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ASYMMETRY DETECTION HAS BEEN A TOPIC OF INTEREST IN THE STRENGTH AND CONDITIONING (SC) LITERATURE WITH NUMEROUS STUDIES PROPOSING MANY DIFFERENT EQUATIONS FOR CALCULATING BETWEEN-LIMB DIFFERENCES. HOWEVER, THERE DOES NOT SEEM TO BE A CLEAR DELINEATION AS TO WHICH EQUATION SHOULD BE USED WHEN QUANTIFYING ASYMMETRIES. CONSEQUENTLY, THE AUTHORS HAVE UNCOVERED 9 DIFFERENT EQUATIONS THAT POSE CONFUSION AS TO WHICH METHOD THE SC SPECIALIST SHOULD USE DURING DATA INTERPRETATION. THE AIM OF THIS ARTICLE IS TO IDENTIFY THE DIFFERENT EQUATIONS CURRENTLY BEING USED TO CALCULATE ASYMMETRIES AND OFFER PRACTITIONERS A GUIDE AS TO WHICH METHOD MAY BE MOST APPROPRIATE WHEN MEASURING ASYMMETRIES.
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Asymmetries of the Lower
Limb: The Calculation
Conundrum in Strength
Training and Conditioning
Chris Bishop, MSc,
1
Paul Read, PhD, CSCS*D,
2
Shyam Chavda, MSc, CSCS,
1
and
Anthony Turner, PhD, CSCS*D
1
1
London Sport Institute, Middlesex University, London, United Kingdom; and
2
School of Sport, Health and Applied
Science, St Mary’s University, London, United Kingdom
ABSTRACT
ASYMMETRY DETECTION HAS
BEEN A TOPIC OF INTEREST IN
THE STRENGTH AND CONDI-
TIONING (SC) LITERATURE WITH
NUMEROUS STUDIES PROPOS-
ING MANY DIFFERENT EQUA-
TIONS FOR CALCULATING
BETWEEN-LIMB DIFFERENCES.
HOWEVER, THERE DOES NOT
SEEM TO BE A CLEAR DELINEA-
TION AS TO WHICH EQUATION
SHOULD BE USED WHEN QUAN-
TIFYING ASYMMETRIES. CONSE-
QUENTLY, THE AUTHORS HAVE
UNCOVERED 9 DIFFERENT
EQUATIONS THAT POSE
CONFUSION AS TO WHICH
METHOD THE SC SPECIALIST
SHOULD USE DURING DATA
INTERPRETATION. THE AIM OF
THIS ARTICLE IS TO
IDENTIFY THE DIFFERENT EQUA-
TIONS CURRENTLY BEING USED
TO CALCULATE ASYMMETRIES
AND OFFER PRACTITIONERS A
GUIDE AS TO WHICH METHOD
MAY BE MOST APPROPRIATE
WHEN MEASURING ASYMME-
TRIES.
INTRODUCTION
The concept of asymmetries has
been the topic of numerous
research studies, some of which
have identified that such a phenome-
non is detrimental to performance
(4,10,12). Asymmetries in power
;10% have been shown to result in
a loss of jump height (4), and slower
change of direction speed times (12),
suggesting it would be beneficial
to minimize these differences. For such
a widely researched concept, it is sur-
prising that few studies have offered
a definition of this term. However,
Keeley et al. (16) propose that “Asym-
metrical strength across the lower
extremities can be defined as the inabil-
ity to produce a force of contraction
that is equal..” Although the majority
of studies refer to the differences
between limbs, it is important to under-
stand that this is not always the case.
Intralimb variations (differences within
the same limb) will be evident when
performing repeated athletic tasks
and are most likely magnified during
maximal efforts. Consequently, Exell
et al. (8) suggest that asymmetry can
only truly be classified as “real” if the
between-limb difference is greater than
the intralimb variation.
Typically, asymmetries have been re-
ported as a percentage with distinc-
tions being made between dominant
and nondominant, right and left, stron-
ger and weaker, or preferred and non-
preferred limbs. These distinctions
provide different “reference values,”
thus allowing asymmetries to be calcu-
lated for a given test or variable. How-
ever, the wide variety in such reference
values may have an effect on the result
being conveyed. For example, an ath-
lete may state that their right limb is
their dominant, but if scores are input-
ted into an equation using the stronger
and weaker classification, a different
score may be reported if the stronger
limb is not the dominant limb. Further-
more, if the stronger and weaker
method is used, data interpretation
over extended periods may lose con-
text particularly as higher scores can
change as a result of injury occurrence
(34). Consequently, the reference value
will have a profound effect on the
asymmetry result, emphasizing the
importance of distinguishing between
the different methods of calculations
noted in the body of available research
to date.
Thus far, relatively simple tests, such
as the back squat (9,11,23,30), coun-
termovement jumps (CMJ) (4,14,39),
Address correspondence to Chris Bishop,
C.Bishop@mdx.ac.uk.
KEY WORDS:
asymmetries; lower limb; equations;
symmetry angle
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Copyright ªNational Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
single-leg countermovement jumps
(6,15,16), and single-leg hops
(2,22,24,26,28,29), have proven to be
reliable and effective methods for de-
tecting asymmetries in the field. In
addition, laboratory-based tests, such
as the isometric squat or midthigh pull
(1,3,34) and isokinetic quadriceps and
hamstring testing (7,10,21), have also
been used to quantify between-limb
differences. In essence, it would seem
that the strength and conditioning
(SC) specialist can determine such dif-
ferences in a number of ways. More-
over, should practitioners wish to
calculate the level of asymmetry, the
test(s) chosen to do so will likely need
to retain specificity of both the sport-
ing needs analysis and the require-
ments of the athlete.
Although the validity and test-retest
reliability of different testing protocols
to measure asymmetry has been exam-
ined, what is less clear is which equa-
tion should be used when aiming to
quantify these differences. Since the
late 1980s (when interest in asymme-
tries first appeared to be published),
there have been a wide variety of
equations proposed in the literature
(5,20,25,27,31,32,35,38,40). In more
recent study methodologies, it be-
comes increasingly clear that some
“adopt” a specific equation purely by
citing from earlier literature. The num-
ber of variations in equations used
would indicate that further distinction
and understanding between them is
warranted. By doing so, this will allow
practitioners to ensure optimal validity
in their asymmetry calculations that
may have profound effects on program
prescription.
