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Lower Body Symmetry and Running Performance in Elite
Jamaican Track and Field Athletes
Robert Trivers
1
*, Bernhard Fink
2
, Mark Russell
3
, Kristofor McCarty
4
, Bruce James
5
, Brian G. Palestis
6
1Graduate Program in Ecology and Evolution, Rutgers University, New Brunswick, New Jersey, United States of America, 2Courant Research Centre, Evolution of Social
Behavior & Institute of Psychology, University of Go
¨ttingen, Go
¨ttingen, Germany, 3Faculty of Health and Life Sciences, Northumbria University, Newcastle-upon-Tyne,
United Kingdom, 4Department of Psychology, Faculty of Health and Life Sciences, Northumbria University, Newcastle-upon-Tyne, United Kingdom, 5MVP Track and Field
Club, University of Technology, Kingston, Jamaica, 6Department of Biological Sciences, Wagner College, Staten Island, New York, United States of America
Abstract
In a study of degree of lower body symmetry in 73 elite Jamaican track and field athletes we show that both their knees and
ankles (but not their feet) are–on average–significantly more symmetrical than those of 116 similarly aged controls from the
rural Jamaican countryside. Within the elite athletes, events ranged from the 100 to the 800 m, and knee and ankle
asymmetry was lower for those running the 100 m dashes than those running the longer events with turns. Nevertheless,
across all events those with more symmetrical knees and ankles (but not feet) had better results compared to international
standards. Regression models considering lower body symmetry combined with gender, age and weight explain 27 to 28%
of the variation in performance among athletes, with symmetry related to about 5% of this variation. Within 100 m
sprinters, the results suggest that those with more symmetrical knees and ankles ran faster. Altogether, our work confirms
earlier findings that knee and probably ankle symmetry are positively associated with sprinting performance, while
extending these findings to elite athletes.
Citation: Trivers R, Fink B, Russell M, McCarty K, James B, et al. (2014) Lower Body Symmetry and Running Performance in Elite Jamaican Track and Field
Athletes. PLoS ONE 9(11): e113106. doi:10.1371/journal.pone.0113106
Editor: Patrizia d’Ettorre, University of Paris 13, France
Received July 2, 2014; Accepted October 15, 2014; Published November 17, 2014
Copyright: ß2014 Trivers et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. Data have been deposited to Dryad (http://dx.
doi.org/10.5061/dryad.s3630).
Funding: The authors thank the Enhanced Education Foundation, the Ann and Gordon Getty Foundation, the Biosocial Research Foundation, the Center for
Human Evolutionary Studies (CHES), and the German Science Foundation (DFG) for financial support. The funders had no role in study design, data collection and
analysis, decision to publish, or preparation of the manuscript.
Competing Interests: Bernhard Fink serves as an academic editor for PLOS ONE. This does not alter the authors’ adherence to PLOS ONE editorial policies and
criteria. With regard to the affiliation of coauthor Bruce James: Mr. James has provided the authors with access to the sample of elite athletes of this present study;
he has also been involved in the on-site measurement logistics and activities in Kingston. Aside from this, Mr. James had neither a financial interest nor an
influence on the outcome of the study results. This does not alter the authors’ adherence to PLOS ONE editorial policies and criteria.
* Email: trivers@rci.rutgers.edu
Introduction
Trivers et al. [1] showed that Jamaican eight year olds of both
sexes with more symmetrical knees were better sprinters 14 years
later in both the 100 and the 200 m dashes, while symmetry of the
upper body and feet did not predict sprinting speed, and ankle
symmetry sometimes seemed to have a minor positive effect on
sprinting speed. There are two separate reasons why we might
expect symmetry of lower body traits to be positively associated
with sprinting speed. Symmetry is inherently more efficient in
races–it is less physically demanding and thus saves energy. This is
presumably why the lower body asymmetry of Jamaican children
8.2 years of age is 1/3
rd
that of upper body asymmetry [2].
Walking and running are inherently symmetrical and should favor
symmetrical traits associated with them while upper body
movements may or may not be symmetrical (vide, laterality) [3,4].
