output, and may be of interest to practitioners. A multitude of variables were incorporated in the
analysis, because as previous literature has suggested, the most reliable variables may not be the most
ecacious in monitoring and detecting neuromuscular fatigue or changes in athlete performance [
18
].
Sports 2019,7, 103 5 of 15
Table 1. CMJ Variable Abbreviations and Definitions.
Variable Abbreviation Definition
Concentric Impulse (Ns) ConcImp Concentric force exerted multiplied by time taken
Concentric Impulse 50ms (Ns) ConcImp-50 Total net impulse over first 50-ms epoch of the
concentric phase
Concentric Impulse 100ms (Ns) ConcImp-100 Total net impulse over first 100-ms epoch of the
concentric phase
Concentric Mean Force (N) ConcMF Mean force during the concentric phase
Concentric Peak Force (N) ConcPF Peak force over the concentric phase
Eccentric Braking RFD (N/s) EccBrakRFD
Eccentric rate of force development from minimum
force at the start of the active braking phase to zero
velocity at the end of the eccentric phase
Eccentric Braking RFD-100ms (N/s) EccBrakRFD-100
Eccentric rate of force development over first 100-ms
epoch of the active braking phase
Eccentric Deceleration RFD (N/s) EccDecRFD
Eccentric rate of force development from maximum
negative velocity to zero velocity at the end of the
eccentric phase
Eccentric Mean Force (N) EccMF Mean force during the eccentric phase from start of
movement to zero velocity
Eccentric Peak Force (N) EccPF Peak force over the eccentric phase
Force at Peak Power (N) F@PP Force exerted at peak power
Force at Zero Velocity (N) F@0V Combined force when velocity is zero/minimum
displacement
Landing RFD (N/s) LandingRFD Rate of force development during the landing phase
Peak Landing Force (N) Peak Landing Force Peak force achieved during the landing phase
Positive Imp (Ns) PosImp Total net of positive impulse
Take-OPeak Force (N) TakeoPF Peak force over the entire take-ophase
2.3.1. Countermovement Jump with an Arm Swing (CMJ AS)
Subjects started in the tall standing position, with feet placed hip width to shoulder width apart,
but with hands free for movement. Then, the subject was instructed to start with equal weight
distribution on both force cells. A visual representation of weight distribution was displayed on a
monitor in front of the subject to provide synchronized and integrated feedback, allowing the subject
to adjust their positioning for equal quantities of body weight to be distributed on each force cell for
the start of the jump. Then, the subject dropped into the countermovement position to a self-selected
depth, incorporating an arm swing in their most natural, self-selected manner, followed by a maximal
eort vertical jump and landing in an athletic position on the force cells. The subject reset to the starting
position after each jump, and the procedure was completed for a total of three jumps. If at any point
the subject exhibited excessive knee flexion once airborne, the jump was ruled invalid and repeated.
2.3.2. Countermovement Jump with No Arm Swing (CMJ NAS)
In the same manner as the CMJ AS, subjects started in the tall standing position, with feet placed
hip width to shoulder width apart and hands akimbo. Then, the subject was instructed to start
with equal weight distribution on both force cells. A visual representation of weight distribution
was displayed on a monitor in front of the subject to provide synchronized and integrated feedback,
allowing the subject to adjust their positioning for equal quantities of body weight to be distributed on
each force cell for the start of the jump. Then, subjects dropped into the countermovement position to
a self-selected depth, followed by a maximal eort vertical jump, and landed in an athletic position on
the force cells. The subject would reset to the starting position after each jump, and the procedure was
completed for a total of three jumps. If at any point the subject removed their hands from their hips or
exhibited excessive knee flexion once airborne, the jump was ruled invalid and repeated.
2.3.3. Inter-Limb Asymmetry Calculation
While several options have been proposed to calculate lower limb asymmetry [
28
], the purpose of
the present analyses was to focus on the variability of the between-limb dierences; therefore, the main
Sports 2019,7, 103 6 of 15
concern was the absolute dierence between the lower limbs for each variable, and was calculated
as follows:
Lower-Limb Dierence Score = |(Right Left)|
2.4. Statistical Analysis
Data normality was confirmed by the Kolmogorov–Smirnov test, and the results are presented as
mean
±
SD. The intersession and intrasession mean and reliability were computed for each variable of
each limb, as well as for the Lower-Limb Dierence Score for each variable of the CMJ when performed
with an arm swing, as well as when performed without an arm swing. Relative reliability was
assessed using two-way mixed-eects and absolute agreement (3,1) intraclass correlation coecients
(ICC) [
29
]; furthermore based upon recommendations from prior literature, obtaining an ICC
0.70 was set as a minimum acceptable reliability [
18
,
19
,
21
,
30
]. In addition, absolute reliability was
assessed using coecient of variation (CV%) and a typical error of measurement (TE). Acceptable
absolute reliability was established at CV
10% [
18
,
19
,
21
]. Nevertheless, previous literature has
suggested that test reliability standards should ultimately be judged by the individual researcher or
practitioner based in accordance with their intended use, and that the most reliable variables may not
necessarily be the most ecacious in athlete monitoring and performance testing regimens [
18
]. The
typical error of measurement (TE) was calculated by dividing the standard deviation by the square
root of two to provide a reflection of the noise within the test caused by biological and technical
aspects [
31
]. In addition, Cronbach’s alpha was computed to assess and provide a measure of internal
consistency, allowing the present analysis to be compared with results that only determined Cronbach’s
alpha [
32
]. Lastly, based upon suggestions in previous work, the smallest worthwhile change (SWC)
was calculated as 0.2 X between-subject SD, and represented the smallest change that is of benefit for
athletic performance [
18
,
19
,
31
]. If the TE
SWC, the metrics were deemed capable of detecting the
SWC [18,19,31].
Two-way (Sex [Male versus Female]
×
Time [Test Session 1 versus Test Session 2]) repeated
measures analysis of variance (ANOVA) with Bonferroni post hoc pairwise comparison was used to
determine significant sex and time main eects and significant sex by time interactions within the
Lower-Limb Dierence Score of each variable. Additionally, two-way (Conditions [CMJ NAS versus
CMJ AS]
×
Time [Test Session 1 versus Test Session 2]) repeated measures ANOVA with Bonferroni
post hoc pairwise comparison was used to determine significant condition and time main eects and
significant condition by time interactions within the Lower-Limb Dierence Score of each variable.
Eects sizes (Cohen’s d) were calculated and interpreted as trivial (0–0.19), small (0.20–0.49), medium
(0.50–0.79), and large (0.80 and greater) [
33
]. SPSS (version 24, Armonk, New York) was used for all
the data analysis, with the alpha level set at p0.05.