This review will provide the SC spe-
cialist with an overview of the different
equations that have been used to cal-
culate asymmetries to date. Where
possible, it will critically evaluate each
method in an attempt to provide prac-
titioners with some guidance and con-
sistency on the topic of asymmetry
detection moving forward.
EQUATIONS USED TO CALCULATE
ASYMMETRIES
To provide the reader with some con-
text as to how these equations differ,
a hypothetical example of jump height
is provided. In this instance, jump
height scores of 25 and 20 cm will be
used for each limb, making the
assumption that the larger score corre-
sponds to the dominant, right, and/or
stronger limb where appropriate
(Table). However, it should be noted
that the following example is purely
hypothetical and athlete scores will
not always follow this assumption. Fur-
thermore, each equation has been pro-
vided with an acronym by the authors.
This is because some studies have
referred to different equations by
the same name, thus differentiating
between each variation is necessary to
provide a clear distinction. Finally, the
authors stress that the reader should
address the Table carefully because
there are some very subtle differences
between some of the equations.
When referring to the asymmetry
score column, it is evident that there
is great disparity between the 9 identi-
fied methods. On first view, there is no
obvious choice between them, partic-
ularly if more than 1 equation brings
about the same score. However,
a deeper analysis of the asymmetry
Table
Different equations for calculating asymmetries (using hypothetical jump height scores of 25 and 20 cm)
Asymmetry name Equation Asymmetry score (%) Reference
Limb symmetry index 1 (LSI-1) (NDL/DL) 3100 80 Ceroni et al. (6)
Limb symmetry index 2 (LSI-2) (1 2NDL/DL) 3100 20 Schiltz et al. (31)
Limb symmetry index 3 (LSI-3) (Right 2left)/0.5 (right + left) 3100 22.2 Bell et al. (4); Marshall et al.
(20)
Bilateral strength asymmetry
(BSA)
(Stronger limb 2weaker limb)/stronger
limb 3100
20 Nunn et al. (25), Impellizzeri
et al. (14)
Bilateral asymmetry index 1
(BAI-1)
(DL 2NDL)/(DL + NDL) 3100 11.1 Kobayashi et al. (17)
Bilateral asymmetry index 2
(BAI-2)
{2 3(DL 2NDL)/(DL + NDL)} 3100 22.2 Wong et al. (38); Sugiyama
et al. (35)
Asymmetry index (AI) (DL 2NDL)/(DL + NDL/2) 3100 22.2 Robinson et al. (27); Bini and
Hume (5)
Symmetry index (SI) (High 2low)/Total 3100 11.1 Shorter et al. (32); Sato and
Heise, (30)
Symmetry angle (SA) (4582arctan [left / right])/9083100 7.04 Zifchock et al. (40)
DL 5dominant limb; NDL 5nondominant limb.
Asymmetries: The Calculation Conundrum
VOLUME 0 | NUMBER 0 | MONTH 2016
2
Copyright ªNational Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
literature does provide practitioners
with some indication of strengths
and weakness between the proposed
methods.
INTERPRETING THE EQUATIONS
The Table 1 shows that some equa-
tions produce the same asymmetry
result regardless of their differences,
thus some distinction is required to
guide the SC specialist through the
best way of determining between-
limb differences in performance. As
such, equations that produce the same
score have been grouped together for
further discussion.
LIMB SYMMETRY INDEX 1, LIMB
SYMMETRY INDEX 2, AND
BILATERAL STRENGTH
ASYMMETRY
The first method (limb symmetry
index 1, LSI-1) used by Ceroni et al.
(6) is actually a measure of limb sym-
metry rather than asymmetry. When
compared with LSI-2, the results,
although very different, are simply
a matter of which end of the “asym-
metry spectrum” is being calculated,
with the second focusing on asymme-
try levels for a given test. The bilateral
strength asymmetry (BSA) equation
used by Impellizzeri et al. (14) was
used as a method for calculating asym-
metries during a bilateral CMJ, and
although the equation is again slightly
different, the results will produce the
same level of asymmetry as LSI-1 and
LSI-2. However, there are potential
limitations in the BSA equation. The
result of always putting the stronger
scorefirstisthatpositivevalueswill
always be obtained which poses issues
surrounding longitudinal analysis.
There is the possibility that the stron-
ger limb could become weaker at
a later testing date, yet the criteria
used in this equation do not take this
into consideration. It is therefore the
suggestion of the authors that when
calculating asymmetries, dominant
and nondominant limbs are clearly
defined. Although dominant and non-
dominant limbs will still be subject to
changes in scores, those changes will
not affect which limb is the dominant
one for an athlete. Therefore, should
a lower score be obtained by the dom-
inantlimbinanygiventest,thiswillbe
reflected in a negative sign for the
asymmetry result. Consequently, con-
sidering the LSI-2 and BSA equations
produce the same asymmetry percent-
age, yet the former has provided
a more consistent distinction between
limbs, it is suggested that this method
may hold an advantage between the 2
when interpreting data scores.
LIMB SYMMETRY INDEX 3,
BILATERAL ASYMMETRY INDEX 2,
AND ASYMMETRY INDEX
Other comparable results are seen for
LSI-3, bilateral asymmetry index
(BAI)-2, and the asymmetry index
(AI). There are subtle differences in
each of the equations; however, once
again each one produces the same
asymmetry score. With that in mind,
it is perhaps only the LSI-3 equation
that practitioners could consider
removing as a calculation option. Bell
et al. (4) defined the asymmetry dis-
tinction between “right and left,”
which will produce the same result
as the other 2 options. However, some
sports such as fencing which are very
asymmetrical in nature (37), will most
likely dictate which leg is dominant in
key actions such as lunging; thus, this
distinction will provide more context
when reporting scores. Consequently,
it would seem plausible to use either
the BAI-2 or the AI should these equa-
tions be accepted for asymmetry
detection.