On the other hand, it has been known since the 1950’s from
experimental work on Drosophila that stress during early
development is associated with greater adult bodily asymmetry,
as is genetic inability to deal with the stress (e.g., inbred vs.
outbred). This led to the notion that fluctuating asymmetry (FA) –
deviations from bilateral symmetry in paired traits, randomly
distributed to the left and right side – is a measure of
developmental instability, i.e., the inability of an organism
genetically to buffer the system against stressors to achieve the
optimal state, namely symmetry itself [5]. The key is that if a
population shows true FA then it can be presumed to be
attempting to be symmetrical, so that failure to do so is a measure
of failure to reach–in the face of developmental perturbations–the
phenotype that the genotype is aiming for. Once it was discovered
that females in a variety of birds, insects and mammals preferred
symmetrical males as mating partners, even in species lacking male
parental investment, it became obvious that body symmetry must
be positively associated with genetic quality–a resistance from
disease, for example [6], and many other advantageous traits [7].
To test for associations between symmetry and athletic
performance, we compared lower body symmetry (knees, ankles
and feet) in a control sample of Jamaicans measured in the
countryside, carefully matched to a sample of elite Jamaican
athletes measured in Kingston (all members of the MVP Track
and Field Association). Among the elite athletes we also obtained
performance–best times in preferred events against world records–
to see if variation in peak sprinting times was in part predicted by
variation in lower body symmetry.
PLOS ONE | www.plosone.org 1 November 2014 | Volume 9 | Issue 11 | e113106
In this paper we show that elite athletes have markedly more
symmetrical knees than countryside controls and also more
symmetrical ankles, while symmetry of feet does not differ between
the two. We further demonstrate that within elite sprinters,
performance shows striking and consistent positive associations
with both knee and ankle symmetry. To wit, taking all athletes
together, knee symmetry predicts sprinting ability while ankle
symmetry almost does so. By adding covariates, such as weight and
age, knee and ankle symmetry remain as marginally significant
predictors of athletic success at the highest level of elite
performance. Considering only the 100 m sprinters (n = 32) we
find positive correlations between degree of knee and ankle
symmetry and world performance. It also seems noteworthy that
overall symmetry decreases among those who run 200 m, 400 m
or 800 m races, as if adapted to or caused by frequent left-hand
turns.
Methods
Subjects
We recruited two groups of subjects: elite Jamaican track and
field athletes and controls from the Jamaican countryside. The
elite athletes were all members of the MVP Track and Field Club
working out of University of Technology in Kingston. We were
able to get a nearly complete sample of club membership (73 of
77). There are exclusive criteria for being members of MVP and it
is highly sought after by up and coming Jamaican athletes.
International Association of Athletics Federations (IAAF) scores
allow comparisons across disciplines and genders [8] (www.iaaf.
org) and we used these scores, which we calculated based on
personal bests, as our measure of performance. Approximately
90% of MVP club members have IAAF scores above 1000, and 6
of our subjects have remarkably high scores ($1200). Although
their training all included sprinting, the athletes’ best events
varied, and in addition to comparing athletes and controls, we also
compared symmetry of athletes whose specialties differed.
Control subjects consisted of individuals recruited in the
countryside through word of mouth by someone who knew the
community very well and had worked with the Jamaican
Symmetry Project [2] since its inception in 1996. This person
was given an exact list of the ages and sexes of the elite athletes we
would be measuring in Kingston, so she could recruit a matching
sample, which she did exactly. We then invited additional subjects
who were within the age range of the elite athletes to appear and
be measured, except that we discouraged all overweight individ-
uals (which were overwhelmingly women) since we doubted there
were many overweight elite athletes. The final number of control
subjects was 116.
Elite athletes and controls were of very similar age (athletes:
mean+/2SD = 23.0+/23.2; controls 23.0+/23.6; t
187
= 0.14,
p = 0.89). There is also no difference in variance in age between
groups (Levene’s test, F = 1.68, p = 0.20) and the ranges are as
follows: elite 17.13–31.95; control 17.21–32.46.