3. Results
The results for intersession reliability are outlined in Table 2, while the results of intrasession
reliability are in Table 3. During the CMJ AS, 12 of the 16 variables met the acceptable criterion for
intersession relative reliability (ICC >0.70), and six of the 16 variables met the acceptable levels of
intersession absolute reliability (CV <10%). Additionally, 13 of the 16 variables met the acceptable
intrasession relative reliability, and 11 of the 16 variables met the acceptable criterion for intrasession
absolute reliability, during the CMJ AS. In addition, during the CMJ AS, only Concentric Peak Force,
Force at Peak Power, and Take-oPeak Force demonstrated TE SWC.
Sports 2019,7, 103 7 of 15
Table 2. CMJ Asymmetry Intersession Reliability During the CMJ AS and NAS.
Intersession Reliability
Arm Swing (CMJ AS) No Arm Swing (CMJ NAS)
CMJ Variable Mean ±SD Cron ICC SWC TE CV% Mean ±SD Cron ICC SWC TE CV%
Conc Imp (Ns) 263.0 ±25.5 0.973 0.747 12.89 18.03 9.1 242.2 ±14.5 0.987 0.868 8.44 10.22 6.1
Conc Imp-50ms (Ns) 44.0 ±4.7 0.980 0.800 2.28 3.32 11.2 48.3 ±4.6 0.984 0.839 2.32 3.24 9.9
Conc Imp-100ms (Ns) 91.0 ±9.7 0.978 0.786 4.74 6.87 11.3 97.0 ±8.0 0.986 0.854 4.34 5.64 8.7
Conc Mean Force (N) 916.6 ±52.6 0.989 0.879 32.76 37.23 5.8 878.4 ±45.2 0.992 0.909 31.11 31.99 5.3
Conc Peak Force (N) 1201.3 ±52.6 0.995 0.942 45.00 37.17 4.5 1084.8 ±58.3 0.992 0.911 41.24 41.21 5.4
Ecc Brak RFD (N/s) 2609.5 ±659.4 0.976 0.772 293.98 466.29 27.9 2578.4 ±618 0.982 0.823 293.17 436.98 26.7
Ecc Brak RFD-100ms (N/s) 2137.1 ±1238.5 0.834 0.296 338.03 875.75 58.1 1548.6 ±815.9 0.918 0.482 266.32 576.93 54.5
Ecc Dec RFD (N/s) 2945.3 ±802.1 0.981 0.851 395.93 567.15 32.3 3240.3 ±812.8 0.985 0.844 425.77 574.73 28.3
Ecc Mean Force (N) 442.3 ±37.1 0.956 0.644 13.43 26.21 8.4 441.4 ±30.1 0.972 0.744 12.97 21.25 6.8
Ecc Peak Force (N) 918.9 ±97.8 0.98 0.803 47.06 69.13 11.1 978.0 ±105.6 0.981 0.815 49.38 74.64 11.1
Force at Peak Power (N) 1096.2 ±47.2 0.995 0.940 39.09 33.38 4.4 958.8 ±47.5 0.991 0.901 30.51 33.58 5.0
Force at Zero Vel (N) 893.6 ±93.6 0.980 0.805 46.4 66.22 10.9 974.4 ±105.7 0.981 0.812 49.11 74.72 11.1
Landing RFD (N/s) 4,3754.7 ±1,4970.4 0.956 0.647 6350.06 10585.67 34 4,2511.3 ±1,3481.2 0.97 0.729 5895.85 9532.61 33.8
Peak Landing Force (N) 2524.4 ±514.3 0.970 0.730 218.77 363.64 20.7 2480.7 ±499.5 0.97 0.733 201.28 353.23 21.5
Positive Imp (Ns) 735.2 ±82 0.933 0.538 26.01 57.96 11.0 706.4 ±74.9 0.922 0.498 22.13 52.96 10.7
Take-OPeak Force (N) 1204.3 ±53.9 0.994 0.937 44.52 38.14 4.6 1086.9 ±58.4 0.992 0.911 41.36 41.3 5.4
*CMJ represents countermovement jump; AS represents arm swing; NAS represents no arm swing; SD represents standard deviation; Cron represents Cronbach’s alpha; ICC represents
intraclass correlation coecient; TE represents typical error; SWC represents smallest worthwhile change; CV% represents coecient of variation.
Sports 2019,7, 103 8 of 15
Table 3. CMJ Asymmetry Intrasession Reliability During the CMJ AS and CMJ NAS.
Intrasession Reliability
Arm Swing (CMJ AS) No Arm Swing (CMJ NAS)
CMJ Variable Mean ±SD Cron ICC SWC TE CV% Mean ±SD Cron ICC SWC TE CV%
Conc Imp (Ns) 263.0 ±19.7 0.964 0.817 12.76 13.94 7.1 242.1 ±13.1 0.979 0.886 8.45 9.25 5.5
Conc Imp-50ms (Ns) 44.0 ±4 0.967 0.832 2.28 2.84 9.6 48.3 ±4.1 0.974 0.863 2.32 2.91 8.9
Conc Imp-100ms (Ns) 91.0 ±8.4 0.962 0.809 4.74 5.92 9.7 97.0 ±7.1 0.978 0.932 4.34 5.00 7.7
Conc Mean Force (N) 916.6 ±47.9 0.979 0.884 32.81 33.84 5.3 878.4 ±41 0.986 0.923 31.14 29.01 4.8
Conc Peak Force (N) 1201.3 ±46.3 0.992 0.95 45.08 32.76 4.0 1084.8 ±54.3 0.985 0.918 41.28 38.39 5.1
Ecc Brak RFD (N/s) 2609.5 ±581.5 0.961 0.805 294.41 411.18 25.1 2578.4 ±548.5 0.971 0.849 293.65 387.86 23.9
Ecc Brak RFD-100ms (N/s) 2137.1 ±1112 0.771 0.363 333.66 786.3 52.0 1548.6 ±779.7 0.842 0.472 263.48 551.36 51.5
Ecc Dec RFD (N/s) 2945.3 ±684.6 0.971 0.851 396.59 484.07 27.3 3240.3 ±721.9 0.976 0.872 426.49 510.44 25.4
Ecc Mean Force (N) 442.3 ±36.7 0.906 0.615 13.45 25.95 8.3 441.4 ±29.8 0.940 0.726 12.99 21.09 6.7
Ecc Peak Force (N) 918.9 ±86 0.969 0.838 47.07 60.82 9.8 978.0 ±94.6 0.970 0.842 49.45 66.92 10.0
Force at Peak Power (N) 1096.2 ±43.6 0.991 0.948 39.16 30.84 4.1 958.8 ±40.8 0.987 0.925 30.56 28.87 4.3
Force at Zero Vel (N) 893.6 ±81.6 0.969 0.839 46.41 57.73 9.6 974.4 ±95 0.969 0.840 49.19 67.20 10.1
Landing RFD (N/s) 43754.7 ±1,2295.8 0.947 0.751 6347.75 8694.47 28.3 42511.3 ±1,1777.2 0.953 0.774 5899.38 8327.73 29.9
Peak Landing Force (N) 2524.4 ±465.5 0.953 0.772 218.97 329.16 19.2 2480.7 ±459.6 0.952 0.768 201.66 325.02 19.9
Positive Imp (Ns) 735.2 ±77.6 0.874 0.538 26.04 54.89 10.3 706.4 ±71.3 0.868 0.523 22.14 50.39 10.2
Take-OPeak Force (N) 1204.3 ±47.5 0.991 0.947 44.59 33.58 4.1 1086.9 ±54.6 0.986 0.918 41.40 38.62 5.1
*CMJ represents countermovement jump; AS represents arm swing; NAS represents no arm swing; SD represents standard deviation; Cron represents Cronbach’s alpha; ICC represents
intraclass correlation coecient; TE represents typical error; SWC represents smallest worthwhile change; CV% represents coecient of variation.