BILATERAL ASYMMETRY INDEX 1
AND SYMMETRY INDEX
These 2 equations produce substan-
tially smaller asymmetry scores than
any of the previously discussed meth-
ods. Once again, their use in more
recent studies would seem to be a by-
product of previously cited research as
opposed to identifying whether the
method itself is appropriate for the
required analysis or not. The symme-
try index (SI) only calculates asymme-
tries via the highest and lowest scores,
which again may be prone to change
depending on factors such as injury
history and exposure to training or
competition (33). Therefore, data col-
lected over extended periods could
result in the context of asymmetries
being lost if different limbs produce
the highest score. It is therefore the
suggestion of the authors that the
BAI-1 may hold an advantage over
the SI when calculating asymmetries.
However, similar to previous conclu-
sions, any comparison between the
BAI-1 and any previously suggested
methods requires further research and
is subject to the context in which these
equations are being used.
THE SYMMETRY ANGLE
This method of calculating asymme-
tries is somewhat different to all the
previously discussed equations. It
was first suggested by Zifchock
et al. (40) and provides a degree of
asymmetryawayfromanoptimal
angle of 458(Figure). This is created
when 2 values are plotted against
each other forming a vector in rela-
tion to the xaxis. Essentially, 2 iden-
tical values would create a 458angle
in relation to the xaxis and thus per-
fect symmetry (40). However, for
ease of interpretation, the result can
then be multiplied by 100 converting
it to a percentage, which is then com-
parable with all other equations (with
a score of 0% indicating perfect sym-
metry). Zifchock’s rationale for the
symmetry angle was that all other
methods require a “reference value”
of some sort and that this value is
dependent on the question being
asked. For example, if a comparison
between the stronger and weaker leg
is made, equations seem to have
adopted the stronger leg as the refer-
ence value—as per the equation used
by Nunn and Mayhew (25) and
Impellizzeri et al. (14). However, no
justification has been noted for this,
and if the weaker limb was chosen
as the reference value, asymmetry
scores would be different. Second,
a logical reference value may present
itself when determining scores for
injured populations or when a sport
has a clear dominant and nondomi-
nant side. However, healthy,
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Copyright ªNational Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
nonsporting populations pose no
clear limb to be used for this reference
value; therefore, a more robust
method for calculation is warranted
that can be applied to all scenarios.
Finally, asymmetry scores have been
seen to be “artificially inflated” again
because of an inappropriate reference
value being implemented into the
equation (40). It must be noted at this
point that should a logical reference
value (such as which limb is domi-
nant) exist, it may be that one of the
previously suggested asymmetry cal-
culations would be appropriate. Such
an example could be in sports such as
fencing, where the dominant limb will
always be considered to be the “lead
leg” because of the asymmetrical
nature of the sport (37).
Subsequently, Zifchock proposed that
the symmetry angle (SA) was immune
from these issues, thus proving to be
a more appropriate method for iden-
tifying asymmetries. However, it
should be acknowledged that the only
comparison drawn was against the
equation proposed by Robinson
et al. (27). At this point, should the
reasons in favor of the SA be accepted,
this would perhaps prove to be the
logical equation choice over all others
when attempting to calculate asym-
metries, and this is a notion that is
supported with recent studies (18,19).
PRACTICAL APPLICATIONS
The evidence presented would sug-
gest that the SA is the most apt
method for calculating asymmetries
moving forward. As the Table 1
shows, the SA result is substantially
smaller than all other equations—
remembering that the outcome is
immune to both reference values and
overinflated scores. Considering
asymmetries can be determined by
a vast array of exercises (as described
in the Introduction), the SA equation
can be easily implemented into data
analysis by all practitioners aiming to
monitor this characteristic. Conse-
quently,thedataanalysisinMicrosoft
Excel for this hypothetical example is
as follows:
Step1: 5DEGREESATAN20
25
538:66
Step2: ½45 238:66
90 3100 57:04%:
Typical assessments during physical
testing batteries include single-leg
countermovement jumps and single-
leg hops because of their ease of im-
plementation and associated low
cost. Thus, the SA could be easily
used to determine between-limb dif-
ferences during these commonly
used tests. Similarly, alternative
laboratory-based assessments such
as isometric midthigh pulls or even
strength exercises such as the back
squat can be accompanied by SA
data analysis, providing force plates
are accessible. As such, there would
seem to be no major limits to how
asymmetries are assessed and there-
fore no reason why the SA cannot be
used in the subsequent analysis. Fur-
thermore, the limited information
surrounding their effects on perfor-
mance would indicate that this is an
area that warrants further research.
Therefore, it is the suggestion of the
authors that practitioners consider
the SA as the chosen method when
calculating asymmetries during sub-
sequent data analysis and aim to
establish whether these functional
imbalances have a detrimental effect
on performance.
Finally, detecting change is a crucial
aspect of data analysis for SC practi-
tioners because this allows us to objec-
tively determine whether any noted
differences are true. There is a distinct
lack of research surrounding changes
in asymmetry scores over time and to
the authors’ knowledge, none using the
SA method. However, one method of
determining such differences in scores
(which can be applied in multiple data
analyses) is via the smallest worthwhile
change (13), which is the smallest
change in score that is accepted as
“real.” Assuming all data are reliable
(which will occur from a well-
Figure. Quantifying asymmetries via the symmetry angle method (figure taken from
the study by Zifchock et al. (40) and reprinted with permission from
Elsevier Publishing).
Asymmetries: The Calculation Conundrum
VOLUME 0 | NUMBER 0 | MONTH 2016
4
Copyright ªNational Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
designed protocol during 2–3 test tri-
als), the smallest worthwhile change
can be calculated by taking the
between-subject standard deviation
and multiplying it by 0.2 (36). It should
be noted that without multiple asym-
metry scores, a hypothetical example
cannot be provided here. However,
the principle of using the smallest
worthwhile change can be used when
assessing changes in asymmetry scores
for a group of athletes and will allow
for a true representation over an
extended period.
CONCLUSION
Judging by the number of recent
studies investigating asymmetries,
thiswouldseemtobeatopicof
interest in SC research. As with all
forms of testing, optimal validity
and reliability are essential so that
the SC specialist can have full confi-
dence when analyzing data and thus
make informed decisions toward
their athletes’ physical preparation.