Measurement of traits
Before traveling to Jamaica the three measurers met, and each
measurer was exclusively allocated one trait to eliminate between-
measurer effects. There were two sessions, each of approximately 6
hours, in which the measurement points for knees, ankles and feet
were agreed upon and preliminary repeatability for each trait was
established. Measurement points were the same as adopted in the
Jamaican Symmetry Project in 1996 [2] and thus match the
landmarks used in Trivers et al. [1].
When conducting the study in Jamaica, we measured the traits
twice per side for each individual (second foot measurements
missing for one subject). Repeated measurement is standard in FA
studies, because the differences between sides are often so small
that they can be similar in magnitude to measurement error [9–
11]. Only by measuring each side at least twice can one
demonstrate that the differences between sides reflect actual
asymmetry, rather than measurement error. The calculated
average of the two measurements were used in the subsequent
statistical analysis.
To preserve anonymity each participant received a unique ID at
arrival, printed on A6 cards, and only this number was used to
assign his/her measurements. Measurements of the three lower
body traits were all performed using a digital Vernier caliper
(Preisser products, Germany) to an accuracy of 0.01 mm. To
eliminate potential measurement biases, the calipers were closed
after each measurement. In addition to the three lower body traits,
weight and height were measured and age was self-reported.
Collecting all measurement took approximately 10 minutes per
participant and there was a time span of some 3–5 minutes
between first and second measurements of a trait, in which
participants completed measurements at another station before
they returned for the second measurement. Each measurement
was called out to an assistant sitting next to the investigator to
ensure that the investigator could not memorize them.
The size of the left and right knee of each participant was
measured as defined by the largest breadth, measured between the
medial and lateral epicondyles of the femur. The investigator
measuring ankles first located the widest point of the ankle by hand
before putting the caliper in place. For both knee and ankle
measurements, participants were seated on a chair with legs bent
by 90uand measurements were taken by an investigator sitting in
front of the participant. Somatometric landmarks were palpated
and measurements were taken with constant pressure of the caliper
to minimize soft tissue related measurement error. Foot length was
measured bilaterally using standardized A3 graphical paper
(resolution of 1 mm) that was then measured with calipers. In a
seated position, participants were instructed to place both feet on
to the paper in a manner which aligned the pternion to the head of
the 2nd metatarsal axes of each foot in parallel. Using a leveling
device, markings were placed at the pternion and at the tip of toe
one of each foot. To ensure consistency of measurement, markings
were placed at the tip of toe one irrespective of whether toes two
through five would have elicited a greater foot length. The
perpendicular distance between two parallel lines extrapolated
from the original foot markings was deemed foot length.
Statistical analysis
Most analyses were performed using IBM SPSS Statistics 21. The
presence of fluctuating and directional asymmetry (FA and DA)
were assessed using the Excel template at www.biology.ualberta.ca/
palmer/asym/FA/FA-Refs.htm#tools. With this template, the
presence of significant FA (FA .measurement error) is demon-
strated by a significant F-test for a sides X individuals interaction in
a mixed model ANOVA [9,10]. DA is indicated by a significant
effect of sides in the ANOVA model.
Significant DA was present in feet and ankles (see Measure-
ments in the main text). To ensure that statistical tests are
comparing FA and are not biased by directional differences
between sides, we used the index of FA developed by Graham
et al. [11]. This index is based on unrotated factors extracted from
the covariance matrix of a principal component analysis of the
mean right side measurements on a trait and the mean left side
measurements. This first factor represents the covariance between
Symmetry in Elite Jamaican Athletes
PLOS ONE | www.plosone.org 2 November 2014 | Volume 9 | Issue 11 | e113106
sides, plus half the FA and half the remaining measurement error.
The second factor represents half the FA and half the remaining
measurement error. This second factor is therefore an index of FA
and does not include DA, which would be extracted with the
covariance between sides. When analyzing overall asymmetry,
including DA, we use relative asymmetry (absolute asymmetry in a
trait divided by trait size).