Sports 2019,7, 103 9 of 15
During the CMJ NAS, 14 of the 16 variables met the acceptable criterion for intersession relative
reliability (ICC >0.70), and six of the 16 variables met the intersession absolute reliability criterion (CV
<10%). Additionally, 14 of the 16 variables met the acceptable intrasession relative reliability, and 11 of
16 variables met the acceptable criterion for intrasession absolute reliability, during the CMJ NAS. In
addition, during the CMJ NAS, only the Concentric Mean Force, Concentric Peak Power, and Force at
Peak Power exhibited TE SWC.
There was a significant Sex X Time Interaction in lower-limb dierences for the total net of positive
impulse (PosImp) (p=0.005); however, tests of simple eects revealed no significant dierences
between sex at any time point (p>0.05), which was perhaps due to a small eect or small sample size.
There were no other significant Sex X Time Interactions (p>0.05) for any other variable; however,
there was a significant Sex main eect for dierences in the mean force during the eccentric phase from
start of movement to zero velocity (EccMF) between-limb asymmetry (Males =96.1
±
11.5 N; Females
=80.9
±
15.2 N; p=0.003). No significant sex dierences in the Lower-Limb Dierence Score of any
other variable were observed.
There was a significant Condition X Time Interaction [CMJ AS versus CMJ NAS X Testing Session
1 versus Testing Session 2] for the variable of the eccentric rate of force development over first 100-ms
epoch of the active braking phase (EccBrakRFD-100). A test of simple eects revealed no dierences
between conditions during Test Session 1 (CMJ AS =927.4
±
134.9 N/s; CMJ NAS =901.0
±
141.7 N/s;
p>0.05
), but a statistically significant dierence between condition during Test Session 2 (CMJ AS =
1469.5 ±274.2 N/s; CMJ NAS =776.1 ±158.5 N/s; p=0.003).
As outlined in Table 4, there was a significant condition [CMJ AS versus CMJ NAS] eect, with
CMJ AS demonstrating a significant decrease, with a small eect, in lower-limb dierences in the
total net impulse over first 100-ms epoch of the concentric phase (ConcImp-100) (p=0.048;
d=0.40
.
Additionally, there was a significant decrease, all with small to medium eects, in lower-limb dierences
during the CMJ NAS in the eccentric rate of force development from minimum force at the start of
the active braking phase to zero velocity at the end of the eccentric phase (EccBrakRFD) (p=0.019;
d=0.40), EccBrakRFD-100 (p=0.019; d=0.45), eccentric rate of force development from maximum
negative velocity to zero velocity at the end of the eccentric phase (EccDecRFD) (p=0.036; d=0.46),
and force exerted at peak power (F@PP) (p=0.029; d=0.32). While not statistically significant, there
appeared to be a small to medium eect of jumping condition on dierences in lower-limb total net
impulse over the first 50-ms epoch of the concentric phase (ConcImp-50) (p=0.064; d=0.42), peak
force over the concentric phase (ConcPF) (p=0.067; d=0.48), and peak force over the entire take-o
phase (TakeoPF) (p=0.079; d=0.42). In addition, there was no significant time [Test Session 1 versus
Test Session 2] eect observed for any variable.
Table 4. Dierences in Inter-Limb Asymmetries During the CMJ AS compared to the CMJ NAS.
Variable CMJ AS CMJ NAS
Conc Imp (Ns) 14.5 ±9.0 15.2 ±6.4
Conc Imp-50ms (Ns) 3.7 ±1.7 4.4 ±2.1
Conc Imp-100ms (Ns) 6.5 ±3.2 7.8 ±3.2 *
Conc Mean Force (N) 50.6 ±28.2 54.8 ±22.3
Conc Peak Force (N) 47.0 ±27.5 60.1 ±32.4
Ecc Brak RFD (N/s) 507.1 ±289.2 393.4 ±199.0 *
Ecc Brak RFD-100ms (N/s) 1198.4 ±803.2 838.5 ±639.6
Ecc Dec RFD (N/s) 632.3 ±280.4 502.1 ±252.6 *
Ecc Mean Force (N) 57.3 ±30.0 48.5 ±19.8
Ecc Peak Force (N) 85.3 ±39.5 95.9 ±52.0
Force at Peak Power (N) 84.0 ±37.7 96.5 ±52.3
Force at Zero Vel (N) 46.7 ±26.3 38.4 ±25.2 *
Landing RFD (N/s) 13133.5 ±9472.6 11727.2 ±7779.9
Peak Landing Force (N) 547.3 ±277.8 490.3 ±196.5
Positive Imp (Ns) 100.4 ±52.5 94.1 ±37.3
Take-OPeak Force (N) 48.5 ±29.3 60.7 ±32.0
CMJ represents countermovement jump; AS represents arm swing; NAS represents no arm swing; Data presented
as mean ±standard deviation; * represents p<0.05.
Sports 2019,7, 103 10 of 15
4. Discussion
The purpose of the present study was to establish the intrasession and intersession relative
and absolute reliability of variables obtained from a force plate used to quantitate lower extremity
inter-limb asymmetry during both the CMJ AS and CMJ NAS. A secondary purpose sought to identify
dierences in lower extremity inter-limb asymmetries during the CMJ AS compared to the CMJ NAS.
The major findings of the present study were (1) the majority of variables met the acceptable criterion
for intersession and intrasession relative reliability (ICC >0.70) during both CMJ protocols; (2) less than
half of the variables examined met the acceptable standard for intersession and intrasession absolute
reliability (CV <10%) during both CMJ protocols; (3) only three variables demonstrated the sensitivity
to detect the SWC (SWC >TE) during both CMJ protocols; and (4) it appears that the CMJ protocol has
an influence on the variability of lower extremity inter-limb asymmetries.