To the authors’ knowledge, distin-
guishing between equations has not
yet been addressed or established;
therefore, it is difficult to completely
justify which method should be used
over another. However, the very lim-
ited research on this specific topic
may indicate that reporting asymme-
tries via the SA method holds some
advantages over other options. It
wouldseemtobeimmunetorefer-
ence values and inflated scores, which
may indicate it is a more robust
method for asymmetry detection in
all populations. In addition, the sim-
ilarities between all other equations
(refer to the Table) are noticeable,
with some having only a subtle differ-
ence in its methods for their respec-
tive calculations. Such similarities are
compounded when 2 or more equa-
tions yield the same score, providing
no clear choice between them. How-
ever, the importance of providing
clarity surrounding the issue of refer-
ence values would seem to be para-
mount and an equation that can be
applied to all circumstances that is
exempt to these issues may offer
a more consistent and universal
approach to asymmetry detection.
Conflicts of Interest and Source of Funding:
The authors report no conflicts of interest
and no source of funding.
Chris Bishop is
a strength and
conditioning
coach at the
London Sport
Institute, Mid-
dlesex University
where he is also
the Programme
Leader for the
MSc in strength and conditioning.
Paul Read is
a strength and
conditioning
coach and senior
lecturer in
strength and
conditioning at St
Mary’s
University.
Shyam Chavda
is a strength and
conditioning
coach and tech-
nical associate at
the London Sport
Institute, Mid-
dlesex University,
the lead coach for
the Middlesex
University weightlifting club, and an
assessor/tutor for British Weightlifting.
Anthony
Turner is the
director of post-
graduate pro-
grammes at the
London Sport
Institute, Mid-
dlesex University
where he is the
joint programme leader for the MSc in
strength and conditioning.
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Asymmetries: The Calculation Conundrum
VOLUME 0 | NUMBER 0 | MONTH 2016
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... Two different performance scores were used: (1) The CS was calculated in percentage (%) using the following formula: [CS = ((ANT + PL + PM)/3 × limb length) × 100] [25]. (2) The CS was used then to calculate the limb symmetry index (LSI) in percentage (%) using the following formula, commonly used for uninjured population: [LSI = (CS non-dominant/CS dominant) × 100] [28,29]. The limb symmetry index (LSI) is usually known as a measure for the level of symmetry in terms of physical or functional performance between the lower limbs [30]. ...
... Therefore, inter-limb symmetry is an adequate investigative method for detecting side-to-side differences in uninjured players. In addition, YBT scores have also been associated with an increased risk of injury to the lower limbs [32], such as CS ≤ 89% [8] and LSI ≤ 90% [6,28,30]. Therefore, the YBT is a useful tool for identifying players with greater DBP and accordingly with a lower risk of injury. [30]. ...
... Therefore, inter-limb symmetry is an adequate investigative method for detecting side-toside differences in uninjured players. In addition, YBT scores have also been associated with an increased risk of injury to the lower limbs [32], such as CS ≤ 89% [8] and LSI ≤ 90% [6,28,30]. Therefore, the YBT is a useful tool for identifying players with greater DBP and accordingly with a lower risk of injury. ...
Article
Full-text available
The ability to maintain a stable single-leg balance stance during a fast change of direction movement is a fundamental aspect both for improving sport-specific skills and for prevention strategies. The aim of this cross-sectional study was to investigate the associations between multidirectional speed performance (MDS), dynamic balance performance (DBP), and chronological age in young and uninjured soccer players. In addition, it was examined whether chronological age and balance can predict variance in speed performance. One-hundred forty-six young male soccer players (age range 11–19) performed the y-balance test (YBT) and the lower extremity functional test (LEFT). Descriptive statistics, Pearson correlation, and multiple regression analysis were executed. The analyses were carried out on the further variables: for the DBP, the YBT composite score % (CS dominant leg/CS non-dominant leg) and limb symmetry index % (LSI) were used; for the MDS, the LEFT time in seconds (s) was used. Findings revealed LEFT scores to have a significant association with chronological age (p = 0.000), CS dominant (p = 0.019) and LSI (p = 0.044) of the YBT. In addition, CS dominant and chronological age explained the variance of the LEFT by 44%, regardless of LSI. To conclude, MDS revealed a strong association with DBP of the dominant side but a small association with LSI. In addition, a small association was found between quick LEFT times and older players. Finally, MDS variance can be predicted from DBP of the dominant side and chronological age in young soccer players. The tests used in this study could be useful screening tools for the detection of performance deficits, the implementation of prevention training programs, and the optimization of selection strategies in soccer academies. Keywords: prevention; youth athletes; screening tests; y-balance test; lower extremity functional test; limb symmetry index; knee stability; change-of-direction speed; postural control
... Interlimb asymmetry has been defined as the difference in performance and function of one limb with respect to another (Bishop et al., 2016) and can be categorized into: anatomical, morphological, flexibility, strength, skill or outcome (Dos'Santos et al., 2021). There is an abundance of literature that has sought to characterize interlimb asymmetries . ...
... Previous asymmetry research using English players has revealed that interlimb asymmetries are an inherent characteristic when measured using a variety of testing protocols (Gonzalo-Skok et al., 2019;Bishop et al., 2021bBishop et al., , 2022a. Unlike investigations that show great variation in the methods used to calculate asymmetry (Bishop et al., 2016), recent research has consistently adopted the percentage difference method which facilitates the comparison of asymmetry magnitude across different investigations and populations. Importantly, the polarity of an asymmetry score calculated via this method allows the direction of asymmetry to be quantified and its use has shown that the 'dominant limb' rarely remains consistent for different asymmetry assessments and may change as a consequence of training or injury (Bishop et al., 2016;Dos'Santos et al., 2021). ...
... Unlike investigations that show great variation in the methods used to calculate asymmetry (Bishop et al., 2016), recent research has consistently adopted the percentage difference method which facilitates the comparison of asymmetry magnitude across different investigations and populations. Importantly, the polarity of an asymmetry score calculated via this method allows the direction of asymmetry to be quantified and its use has shown that the 'dominant limb' rarely remains consistent for different asymmetry assessments and may change as a consequence of training or injury (Bishop et al., 2016;Dos'Santos et al., 2021). To ensure consistency in the comparisons being made over repeated time points, previous asymmetry studies in soccer have preferred to compare the left and right limbs. ...