Unsigned FA (absolute value of right – left) has an asymmetrical
frequency distribution with only half of a bell curve. However, FA
should not then be transformed to achieve normality, because F-
tests are robust and transformation may change the underlying
relationships between FA and other variables [10,12]. Compar-
isons of FA are comparisons of variance in a trait, and
comparisons of the means of two half-normal distributions gives
an unbiased estimate of differences in variance [9,10]. Parametric
correlation and regression analyses are also robust in this case [12].
To avoid inflating Type I error by conducting multiple tests,
multivariate analyses were used whenever appropriate. When the
dependent variables were FA in individual traits, the three traits
were tested simultaneously using multivariate GLM in SPSS
(MANOVA, MANCOVA). When testing dependent variable
composite FA (sum of the FA index for the three traits) we used
univariate GLMs (ANOVA, ANCOVA). When the FA values
were the independent variables and athletic performance (indexed
by IAAF scores) the dependent variable, we used multiple
regression.
Significance tests were conducted with an alpha level of 0.05,
and, whenever appropriate, effect sizes are given in addition to p-
values. Tests are two-tailed except when testing for relationships
between FA and racing performance. In these situations we use a
directed test, a compromise between one and two-tailed testing for
strongly directional hypotheses [13,14]. Our previous work [1]
showed a positive relationship between symmetry (low FA) and
sprinting and there is no reason to expect that greater symmetry
would result in poorer performance, therefore we have a strong
directional hypothesis. Our other comparisons are not as obviously
directional: effects of weight, age, and gender on FA and on
performance and effects of athletic training on FA.
The dataset is available in the Dryad repository (http://doi.org/
10.5061/dryad.s3630).
Ethical statement
This research was approved by the Institutional Review Board
of Rutgers University, protocol #14–425 M. All participants were
Figure 1. Boxplots for the three traits and their sum. FA is corrected for directional asymmetry using Graham et al.’s index (see Methods). Elite
athletes (n = 73) are represented by open bars and controls (n = 116) by bars filled with diagonals. Circles represent outliers, with stars indicating
extreme outliers; color of circles and stars corresponds to coloring in bars. Controls have significantly higher knee, ankle and composite FA than the
athletes (see Tables 1–3).
doi:10.1371/journal.pone.0113106.g001
Symmetry in Elite Jamaican Athletes
PLOS ONE | www.plosone.org 3 November 2014 | Volume 9 | Issue 11 | e113106
informed on the purpose of the study and gave written consent.
Permission of legal guardians was also obtained for subjects below
18 years of age.
Results
Measurements
Mean values (+/2SD) for the three traits are as follows (all
n = 189): right knee 96.80 mm+/27.63; left knee 96.66+/27.94;
right ankle 67.99+/25.40; left ankle 68.70+/25.48; right foot
259.89+/217.23; left foot 261.03+/217.49. A Mixed Model
Sides X Individuals ANOVA (see Methods) demonstrates signif-
icant FA in all 3 traits (FA .measurement error: knees
F
188,378
= 1.96; ankles F
188,378
= 2.91; feet F
188.376
= 5.55; all p,
0.0001) and significant directional asymmetry (DA) in ankles
(F
1,188
= 34.76, p,0.0001) and feet (F
1,188
= 23.00, p,0.0001) but
not knees (F
1,188
= 1.47, p = 0.23). The left foot and ankle tended
to be larger than the right: 64.0% of subjects had larger left ankles
and 61.9% had larger left feet, with little variation among groups.
The significant p-values are so low that they are still at the
p,0.0001 level even with any correction for multiple tests.
Because of the presence of DA, we use FA values corrected for DA
(see Methods).
Athletes vs. controls
Mean values of the FA index (corrected for DA) for athletes and
controls are presented in Figure 1. The FA index was compared
between elite athletes and controls in MANOVAs with dependent
variables knee, ankle and foot asymmetry, and group (elite vs.
control) and gender as the factors. There are significant differences
between athletes and controls in knee and ankle asymmetry, but
not in foot asymmetry (Table 1). There were no significant sex
differences, but a significant gender x group interaction for knees
because female controls had particularly high mean knee FA
Table 1. Statistical comparisons of FA index between athletes and controls.