Previous literature evaluating lower extremity asymmetries have solely focused on outcomes
of the concentric phase of the CMJ. In the present study, the concentric force exerted multiplied by
time taken (ConcImp), ConImp-50, ConcImp-100, mean force during the concentric phase (ConcMF),
ConcPF, and TakeoPF all demonstrated adequate relative (ICC >0.800) and absolute reliability
(CV <10%). In parallel to the present study, Menzel et al. [
13
] tested the reliability of inter-limb
asymmetries during the CMJ. While not including an analysis of the eccentric phase, they evaluated
symmetries via the lateral symmetry index (LSI), which was calculated as ((value of right limb
value
of left limp/greatest value of both limbs)
×
100). Their findings included LSI =5.58%, 23.45%, and
20.66%, for ConcPF, F@PP, and ConcImp, respectively [
13
]. Additionally, Menzel et al. [
13
] reported
the relative reliability of the CMJ tests during the pilot testing of 16 soccer players (ICC: ConcPF =
0.74, Peak Power =0.81, and Impulse =0.71). Using a comparable asymmetries analysis, Benjanvatra
et al. [
16
] identified asymmetry values of ~7–9% for ConcMF, ~8–10% for ConcPF, and ~16–19% for
ConcImp, using the CMJ NAS. Meanwhile, Menzel et al. [
13
] reported similar findings to those of
the present study, improvements in both relative and absolute reliability in the present study may
relate to our analysis including basketball athletes, where jumping is a large component of their sport,
while the aforementioned studies included professional soccer players [
13
] and recreationally trained
subjects [16].
Similarly, the present findings support those of Newton et al. [
24
], which also reported asymmetries
of 5.68% in ConcPF and 6.28% in ConcMF, during the CMJ AS. Further corroborating the findings of
the present investigation, Impellizzeri et al. [
12
] examined the reliability of ConcPF during the CMJ
NAS, using the unique aforementioned protocol requiring only one force platform. When obtaining
an average of three jumps, Impellizzeri et al. [
12
] reported almost identical findings to that of the
present study (TE of 2.8% and an ICC =0.86). However, the present study adds to the literature by
identifying marginal improvements in both the relative and absolute reliability of ConcPF during the
CMJ AS when compared to the CMJ NAS, with increases in ICC values, as well as reductions in both
CV% and TE. Similarly, TakeoPF revealed a minor reduction in TE and CV% during the CMJ AS. In
contrast, it appears that a marginal improvement in reliability may emerge for ConcImp, ConImp-50,
ConcImp-100, and mean force during the concentric phase (ConcMF) during the CMJ NAS. Potential
dierences in the reliability between the CMJ AS and CMJ NAS may relate to the arm swing more
consistently aiding in peak performances captured in an instant or small epoch, such as ConcPF and
TakeoPF, while mild alterations in arm swing synchronization can exacerbate variability among
metrics that occur over a longer time frame, such as the total net of positive impulse (PosImp) and
ConcMF. In addition, it is important to note that although the present study observed similar inter-limb
reliability parameters in regard to ConcMF and ConcPF on average, this does not mean that these
metrics can be utilized interchangeably, as previous literature has noted a disagreement in side-to-side
dierences between the variables [34].
EccMF met the accepted reliability criterion during the CMJ NAS, but lacked adequate repeatability
during the CMJ AS, while the peak force over the eccentric phase (EccPF) met the relative reliability,
but fell just outside the absolute reliability standards established during both CMJ protocols. To our
Sports 2019,7, 103 11 of 15
knowledge, this is the first data to identify the reliability of inter-limb EccMF and EccPF during the
CMJ, as well as the first to measure the influence of the arm swing. Although variables obtained
from the eccentric phase of the CMJ have been implicated as important factors used in injury risk
analysis [
35
,
36
], the present data would suggest a limitation in using the traditional 10% rule [
7
9
] if
EccPF was a variable of interest. Therefore, future literature should build upon the present analysis to
evaluate the magnitude of alteration in eccentric components following both acute and chronic fatigue
and following injury.
Currently, there is limited evidence assessing the reliability of inter-limb force parameters during
the CMJ, with even less specifically identifying the reliability of variables beyond the concentric
phase. However, previous literature has examined the reliability of the SLCMJ. Recent work by
Bishop et al. [
14
] examined inter-limb asymmetries in ConcPF and eccentric impulse, as well as
concentric impulse during the SLCMJ. Their data illuminate asymmetries ranging from 1.6% to 3.4%,
and intra-limb ICC values >0.800 and CV =3.3–5.8% [
14
]. These findings corroborate the present data,
suggesting that both eccentric and concentric phases yield variables meeting acceptable reliability
standards. Similar in the exploration of SLCMJ reliability, data published by Hopper et al. [
37
] reported
a high repeatability (ICC =0.92) of within-limb flight time during the SLCMJ. More recently, McElveen
et al. [
38
] has also identified a high level of within-limb relative reliability (ICC =0.850–0.950) of
various metrics during the SLCMJ. Similarly, the single leg hop test can be used to assess lower-limb
asymmetries. Auggustsson et al. [
39
] reported values of ICC =0.98 and CV =2.5% during a single
leg hop protocol comparing the maximal hop length. While these studies examined within-limb
reliability, the paralleling inter-limb reliability identified by the present study during the CMJ reinforces
previous findings.
Additionally, in accordance with previous literature examining the traditional combined
lower-limb analysis, both F@PP and force at zero velocity—the combined force when velocity
is zero/minimum displacement (F@0V) met the acceptable criterion for reliability during both
protocols [
20
,
21
]. However, PosImp fell just outside the acceptable reliability criterion, and the
peak force achieved during the landing phase (Peak Landing Force) lacked reliability during the CMJ
AS or the CMJ NAS.
As expected, EccBrakRFD, EccBrakRFD-100, EccDecRFD, and the rate of force development during
the landing phase (LandingRFD) variables demonstrated poor relative and absolute reliabilities during
both CMJ protocols. These findings are in parallel with previous literature, which has consistently
documented “rate” variables as unreliable (CV =16–50%) [
19
,
21
,
40
,
41
]. Although the present study
used the common recommendation of 1000 Hz, which was thought to be adequate, an increase in
the sampling rate may improve the reliability of the RFD indices, while other factors may influence
the reliability of the eccentric phase, such as countermovement depth and velocity. Despite the lack
of reliability in the present study, RFD parameters have been regarded as vital components in a
variety of sports [
15
,
41
]. Therefore, future literature may explore increasing the sampling rate in an
attempt to improve the reliability of these measures, especially if deemed imperative in the clinical and
practical settings.
During the CMJ AS, only ConcPF, F@PP, and TakeoPF demonstrated TE
SWC. In contrast,
during the CMJ NAS, only ConcMF, ConcPF, and F@PP exhibited TE
SWC. These findings have
practical significance, as practitioners should select a CMJ protocol that optimizes the sensitivity of
detecting change among the variables they have established as key performance indices for their player
assessment and athlete monitoring strategies.
In general, CMJ NAS performance appeared marginally more reliable than the CMJ AS protocol,
which may seem surprising, as the CMJ AS is likely more common during sport play, and therefore
may be expected to improve familiarity and subsequent repeatability. However, previous literature
has observed similar improvements in reliability during CMJ NAS compared to the CMJ AS in other
sports requiring high jumping frequency, such as volleyball [
42
] and basketball [
21
]. These findings
Sports 2019,7, 103 12 of 15
likely indicate that the high degree of sport specificity and frequent repetitions during sport play does
not necessarily translate to improvements in reliability over CMJ NAS during testing.