Article
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The aims of this study were: (1) to quantify interlimb asymmetries in EPL soccer players in the context of kicking limb preference and (2) to establish the relationship between interlimb asymmetries and measures of physical performance. Twenty-two players (age: 21.8 ± 4.4 years) from an EPL club performed a running gait assessment (20 km/h) and unilateral countermovement jumps, a CoD assessment (modified 505 test), and an isokinetic knee extension/flexion protocol using each leg. Asymmetries were quantified using the percentage difference method and Pearson's correlations were used to quantify the association between variables. Players displayed the greatest level of asymmetry in isokinetic strength measures (5.9–12.7%) and lower levels of asymmetry in gait (1.6–7.7%), jump (0.9–7.0%) and CoD (1.9–3.5%) assessments. The influence of the preferred kicking limb was most evident in the isokinetic assessment with the players showing dominance in the preferred limb for knee flexor strength and in the non-preferred limb for knee extensor strength. These manifested in the asymmetry values calculated for the hamstring:quadricep (H:Q) ratios at 60°/s (8.80 ± 7.82%) and 240°/s (11.22 ± 7.04%) and in the functional H:Q ratio (12.67 ± 8.25%). The asymmetry values for peak extensor moment at 240°/s showed a significant correlation (ρ = −0.55, p = 0.034) with 10 m time in the CoD assessment. These findings provide benchmark asymmetry data for soccer practitioners and reveal that kicking limb preferences may bring about interlimb differences in the H:Q ratio which raises important considerations in the design of testing batteries and injury reduction interventions.
... Currently, calculating inter-limb asymmetries requires custom MS Excel spreadsheets (Bishop et al., 2018a;Bishop et al., 2016). The interlimb R Stats package (v4.2.1; R Core Team 2022) is an open-source tool that helps researchers, rehabilitation specialists, and sports scientists effortlessly assess limb imbalances. ...
... Users can opt to use the package's primary function, interlimb(), which selects the most-appropriate asymmetry index, depending on testing modality (Bailey et al., 2021;Bishop et al., 2016). Advanced users, and those familiar with interlimb asymmetry research, can override the default selection via the asym.algo ...
Preprint
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Inter-limb asymmetries relate to increased incidence of injury and decreased athletic performance. Current methods of assessing inter-limb asymmetries requires custom MS Excel Spreadsheets. The interlimb R package provides an open-source alternative to assessing inter-limb asymmetry scores. This paper briefly explores inter-limb asymmetry mathematical models and their utilization, and outlines how users can generate asymmetry scores and reliability measures nearly instantaneously. Advanced users can extend the interlimb package by building data sets containing asymmetry scores from multiple indexes. Finally, users are shown how to track and plot changes in asymmetry scores relative to a baseline value and to the previous assessment.
... To identify asymmetry between limbs, the asymmetry index (ASI) was calculated using the following formula [33,34]: On each testing day, participants were instructed to perform a progressive test to determine the maximum power produced (based on familiarization results) of eight repetitions on each limb at maximum effort, starting with the weaker limb. The mean power of the best four repetitions of each set was recorded using a rotatory axis encoder (Chronojump Bosco-System, Barcelona, Spain) and associated Chronojump software (v. ...
... = almost perfect [32]. To identify asymmetry between limbs, the asymmetry index (ASI) was calculated using the following formula [33,34]: ...
Article
Full-text available
The purposes of this study were to quantify inter-limb asymmetries from unilateral jumps, change of direction (COD) speed, and flywheel resistance skill tests and to examine their relationship with physical performance in a sample of elite youth female basketball players. Eleven female basketball players (age = 17.56 ± 0.60 y; body mass = 75.13 ± 12.37 kg; height = 1.83 ± 0.08 m; BMI = 22.42 ± 2.28; sports experience = 6.31 ± 1.73 y; years post-peak height velocity = 4.79 ± 0.68 y) performed a battery of fitness tests in the post-season consisting of the Single Leg Countermovement Jump in vertical (SLCJ-V), horizontal (SLCJ-H), and lateral (SLCJ-L) directions, 135° and 90° COD tests, and four skills (acceleration step, deceleration step, sidestep, and crossover step) with an flywheel resistance device. The results showed significant differences between the higher performing and lower performing limbs across all tasks (p < 0.05). The mean asymmetry index values ranged from 1.26% (COD 135°) to 11.75% (SLC-V). Inter-limb asymmetries were greatest during the flywheel resistance skills. Spearman’s correlations (ρ) for all tests were only significant for inter-limb asymmetries during the sidestep test and reduced performance in SLCJ-L (ρ = −0.61; p = 0.046) and all COD deficits (ρ range = −0.72 to −0.81). The findings of the present study showed that inter-limb asymmetries are task-specific in female youth basketball players and suggest that the use of flywheel devices can be included in the battery of tests to detect inter-limb asymmetry.
... Across the existing literature, interlimb asymmetry is conceptualized as the difference in performance or function of one limb with respect to the other (6). In a recent paper by Dos'Santos et al. the authors highlighted that interlimb asymmetries are often categorized into one of the following: "anatomical or morphological asymmetries; flexibility asymmetries; strength asymmetries; strategy asymmetries; as well as skill or outcome asymmetries" (14). ...
... Computations for PV, and AV were calculated based on proprietary algorithms, while peak power (PP), and average power (AP) were manually calculated through the following calculation: "(load (kg) x velocity (m/s)) x 9.81". Interlimb asymmetry was calculated using the following calculation: "(Strong Limb -Weak Limb) / (Strong Limb) x 100", as suggested by Bishop et al. (6). ...
Article
Full-text available
International Journal of Exercise Science 15(6): 473-487, 2022. Over the last few years, researchers and sport scientists have expressed an increased interest in the effects of interlimb asymmetry on aspects of sport performance such as jumping, sprinting, and changing direction. This study aimed to evaluate the diagnostic utility of three different means of classifying asymmetry to highlight if a 6-week resistance training intervention can meaningfully reduce levels of asymmetry, and to determine the relation between asymmetry reduction and improvements in change of direction (CoD) performance, if any. Eighteen, division-two collegiate American football skill position players completed all pre-and post-intervention procedures. These procedures involved the completion of the Bulgarian Split Squat (BSS) exercise from which asymmetries in relative average power (Rel.AP), and relative peak power (Rel.PP) were derived. Additionally, participants completed three repetitions within the 505 and L-drill tests to quantify CoD performance. Results from our study show that participants classified as asymmetrical, exhibiting observed asymmetry in Rel.PP scores larger than the sample mean plus one standard deviation, had the greatest likelihood of reducing asymmetry (OR = 6.99, 95% CI: 1.4, 12.5) and improving L-drill performance (OR = 1.33, 95% CI:-2.1, 4.8). Further, our training intervention meaningfully reduced Rel.AP asymmetry (p = 0.027, Cohen's d = 0.73). At the group level, these reductions in asymmetry were accompanied by improvements in L-drill performance that were larger than the sample smallest worthwhile change (SWC). At the individual level, however, change scores in asymmetry and change scores in CoD performance only showed small, non-significant correlations.