Treatment Pillai’s Trace F
3,183
P
Athlete vs. Control 0.083 5.55 0.001*
Gender 0.013 0.83 0.48
Gender X A v. C 0.041 2.59 0.055
Factor Trait F
1,185
P Partial eta
2
Athlete vs. Control Knee 10.37 0.002* 0.053
Athlete vs. Control Ankle 4.55 0.034* 0.024
Athlete vs. Control Foot 0.62 0.43 0.003
Gender Knee 2.24 0.13 0.012
Gender Ankle 0.26 0.61 0.001
Gender Foot 0.04 0.84 ,0
Gender X A. v. C. Knee 4.60 0.033* 0.024
Gender X A. v. C. Ankle 0.001 0.97 ,0
Gender X A. v. C. Foot 3.13 0.079 0.017
Multivariate tests compare the three traits simultaneously (knee, ankle, foot). Statistically significant relationships (two-tailed tests, alpha = 0.05) are indicated with
asterisks.
doi:10.1371/journal.pone.0113106.t001
Table 2. Statistical comparisons of composite FA index (knee, ankle, and foot FA combined) between athletes and controls.
Factor F
1,185
P Partial eta
2
Athlete vs. Control 13.24 ,0.0001* 0.067
Gender 0.54 0.46 0.003
Gender X A. v. C. 0.07 0.80 ,0
Factor F
1,183
P Partial eta
2
Athlete vs. Control 12.82 ,0.001* 0.065
Gender 1.63 0.20 0.009
Gender X A. v. C. 0.002 0.96 ,0
Age 0.33 0.56 0.002
Weight 1.99 0.16 0.011
Results are shown first with no covariates (F
3,185
= 4.86, p = 0.003, adjusted r
2
= 0.058) and then with covariates age and weight added (F
5,183
= 3.46, p = 0.005, adjusted
r
2
= 0.061). Statistically significant relationships (two-tailed tests, alpha = 0.05) are indicated with asterisks.
doi:10.1371/journal.pone.0113106.t002
Symmetry in Elite Jamaican Athletes
PLOS ONE | www.plosone.org 4 November 2014 | Volume 9 | Issue 11 | e113106
(mean+/2SD = 1.04+/20.82, n = 56; compare to Figure 1).
Using composite asymmetry (sum of knee, foot, ankle) rather than
individual traits again demonstrates significant differences between
athletes and controls and no significant effect of gender, but also
no significant gender x group interactions (Table 2).
Including weight and age as covariates does not change the key
results Again significant differences between athletes and controls
are present for composite FA (Table 2) and separately for knees
and ankles, but not feet (Table 3). The gender x group interaction
is now significant for both knees and feet, rather than just knees,
but not when using composite FA. There is also a positive
relationship between weight and foot FA, but the overall
relationship with weight is marginal and there are no significant
relationships between age and FA (Tables 2,3).
Within-athlete comparisons
Relationships between FA and performance of the athletes,
measured by IAAF scores, were tested using multiple regression.
For FA we used the residuals of a regression between FA corrected
for DA and discipline, to control for effects of particular events on
symmetry (see below). There is a significant negative relationship
between composite FA and performance (i.e., more symmetrical
athletes perform better; Table 4). Among individual traits, a
significant relationship is present for knees, with ankles marginal
(directional p = 0.087; Table 4). There is also a significant effect of
gender. Even without considering covariates age and weight, the
regression model explains 12 to 13% of the variance in
performance (adjusted r
2
= 0.12 when using composite FA and
0.13 when using individual traits). Partial r
2
values indicate that
knee or composite FA, depending on the model, are each related
to approximately 5% of the variation in performance (Table 4).