There were no statistically significant dierences in the Lower-Limb Dierence Scores between
sexes, expect for EccMF, which was deemed trivial, as the dierence fell at or within the TE (TE: CMJ
AS =26.21 N; CMJ NAS =21.25 N). Therefore, the sex data was combined to increase the statistical
power of the primary analysis directed at examining dierences in lower-limb asymmetries between
jumping protocols. The present study identified a statistically significant Condition X Time Interaction
[CMJ AS versus CMJ NAS X Test Session 1 versus Test Session 2] for the variable of EcceBrakRFD-100.
However, this dierence is likely not practically significant, and alludes more to the large variability in
the metric, as it displayed an intrasession CV =52% during both CMJ protocols. The present study
observed no significant time eect [Test Session 1 versus Test Session 2], which may positively support
the reliability of the variables tested in the present study, as they were not statistically dierent from
one testing session to the next.
A novel finding of the present study was the influence of CMJ protocol on lower-extremity
dierence scores, as there was a significant condition eect [CMJ AS versus CMJ NAS] with a dierence
in the lower-extremity dierence score between jump protocols for the variables of ConcImp-100,
EccBrakRFD, EccDecRFD, and F@0V. While not reaching statistical significance, which was likely
due to the small sample size of the present study generating a lack of statistical power, there was
also a small to medium eect between jumping conditions for the variables of ConcImp-50, ConcPF,
and TakeoPF. Interestingly, eccentric associated variables appeared to demonstrate a reduction in
asymmetry during the CMJ NAS, while concentric variables appeared to demonstrate a reduction in
asymmetry during the CMJ AS. These findings suggest that the arm swing influenced CMJ symmetry
during the loading phase, but improved asymmetry during propulsion. To the best of our knowledge,
there is no previous literature comparing the influence of CMJ protocol on lower-limb asymmetries.
Therefore, it is not possible to make a meaningful comparison with previous literature. Regardless,
these findings may be relevant and beneficial in guiding coaches and practitioners in selecting a CMJ
protocol, once they have established the key performance indices within their athlete monitoring and
player assessment strategies.
The present study lays the foundation for utilizing the CMJ to provide quantitative data to guide
return-to-play and return-to-performance protocols following injury. While previous literature has
suggested the 10% rule, the present analysis has identified reliable metrics associated with both the
concentric and eccentric phases of the CMJ that may prove valuable in enhancing the rehabilitation
framework. Interestingly, the authors would like to note that it is plausible that inter-limb variability in
asymmetry may be positive, because during injury, it is likely that an athlete would select a movement
strategy that would avoid force application to the injured limb, likely manifesting in a consistent
asymmetry. Future work should build upon the present findings, characterizing alteration in force
outputs during both the concentric and eccentric loading phases of the CMJ following lower-limb injury.
The present study has limitations that warrant discussion. First, although training duration
was matched prior to Test Session 1 and Test Session 2, the training load was not monitored with
more advanced measures, such as internal or external load-monitoring strategies [
17
], which may
have improved the ability to specifically match basketball-specific training loads prior to testing.
Secondly, the present study examined a relatively homogeneous sample of skilled jumpers with
limited between-subject variability, which may have contributed to a reduction in relative reliability.
Additionally, it should be recognized that the most reliable measures may not be the most ecacious
in monitoring changes in fatigue and performance or assessing injury risk parameters. As suggested
by previous literature, sport scientists and practitioners ultimately decide upon acceptable reliability
criterion and deem a variable that is reliable enough for its intended use [
18
]. Future research should
examine the sensitivity and specificity of the various CMJ asymmetry variables to detect change
following fatigue and injury to establish the key performance indices that are useful to clinicians, as
well as sports performance practitioners.
Sports 2019,7, 103 13 of 15
5. Conclusions
In conclusion, the findings of the present study oer key practical applications for assessing and
monitoring asymmetries in athlete performance. Both the CMJ AS and CMJ NAS provide reliable
information with respect to inter-limb asymmetries, suggesting that the CMJ may be a useful tool for
performance practitioners and clinicians to eectively monitor the changes associated with performance
and injury risk, as well as return-to-play and return-to-performance strategies. Additionally, it appears
that the CMJ protocol influences inter-limb asymmetries; therefore, the CMJ testing protocol should be
chosen in order to optimize the reliability of the variables of interest to the sport scientist, clinician,
or practitioner.
Author Contributions: Conceived and designed the experiments: A.H., B.D.; Performed the experiments: A.H.,
B.B., B.D.; Data Analysis: A.H., B.B., R.M.; Original Draft Preparation: A.H.; Writing—Review & Editing: B.B.,
B.D., E.F., R.M., M.B.; Visualization: A.H., R.M., E.F.; Supervised the project and project administration: B.D., M.B.
Funding: This research received no external funding.
Acknowledgments:
The authors thank the Men’s and Women’s Basketball Programs at the University of Oklahoma
for their continued support of research directed at enhancing athlete performance, while also improving overall
student-athlete welfare. The authors would also like to thank all of the student-athletes that volunteered their time
to participate in this study. Finally, the authors would like to thank Patrick Geha for his assistance with this project.
Conflicts of Interest: The authors declare no conflict of interest.
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2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
... Therefore, it is not surprising that force platforms continue to be recommended for obtaining more comprehensive information of CMJ performance [1,6]. Another potential advantage of a special type of force platforms, known as bilateral or dual force platforms, is that they discriminate the force produced by each leg during bilateral jumps [7]. The possibility to selectively assess the force exerted by each leg during bilateral jumps has allowed sport scientists to explore inter-leg asymmetries [8,9], this metric being a rich source of research due to its potential applications to improve sports performance and reduce the risk of injury [10][11][12]. ...
... The jump initiation in the CMJ is typically identified as the time point in which the vGRF falls below a given threshold (e.g., 10 N below body weight) [18,19]. In this regard, some authors have considered the total body weight (i.e., the sum of the vGRF of both force platforms) to select the same time point of jump initiation for both legs [7,16], while other authors have analysed the vGRF data of each force platform independently being possible to determine a different jump start for each leg [13]. Therefore, considering the limited reliability of inter-leg asymmetries variables reported in previous studies [13,14], it seems important to identify the procedure of analysis that allows obtaining the single-leg mechanical performance variables with the greatest consistency. ...
... The effect of the jump start detection for each leg (simultaneous or independent) when analysing the force-time signal during bilateral CMJs performed on dual force platforms was also examined in the present study. An analysis of the literature reveals that there is no consensus regarding which is the most appropriate procedure of analysis [7,13,16]. We hypothesised that the Synchronous procedure would provide a greater reliability than the Asynchronous procedure due to the lower influence for the Synchronous procedure of the distribution of the weight between the two force plates during the weighing phase. However, contrary to our hypothesis, the Synchronous procedure did not provide any variable with a greater reliability than the Asynchronous procedure. ...