... The following formula was used to identify the percentage of asymmetry between the lower limbs. In both formulas used, the results of the percent difference between the limbs were presented [25]. ...
Article
Full-text available
Introduction: Although soccer matches require players to perform repetitive power-related abilities, the impact of lower-body strength and power asymmetry on sprint and change of direction (COD) performance receives little attention. Therefore, this study aimed to establish the relationship between lower limb power, sprint, and change of direction (COD) performance. In addition, the relationship between lower limb power asymmetry and the above mentioned running tests was determined. Material and Methods: Twenty-four male soccer players from First Polish League (age = 24.8 ±8.2 years, body mass = 77.4 ±16.9kg, body height=179.5 ±14.5cm, soccer training experience = 10 ± 1.5years) took part in the study. To examine the relationship between linear sprint, lower limb muscle power, and COD performance (time and deficit), the following tests were performed: 5-and 20-m linear sprint, leg press exercise, and two 20-m COD sprints (“COD90” and “L” test). Result: Pearson correlation coefficients didn’t show any statistically significant relationship between lower limb power and linear sprint speed as well as COD performance. The results indicate that the considered variables are independent physical characteristics. Conclusion: Relative lower limb-power output and low level of mean inter-limb asymmetry in power output does not affect 5- and 20-m linear sprint time and COD performance with 90° turn.
... Comparison of unilateral neuromuscular performance is an important assessment that may provide insights into performance, prevention, rehabilitation and return to sport programmes for a wide range of athletes 7 . Multiple methods to assess asymmetry of the lower limb have been employed using various pieces of hardware and increasingly complex formulae 8 . Recently smartphone applications have been developed that can test unilateral reactive jump performance and give an asymmetry index and seem well correlated with previously considered gold standards 9,10 . ...
Poster
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Purpose: There are suggested positives and negatives to between-limb asymmetry in sports. Within professional freestyle snowboarding, proficiency in riding with either limb forward (regular or switch) is vital for a successful performance. Although not commonly mastered in amateur snowboarding, a performance including riding switch stance can dramatically increase competitive scoring. Methods: Off and on-slope jumping performance data was collected. Ten amateur snowboarders performed unilateral drop-jumps, filmed via a smartphone application (MyJump2), calculating jump performance and asymmetry of contact and flight time between limbs. A week later, performance of on-slope (Indoor Snow Centre) jumps in two stance positions (regular and switch) was recorded, also giving an asymmetry value as the difference in distance achieved between stance positions. Off and on-slope scores and asymmetries were analysed apart for differences (paired t-tests) and then off and on-slope asymmetry values were correlated (Pearson's r). Results: Off-snow ground contact times were significantly shorter and flight times significantly longer in the dominant than non-dominant leg. On-snow jump distance was significantly greater in regular stance than in switch stance. There was a strong positive correlation (r = 0.679) between off-snow contact time asymmetry and on-snow distance asymmetry. There was a strong positive correlation (r = 0.759) between regular and switch stance on-snow jump distance. Conclusions: Not withstanding the technical skill element of riding and jumping on snowboards in both regular and switch stance, it appears that reducing asymmetry is beneficial for snowboard jumping performance and there appears a relationship between off and on-snow jump performance. Further more, off-snow interventions for improved jumping performance that aim to reduce asymmetry may have a positive effect on snow based jumping performance in both stance positions.
... This approach is more objective compared to asking for each participant's preferred limb during the execution of functional performance tasks. 3,26 The magnitude of upper limb functional asymmetry ranged from 8.6-13.6% in both groups, again pointing to the presence of significant asymmetries in both groups, regardless of sex. The magnitude of handgrip strength asymmetry was found to be significantly higher in the tennis players compared to the controls (13.6% versus 8.6%, respectively), which can also be attributed to the (mostly) unilateral nature of tennis as the preferred upper limb is typically used more when executing the different tennis strokes. ...
Article
Besides examining upper and lower limb morphological and functional asymmetry magnitudes, this study examined the relationship between lean mass and functional asymmetry in terms of magnitude and direction in 41 youth tennis players versus 41 controls. Asymmetry magnitude was determined based on anthropometric measurements (circumferences, widths), bioelectrical impedance analysis (lean mass) and a test battery (handgrip strength, seated medicine ball throw, plate tapping, single leg countermovement jump, single leg forward hop test, 6 m single leg hop test, 505 change of direction). ANOVAs compared the dominant (overall highest/best value) against the non-dominant (highest/best value of opposing limb) result. Linear regressions explored the relationship between lean mass and functional asymmetry magnitudes. Kappa coefficients examined consistency in asymmetry direction between the limb displaying the highest lean mass value and the limb performing dominantly across tests. Significant asymmetry magnitudes (p<0.05) were found for all upper and lower limb morphological and functional outcome measures. No significant relationship was apparent between lean mass and functional asymmetry magnitude (r-value range=-0.283-0.262). Despite finding (almost) perfect consistency in asymmetry direction (k-value range=0.84-1.00) for the upper limb, poor to slight consistency (k-value range=-0.03-0.15) was found for the lower limb. Therefore, lean mass and functional asymmetry should be examined independently.
Article
An increased understanding of rotational strength as a potential prognostic factor for injury in contact and collision athletes may be important in planning return to sport. The aim of this study was to (1) determine the test–retest reliability of clinically relevant, angle-specific rotational and peak torque measurements in a cohort of uninjured collision and contact athletes; (2) develop a normal descriptive profile of angle-specific rotational torque measurements in the same cohort; and (3) examine the effects of direction and joint angle on shoulder rotational strength interlimb asymmetries. Twenty-three collision and contact athletes were recruited for the interday reliability substudy and 47 athletes were recruited for the remaining substudies. We used intraclass correlation coefficients with 95% confidence intervals to quantify interday reliability of all variables. We used a 2-way repeated-measures analysis of variance to analyze differences in absolute interlimb asymmetries. Interday reliability for the isokinetic strength variables was good to excellent (0.78–0.90) on the dominant side and moderate to good (0.63–0.86) on the nondominant side. Maximum angle-specific torque (as well as peak torque) can be measured reliably in internally and externally rotated positions. A normal profile of clinically relevant, angle-specific shoulder rotational torque measurements for collision and contact athletes has been established which provides a reference when assessing shoulder strength in this population.
Article
The aim of this study was to evaluate interlimb symmetry in quadriceps and hamstring peak torque of elite soccer players at 3 months (stage 1) and 6 months (stage 2) after anterior cruciate ligament (ACL) reconstruction. Eight male professional soccer players competing at the highest level across different European countries, who had undergone ACL reconstruction, participated in this study. All patients underwent a supervised physiotherapy program after surgery. Data analyses included the use of separate two-way repeated measures ANOVA-s and effect sizes. While knee extensor and flexor strength of the non-injured limb was found to be relatively unaltered (g= -0.10 to 0.00) between stage 1 and stage 2, comparisons across time points revealed moderate improvements in quadriceps peak torque (p=0.01, g=0.52), hamstring peak torque (p=0.07, g=0.51), and hamstring/quadriceps (H/Q) ratio (p=0.03, g= -0.68) of the injured leg, as well as small-large improvements in the quadriceps (p=0.004, g=1.24) and hamstring limb symmetry index (LSI) (p=0.056, g=0.41). A time-dependent moderate-large asymmetry observed at stage 1 between the injured and non-injured leg in quadriceps peak torque (p< 0.001, g= -1.83), hamstring peak torque (p=0.157, g= -0.67), and the H/Q ratio (p=0.06, g=1.01), as well as between the hamstring and quadriceps LSI (p=0.03, g= -0.74) was eliminated at stage 2 (g= -0.31 to 0.42). Our findings indicate the importance of supervised and comprehensive therapy, as well as strength screening to assist in recovery aimed at optimizing identified strength deficits following ACL reconstruction.
Article
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Whilst the measurement and quantification of vertical leg stiffness (Kvert) asymmetry is of important practical relevance to athletic performance, literature investigating bilateral asymmetry in Kvert is limited. Moreover, how the type of task used to assess Kvert may affect the expression of asymmetry has not been properly determined. Twelve healthy males performed three types of performance tasks on a dual force plate system to determine Kvert asymmetries; the tasks were (a) bilateral hopping, (b) bilateral drop jumping and (c) unilateral drop jumping. Across all the three methods, Kvert was significantly different between compliant and stiff limbs (P < 0.001) with a significant interaction effect between limb and method (P = 0.005). Differences in Kvert between compliant and stiff limbs were -5.3% (P < 0.001), -21.8% (P = 0.007) and -15.1% (P < 0.001) for the bilateral hopping, bilateral drop jumping and unilateral drop jumping methods, respectively. All the three methods were able to detect significant differences between compliant and stiff limbs, and could be used as a diagnostic tool to assess Kvert asymmetry. Drop jumping tasks detected larger Kvert asymmetries than hopping, suggesting that asymmetries may be expressed to a greater extent in acyclic, maximal performance tasks.
Article
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Background: While measures of asymmetry may provide a means of identifying individuals predisposed to injury, normative asymmetry values for challenging sport specific movements in elite athletes are currently lacking in the literature. In addition, previous studies have typically investigated symmetry using discrete point analyses alone. This study examined biomechanical symmetry in elite rugby union players using both discrete point and continuous data analysis techniques. Methods: Twenty elite injury free international rugby union players (mean ± SD: age 20.4 ± 1.0 years; height 1.86 ± 0.08 m; mass 98.4 ± 9.9 kg) underwent biomechanical assessment. A single leg drop landing, a single leg hurdle hop, and a running cut were analysed. Peak joint angles and moments were examined in the discrete point analysis while analysis of characterising phases (ACP) techniques were used to examine the continuous data. Dominant side was compared to non-dominant side using dependent t-tests for normally distributed data or Wilcoxon signed-rank test for non-normally distributed data. The significance level was set at α = 0.05. Results: The majority of variables were found to be symmetrical with a total of 57/60 variables displaying symmetry in the discrete point analysis and 55/60 in the ACP. The five variables that were found to be asymmetrical were hip abductor moment in the drop landing (p = 0.02), pelvis lift/drop in the drop landing (p = 0.04) and hurdle hop (p = 0.02), ankle internal rotation moment in the cut (p = 0.04) and ankle dorsiflexion angle also in the cut (p = 0.01). The ACP identified two additional asymmetries not identified in the discrete point analysis. Conclusions: Elite injury free rugby union players tended to exhibit bi-lateral symmetry across a range of biomechanical variables in a drop landing, hurdle hop and cut. This study provides useful normative values for inter-limb symmetry in these movement tests. When examining symmetry it is recommended to incorporate continuous data analysis techniques rather than a discrete point analysis alone; a discrete point analysis was unable to detect two of the five asymmetries identified.
Article
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The assessment of vertical leg stiffness is an important consideration given its relationship to performance. Vertical stiffness is most commonly assessed during a bilateral hopping task. The current study sought to determine the inter-session reliability, quantified by the coefficient of variation, of vertical stiffness during bilateral hopping when assessed for the left and right limbs independently, this had not been previously investigated. On four separate occasions, ten healthy males performed 30 unshod bilateral hops on a dual force plate system with data recorded independently for the left and right limbs. Vertical stiffness was calculated as the ratio of peak ground reaction force to the peak negative displacement of the centre of mass during each hop and was averaged over the 6-10th hops. For vertical stiffness, average coefficients of variation of 15.3% and 14.3% were observed for the left and right limbs respectively. An average coefficient of variation of 14.7% was observed for bilateral vertical stiffness. The current study reports that calculations of unilateral vertical stiffness demonstrate reliability comparable to bilateral calculations. Determining unilateral vertical stiffness values and relative discrepancies may allow the coach to build a more complete stiffness profile of an individual athlete and better inform the training process.