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Background The possibility to selectively assess the force exerted by each leg during bilateral jumps has allowed sport scientists to explore inter-leg asymmetries, this metric being a rich source of research due to its potential applications to improve sports performance and reduce the risk of injury. The purpose of this study was to explore the reliability and agreement of single-leg mechanical performance and inter-leg asymmetry variables obtained by two procedures of analysis (Synchronous [simultaneous jump detection for both legs] and Asynchronous [specific jump detection for each leg]) during bilateral countermovement jumps (CMJs). Method During a single testing session, 74 participants performed 5 maximal height bilateral CMJs on dual force platforms (Kistler, model 9260AA6, Winterthur, Switzerland), and the 2 trials that differed the least in terms of squat depth and jump height were considered for statistical analyses. The following mechanical variables were calculated separately for each leg using the Synchronous and Asynchronous procedures: mean force, peak force, and propulsive impulse. Results The procedures showed comparable reliability, except for mean force and propulsive impulse of the left leg (higher for the Asynchronous procedure). The agreement between the procedures was very high, while the most reliable mechanical variable was mean force (CV≈2.9%, ICC≈0.98), followed by peak force (CV≈4.4%, ICC≈0.96) and propulsive impulse (CV≈6.4%, ICC≈0.91). Reliability of inter-leg asymmetries was greater using mean and peak force (ICC range=0.74–0.82) than using propulsive impulse (ICC range = 0.65–0.66). Significance Both Synchronous and Asynchronous procedures can be used to evaluate single-leg mechanical performance (mean force, peak force, and propulsive impulse) and asymmetries, whereas mean force should be used to evaluate single-leg mechanical performance and mean or peak force to assess asymmetries.
... Athletes' CMJ's performance to measure lower body explosive power is well researched (Eagles et al. 2015). Previous studies have highlighted inter-limb asymmetry when athletes return from lower limb injury from soccer (Hart et al. 2019), basketball (Heishman et al. 2019) and youth elite team-sports athletes (Fort-Vanmeerhaeghe et al. 2020). A CMJ performance on force platforms is regarded as the benchmark for test accuracy to measure lower-body power (Requena et al. 2012). ...
... at RTP compared with baseline, which indicates a good rehabilitation outcome as asymmetry is usually present after lower limb injuries. Studies have shown that asymmetry is relevant and does exist when players RTP(Fort-Vanmeerhaeghe et al. 2020;Hart et al. 2019;Heishman et al. 2019). Recently ...
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Background: Medical professionals working in an elite sport environment have the challenging task to balance the athlete’s readiness to return to the playing field after severe injury with other stakeholders’ (coaches, sponsors, teammates) opinions and objectives. Objectives: Our study aimed to evaluate differences in the physical profiles of elite rugby players at return to play (RTP) after a severe knee injury, compared with their pre-injury profiles and matched controls. Method: Before the injury, participants performed four performance tests during their preseason screening. These tests were repeated and compared to baseline once a player was declared fit to play. Results: Significant differences (p ≤ 0.05) were found in the injured players’ group who were slower over 10 m speed, in their decision-making time and the total time of the reactive agility tests at RTP, whilst controls were significantly faster over 10 m and 30 m speed tests. The countermovement jump outcomes showed significant improvement in the uninjured participants (p ≤ 0.05). Conclusion: Our study highlights that injured players’ running speeds and decision-making times are slower after injury. The uninjured players have a positive outcome to training and match stimulus by improving their running speed and lower body explosive power during the season. Clinical implications: Our study provides insight into the RTP profile of elite rugby players, and a novel finding was the decision-making time deficit. This highlights the importance of cognitive training during injury rehabilitation as athletes make numerous decisions in a pressured and uncontrolled environment during a match. Speed training development is recommended as the athletes were slower after severe knee injury.
... Similar to strength, a wide variety of jumping tasks can assess inter-limb asymmetries. For example, countermovement jumps (CMJ) (7,34), drop jumps (45) and a variety of horizontal hopping (continuous unilateral jumping) tasks (13,16) have all been previously employed, each of which has shown acceptable reliability data both bilaterally and unilaterally (ICC = 0.68-0.99; CV = 2.82-9.18) in a number of studies (9,13,14,16). ...
Article
The aim of this brief narrative review is to summarize the present evidence, provide recommendations for data analysis, and appropriate training methods to reduce strength and power asymmetries within athlete populations. Present evidence shows that a strong interest in the assessment of asymmetry exists. Despite the perceived associated relationship between asymmetry and injury and performance, a clear link is still missing. Practitioners need to be aware of this when they decide to assess asymmetries and later design training interventions. Several bilateral and unilateral tests could be used to assess asymmetries such as isokinetic dynamometry, the isometric mid-thigh pull, squat and Nordic hamstring exercise. Based on the current evidence, future investigations require further standardization of methodology and analysis to optimize interpretation (e.g., within session and between session), adoption, and implementation of inter-limb asymmetry testing and appropriate interventions. In this review three training interventions have been proposed to reduce existing lower limb asymmetries in sport populations: traditional resistance training, flywheel resistance training, and combined training interventions, with some evidence suggesting such interventions can reduce lower limb asymmetries. Nonetheless, the number and quality of articles currently available are too limited to draw firm conclusions, therefore, further research is needed to verify whether training interventions can achieve these aims. To develop an understanding and application of interventions addressing inter-limb asymmetries within the sport, greater methodological rigor should be applied towards study design, data analysis and interpretation of future investigations as well as when appraising the current literature.
... Similarly, asymmetry in the pattern of movement is presented as a factor in increasing the risk of injury. Measuring asymmetry and explosiveness is also useful for assessing and directing an athlete returning to the training process after a rehabilitation process [22]. Asymmetry can be explained as the continuity of overload on one side of the body or muscle imbalance that occurs if it is not adequately compensated. ...