Article
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Bilateral asymmetries and muscle imbalances are associated with increased risk for lower limb injuries and still seem to imply in athletes performance. This study aimed to analyze bilateral asymmetry of soccer players in age category below 20 years old (peak torque and conventional and functional reason in extensor/flexors of knee and inverter/ eversion of ankle) and to compare these variables between defending, midfield and attacker players. The study included 22 athletes in age category below 20, which underwent a five maximal isokinetic testing with repetitions at 180°/s for knee and 120°/s for ankle, both concentric and eccentric actions. T test for dependent data was used to compare values of torque between dominant and non-dominant limbs and one-way ANOVA was used to compare neuromuscular variables between players of different positions, both at p <0.05. No significant differences were observed in any neuromuscular variable (peak torque and functional and conventional ratio) between dominant and non-dominant sides (p> 0.05). It was found that defensive players had eccentric torque values of extensors knee higher than midfield players (p <0.05). Defensive players exhibit greater eccentric torque of knee extensor muscles compared to midfield players. It can be concluded that the analyzed soccer players did not present bilateral asymmetries in flexor/extensor knee muscles neither in inverter/eversion ankle muscles. Key words: Asymmetry index; Injury; Muscle imbalance; Soccer.
Article
Functional testing is used to assess anterior cruciate ligament (ACL) reconstruction rehabilitation, with the goal of symmetric ability. The pattern of change in the uninvolved limb's function during rehabilitation is not established. (1) Involved and uninvolved limb ability increases during rehabilitation, but the uninvolved limb ability increases to a lesser degree. (2) Hop tests will show larger initial asymmetry and will improve the most with rehabilitation. Cohort study; Level of evidence, 3. This was a retrospective case series of 122 patients who underwent ACL reconstruction at our ambulatory surgery center and received multiple postoperative Standard Functional Tests (SFTs) between October 2009 and October 2013. Ten of the 12 individual tests within the SFT battery were analyzed. The patients' earliest and latest SFTs were compared for changes in Limb Symmetry Index (LSI) and absolute function in each limb. We also analyzed the subgroup with SFTs (n = 38) at both 4 and 6 months postoperatively. In all patients with multiple SFTs, involved limb performance increased in all tests except eyes-closed stork. Uninvolved limb performance increased in 4 SFT component tests and decreased in none. LSI significantly improved in 6 tests, all of which also showed involved limb improvement that was significant. Of these 6 tests, 5 showed initial LSI below 90%: single-leg squat, retro step-up, single-leg hop, crossover triple hop, and timed hop. Retro step-up and single-leg hop showed LSI improvements greater than 10 percentage points. In patients with 4- and 6-month data, involved limb performance increased in all tests except single-leg triple hop. Uninvolved limb performance increased in 5 SFT component tests and decreased in none. LSI significantly improved in 4 tests, all of which had initial LSI below 90%, and showed involved limb improvement that was significant. Retro step-up, single-leg hop, and crossover triple hop showed LSI improvements greater than 10 percentage points. During ACL reconstruction rehabilitation, LSI improvements indicated absolute increases in involved limb ability and were not attributable to uninvolved limb deterioration. The single-leg squat, retro step-up, single-leg hop, crossover triple hop, and timed hop are suggested as highly useful tests, since all showed initial LSI below 90%, with significant LSI improvement after rehabilitation. © 2015 The Author(s).
Article
STATISTICAL ANALYSIS IS CRUCIAL TO THE ROLE OF STRENGTH AND CONDITIONING, AND COACHES SHOULD BE ABLE TO IDENTIFY WHETHER THEIR DATA ARE RELIABLE AND OBJECTIVELY DETERMINE DIFFERENCES AND RELATIONSHIPS. THESE ANALYTICAL SKILLS ARE CENTRAL TO OUR ABILITY OF UNCOVERING TRENDS AND ASSOCIATIONS, MAKING PREDICTIONS AND ASSESSING THE EFFICACY OF TRAINING PROGRAMS. THIS ARTICLE REVIEWS STATISTICAL TESTS AVAILABLE THROUGH MICROSOFT EXCEL, COVERING RELIABILITY (THROUGH THE COEFFICIENT OF VARIATION), THE SMALLEST WORTHWHILE CHANGE (I.E., THE FIRST MEANINGFUL DIFFERENCE IN SCORES), EFFECT SIZES (I.E., THE MAGNITUDE OF CHANGE BETWEEN PERFORMANCE SCORES), AND RELATIONSHIPS (I.E., CORRELATIONS).
Article
The present study aimed to clarify the asymmetry between the dominant (DL) and non-dominant takeoff legs (NDL) in terms of lower limb behavior during running single leg jumps (RSJ) in collegiate male basketball players in relation to that of the jump height. Twenty-seven players performed maximal RSJ with a 6 m approach. Three-dimensional kinematics data during RSJ was collected using a 12 Raptor camera infrared motion analysis system (MAC 3D system) at a sampling frequency of 500 Hz. The symmetry index in the jump heights and the kinematics variables were calculated as {2 × (DL - NDL) / (DL + NDL)} × 100. The run-up velocity was similar between the two legs, but the jump height was significantly higher in the DL than in the NDL. During the takeoff phase, the joint angles of the ankle and knee were significantly larger in the DL than the NDL. In addition, the contact time for the DL was significantly shorter than that for the NDL. The symmetry index of the kinematics for the ankle joint was positively correlated with that of jump height, but that for the knee joint was not. The current results indicate that, for collegiate basketball players, the asymmetry in the height of a RSJ can be attributed to that in the joint kinematics of the ankle during the takeoff phase, which may be associated with the ability to effectively transmit run-up velocity to jump height. Key pointsAsymmetry of height during running single leg jump between two legs is due to the behavior of the ankle joint (i.e. stiffer the ankle joint and explosive bounding).The dominant leg can transmit run-up velocity into the vertical velocity at takeoff phase to jump high compared with the non-dominant leg.Basketball players who have a greater asymmetry of the RSJ at the collegiate level could be assessed as non-regulars judging by the magnitude of asymmetry.