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Analyzing asymmetry from biomechanical parameters of the lower extremities has be�come a standard practice for accurate assessment of athletic performance, injury prevention, and rehabilitation. The aims of this study were (1) to determine differences between explosive strength and asymmetry of the lower extremities using kinetic parameters of the CMJ jump test in young female athletics, and (2) to investigate correlation between speed and asymmetry, as speed and kinetic parameters. The two groups of nine female sprinters (mean ± SD; G1-age 15.6 ± 1.34 years, height 170.1 ± 0.57 cm, body mass 62.54 ± 7.73 kg, and BMI 21.6 ± 2.05; G2-age 16.2 ± 1.3 years, height 168.4 ± 0.61 cm, body mass 57.69 ± 3.12 kg, and BMI 20.37 ± 1.38) performed the CMJ test without using an arm swing, as well as a 100 m test. Two tensiometric platforms were used for the kinetic parameters and asymmetry. Asymmetry was calculated by an AI equation, and the values of the takeoff velocities and jump height parameters were obtained by integral formula and the trape�zoidal rule of impulse-momentum methods. The results show differences in four kinetic parameters: height (G1- 26.82 ± 3.56 cm, vs. G2- 17.45 ± 2.01 cm), concentric impulse, (G1- 96.05 ± 16.95 N·s, vs. G2- 68.41 ± 4.77 N·s), takeoff velocity, (G1- 2.29 ± 0.14 m/s, vs. 1.83 ± 0.12 m/s), and concentric velocity, m/s (G1- 1.5 ± 0.175 m/s, vs. 1.17 ± 0.122 m/s), as well as a negative strong and very strong correlation between asymmetry and kinetic parameters for three parameters: Peak Force (G1- r = −0.878, and all subjects r = −0.633), Eccentric Impulse of left leg (G1- r = −0.865) and Concentric Impulse of right leg (G2- r = −0.878), (p <.05). The younger sprinters did not show the principle of muscle activation in the form of a longer preparatory phase of contact time, eccentric and concentric phase, as well as a force impulse that is optimal. There was no correlation between asymmetry and sprint performance
... The participants were positioned on the plate in an upright hip wide stand and the hands holding on the hips to prevent any acceleration impulse during the movement. Starting on command, the participants were asked to bend their knees and hips to a personal choice (Heishman et al., 2019). Reaching the individual deepest position, the participants were asked to jump as explosive and high as possible. ...
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Knee extension and hip flexion range of motion (ROM) and functional performance of the hamstrings are of great importance in many sports. The aim of this study was to investigate if static stretching (SS) or vibration foam rolling (VFR) induce greater changes in ROM, functional performance, and stiffness of the hamstring muscles. Twenty-five male volunteers were tested on two appointments and were randomly assigned either to a 2 min bout of SS or VFR. ROM, counter movement jump (CMJ) height, maximum voluntary isometric contraction (MVIC) peak torque, passive resistive torque (PRT), and shear modulus of semitendi-nosus (ST), semimembranosus (SM), and biceps femoris (BFlh), were assessed before and after the intervention. In both groups ROM increased (SS = 7.7%, P < 0.01; VFR = 8.8%, P < 0.01). The MVIC values decreased after SS (-5.1%, P < 0.01) only. Shear modulus of the ST changed for-6.7% in both groups (VFR: P < 0.01; SS: P < 0.01). Shear modulus decreased in SM after VFR (-6.5%; P = 0.03) and no changes were observed in the BFlh in any group (VFR =-1%; SS =-2.9%). PRT and CMJ values did not change following any interventions. Our findings suggest that VFR might be a favorable warm-up routine if the goal is to acutely increase ROM without compromising functional performance .
... The participant was asked to get into an upright hip-wide standing position on the plate. On command, the participant was asked to make a downward movement while bending their knees and hips to a position of personal choice (Heishman et al. 2019). After reaching the individual deepest position, the participant was instructed to jump as explosively and as high as possible. ...
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Foam rolling (FR) is a common intervention used as a warm-up to increase the range of motion (ROM) of a joint, without changes in subsequent performance. It has been shown that, in similar techniques (e.g., stretching), an additional intense warm-up can lead to performance potentiation. However, to date, it is not clear if this also holds true for FR, and if this effect is similar in both sexes. Thus, the purpose of this study was to compare the effects of an intense warm-up either before or after FR with the effects of FR without any additional intense warm-up, in both females and males. In total, 27 volunteers (14 male, 13 female) visited the laboratory on three separate days. Each participant was randomly assigned to one of the three interventions. ROM was assessed with a Sit n' Reach box, and countermovement jump (CMJ) height with a force plate, both before and after the interventions. In addition, maximum voluntary isometric contraction (MVIC) peak torque and maximum voluntary dynamic contraction (MVDC) peak torque were assessed with a dynamometer. ROM increased to the same extent following the interventions in all groups, with a large magnitude of change (P < 0.001; d = 1.12 to 1.83). In addition, male participants showed significantly higher increases in ROM when the intense warm-up was performed after FR (P < 0.001; d = 1.44), but not without the intense warm-up (P = 0.45; d = 0.57) or when the intense warm-up was performed before FR (P = 0.24; d = 0.69). No significant changes in CMJ height, MVIC peak torque, or MVDC peak torque were observed (P > 0.05). We therefore conclude that the time-efficient athlete might skip further intense warm-up, besides FR, when the goal is to increase ROM and to sustain performance parameters.
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Lum, D, Joseph, R, Ong, KY, Tang, JM, and Suchomel, TJ. Comparing the effects of long-term vs. periodic inclusion of isometric strength training on strength and dynamic performances. J Strength Cond Res XX(X): 000-000, 2022-This study compared the effects of including isometric strength training (IST) for consecutive 24 weeks (CIST) against a periodic inclusion (PIST) of this mode of training on strength and dynamic performances. Twenty-four floorball athletes (age: 23 6 2.7 years, stature: 1.74 6 2.08 m, and body mass: 72.7 6 14.4 kg) were randomly assigned to the control (CON), CIST, or PIST group. Athletes completed 20-m sprint, countermovement jump (CMJ), and isometric midthigh pull (IMTP) during pre-test and were tested on weeks 6, 12, 18, and 24. All groups performed a similar strength training program twice per week. However, 2 sets of squats were replaced with isometric squat in CIST for all 24 weeks but only on weeks 1-6 and 13-18 for PIST. A significant main effect for time was observed for 5-, 10-, and 20-m sprint time, CMJ height, peak force, peak power, time to takeoff , modified reactive strength index, IMTP peak force, relative peak force, and force at 200 milliseconds (p 5 ,0.001-0.037). Isometric strength training for 24 consecutive weeks resulted in greater improvement in 5-m sprint time than CON at week 24 (p 5 0.024, g 5 1.17). Both CIST and PIST resulted in greater improvements in 10-m sprint time than CON at various time points (p 5 0.007-0.038 and 0.038, g 5 1.07-1.44 and 1.18, respectively). Isometric strength training for 24 consecutive weeks and PIST resulted in greater improvements in 20-m sprint time than CON at week 6 (p 5 0.007 and 0.025, g 5 1.65 and 1.40, respectively). The results showed that the inclusion of IST resulted in greater improvements in sprint performance than CON but no significant difference in all measured variables with PIST.
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Lum, D, Joseph, R, Ong, KY, Tang, JM, and Suchomel, TJ. Comparing the effects of long-term vs. periodic inclusion of isometric strength training on strength and dynamic performances. J Strength Cond Res XX(X): 000-000, 2022-This study compared the effects of including isometric strength training (IST) for consecutive 24 weeks (CIST) against a periodic inclusion (PIST) of this mode of training on strength and dynamic performances. Twenty-four floorball athletes (age: 23 ± 2.7 years, stature: 1.74 ± 2.08 m, and body mass: 72.7 ± 14.4 kg) were randomly assigned to the control (CON), CIST, or PIST group. Athletes completed 20-m sprint, countermovement jump (CMJ), and isometric midthigh pull (IMTP) during pre-test and were tested on weeks 6, 12, 18, and 24. All groups performed a similar strength training program twice per week. However, 2 sets of squats were replaced with isometric squat in CIST for all 24 weeks but only on weeks 1-6 and 13-18 for PIST. A significant main effect for time was observed for 5-, 10-, and 20-m sprint time, CMJ height, peak force, peak power, time to take-off, modified reactive strength index, IMTP peak force, relative peak force, and force at 200 milliseconds (p = <0.001-0.037). Isometric strength training for 24 consecutive weeks resulted in greater improvement in 5-m sprint time than CON at week 24 (p = 0.024, g = 1.17). Both CIST and PIST resulted in greater improvements in 10-m sprint time than CON at various time points (p = 0.007-0.038 and 0.038, g = 1.07-1.44 and 1.18, respectively). Isometric strength training for 24 consecutive weeks and PIST resulted in greater improvements in 20-m sprint time than CON at week 6 (p = 0.007 and 0.025, g = 1.65 and 1.40, respectively). The results showed that the inclusion of IST resulted in greater improvements in sprint performance than CON but no significant difference in all measured variables with PIST.
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Previous research has sought to establish the relationship countermovement jump (CMJ) performance has with clubhead velocity (CHV). However, these investigations either assessed lower skilled golfers, or utilised field-based protocols, which are unable to assess a number of biomechanical variables. Fifty highly skilled golfers performed CMJs on Kistler force platforms in laboratory conditions. The CMJ variables included positive impulse, net impulse, average power, peak power, peak force, force at zero velocity and jump height. Clubhead velocity was measured using a TrackMan 3e launch monitor at a driving range. A Pearsons correlation was employed to measure the strength and direction of the relationships between CHV and CMJ derived performance variables. Results indicated strong positive relationships (all p's <0.001) between CHV and positive impulse (r = 0.695), net impulse (r = 0.689), average power (r = 0.645), peak power (r = 0.656), peak force (r = 0.517) and force at zero velocity (r = 0.528) with no significant relationship with jump height. However, if investigators only have access to field-based protocols, it is recommended that they measure jump height and utilise inverse dynamics to calculate take-off velocity. By multiplying take-off velocity by mass, this allows the attainment of net impulse.
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Heishman, AD, Daub, BD, Miller, RM, Freitas, EDS, Frantz, BA, and Bemben, MG. Countermovement jump reliability performed with and without an arm swing in NCAA Division 1 intercollegiate basketball players. J Strength Cond Res XX(X): 000-000, 2018-The countermovement jump (CMJ) is routinely used in athlete performance to quantify adaptions to training, as well as monitor neuromuscular readiness and fatigue. However, controversy remains in whether to incorporate an arm swing during the CMJ (CMJ AS) or keep the hands placed on the hips (CMJ NAS). Incorporating the arms provides a higher degree of sport-specificity that may yield improved reliability, especially in skilled jumpers. By contrast, the hands-on-hips approach isolates lower extremity force production and eliminates potential arm-swing variation. Therefore, the purpose of this study was to establish the reliability of CMJ typical (CMJ-TYP), CMJ concentric alternative (CMJ-Conc-ALT), and CMJ eccentric alternative (CMJ-Ecc-ALT) variables obtained during the CMJ AS and CMJ NAS. Twenty-two (men = 14, women = 8) NCAA Division 1 collegiate basketball players performed 3 CMJ AS and 3 CMJ NAS on a force plate, in a randomized order. To assess the test-retest reliability, participants returned 1 week later to perform 3 additional CMJ AS and 3 CMJ NAS. Intraclass correlation coefficient (ICC) and coefficient of variation (CV) were used to assess intersession and intrasession reliability for the various CMJ variables. A majority of CMJ-TYP and several CMJ-Conc-ALT and CMJ-Ecc-ALT variables exhibited adequate intersession and intrasession reliability (ICC > 0.700 and CV <10%) during both the CMJ AS and the CMJ NAS. Countermovement jump AS may provide more pertinent information about long-term changes in sport-specific performance, whereas the CMJ NAS may be more beneficial for detecting acute changes in neuromuscular fatigue and athlete readiness.
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The aim of this study was to assess agreement between peak and mean force methods of quantifying force asymmetry during the countermovement jump (CMJ). Forty-five men performed four CMJ with each foot on one of two force plates recording at 1,000 Hz. Peak and mean were obtained from both sides during the braking and propulsion phases. The dominant side was obtained for the braking and propulsion phase as the side with the largest peak or mean force and agreement was assessed using percentage agreement and the kappa coefficient. Braking phase peak and mean force methods demonstrated a percentage agreement of 84% and a kappa value of 0.67 (95% confidence limits: 0.45–0.90), indicating substantial agreement. Propulsion phase peak and mean force methods demonstrated a percentage agreement of 87% and a kappa value of 0.72 (95% confidence limits: 0.51–0.93), indicating substantial agreement. While agreement was substantial, side-to-side differences were not reflected equally when peak and mean force methods of assessing CMJ asymmetry were used. These methods should not be used interchangeably, but rather a combined approach should be used where practitioners consider both peak and mean force to obtain the fullest picture of athlete asymmetry.
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Inter-limb asymmetries have been shown to be greater during vertical jumping compared to horizontal jumping. Notable inter-limb differences have also been established at an early age in male youth soccer players. Furthermore, given the multi-planar nature of soccer, establishing between-limb differences from multiple jump tests is warranted. At present, a paucity of data exists regarding asymmetries in youth female soccer players and their effects on physical performance. The aims of this study were to quantify inter-limb asymmetries from unilateral jump tests and examine their effects on speed and jump performance. Nineteen elite youth female soccer players performed a single leg countermovement jump (SLCMJ), single, triple, and crossover hops for distance and a 20 m sprint test. Test reliability was good to excellent (ICC = 0.81-0.99) and variability acceptable (CV = 1.74-5.42%). A one-way ANOVA highlighted larger asymmetries from the SLCMJ compared to all other jump tests (p < 0.05). Pearson’s correlations portrayed significant relationships between vertical asymmetries from the SLCMJ and slower sprint times (r = 0.49-0.59). Significant negative relationships were also found between horizontal asymmetries during the triple hop test and horizontal jump performance (r = -0.47 to -0.58) and vertical asymmetries during the SLCMJ and vertical jump performance (r = -0.47 to -0.53). The results from this study highlight that the SLCMJ appears to be the most appropriate jump test for identifying between-limb differences with values ~12% showing negative associations with sprint times. Furthermore, larger asymmetries are associated with reduced jump performance and would appear to be direction-specific. Practitioners can use this information as normative data to be mindful of when quantifying inter-limb asymmetries and assessing their potential impact on physical performance in youth female soccer players.
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