When age and weight are added in as covariates, there is a
strong positive relationship between age and performance, and the
regression model explains 27 to 28% of the variance in
performance (adjusted r
2
= 0.27 when using composite FA and
0.28 when using individual traits; Table 5). The relationship with
composite FA remains significant and is related to 5% of the
variation in performance, but relationships with weight and with
individual traits are not significant (both knees and ankles are
marginal; Table 5). The effect of gender is no longer significant,
and likely resulted in part from a selection effect based on age:
generally the most successful athletes are those most likely to
continue competing as they age, and this may be especially true of
women. Examination of the historical records of those six males
and six females with the top ten finishes per sex (two of whom are
in our sample) reveals that the age effect is probably not only due
to selection–there is also typically a within-individual improvement
with age for several years, but then a leveling off and a decline late
in an athlete’s career, circa 28 years (www.iaaf.org/athletes).
We also conducted analyses restricted to those whose best event
is the 100 m sprint, because we predicted the relationship between
FA and performance to be particularly important for sprinting
events and our sample for sprinters, although small (n = 32), is
larger than for any other events. Here we use the index of FA
corrected for DA, but not the residuals with event, because we are
testing within one event. A regression with dependent variable
IAAF score and independent variables gender, knee, ankle, and
foot FA is not significant (F
4,27
= 1.97, p = 0.13, adjusted r
2
= 0.11)
but suggests relationships with knee and ankle FA (b=20.33,
directional p = 0.044 and b=20.33, p = 0.045, respectively), but
not foot FA (b= 0.18, p = 0.46) or gender (b= 0.10, two-tailed
p = 0.56). The overall regression model is significant when
covariates age and weight are added (F
6,25
= 2.84, p = 0.030,
adjusted r
2
= 0.26), but the apparent relationships with knee and
ankle FA are no longer significant (knees: b=20.11, directional
p = 0.34; ankles: b=20.24, p = 0.093). For foot FA, b= 0.13,
p = 0.55. Two-tailed p-values for the other variables are all greater
than 0.05, but less than 0.10. Relationships with composite FA are
not significant (directional p = 0.31 without covariates, 0.43 with
covariates), because, within sprinters, foot FA trends opposite the
predicted direction and therefore when knee and ankle FA are
combined with foot FA the relationships become weaker. When
using composite FA, significant effects of gender (b= 0.62, two-
tailed p = 0.017), age (b= 0.39, p = 0.024), and weight (b= 0.55,
p = 0.034) are all present and 25% of the variation in sprinting
performance is explained (F
4,27
= 3.56, p = 0.019, adjusted
r
2
= 0.25). IAAF scores should not show significant differences
between males and females, because they are calculated to allow
comparison of relative performance regardless of gender. The
significant relationship we find is likely a result of our sample
happening to contain particularly successful female sprinters.
In addition to testing for relationships between FA and
performance, we tested whether symmetry among athletes varied
with their primary event, because events differ in the stresses they
produce and may cause both fluctuating and directional asym-
metry. Because of small sample sizes for several events, the events
were combined into three categories: straight sprints (100 m,
n = 32), longer races with turns (200 m, 400 m, 800 m; n = 29),
and events with jumping or leaping (100 and 110 m hurdles,
400 m hurdles, long jump, high jump; n =11) [the one shot-putter
was excluded]. An ANOVA test revealed significant variation
among these categories in relative composite FA (not corrected for
DA): F
2,69
= 3.67, p = 0.031. A Tukey’s HSD post-hoc test
revealed that longer distance runners were significantly more
asymmetrical than sprinters. Means for sprinting and jumping
events were similar. In a MANOVA, there were no significant
differences among groups for the individual traits, but the trends
for knees and especially ankles match the trend for composite FA
(Fig. 2). If we use the FA index corrected for DA the patterns are
similar, but are not significant (composite FA index, F
2,69
= 2.37,
p = 0.10). However, here we specifically want to test the effects of
athletic stresses, which are often asymmetric, on overall symmetry
and therefore DA should be included. Above we were interested
instead in the relationships between developmental stability
(indexed by FA) and performance, and thus needed to factor out
DA.
Discussion
Jamaicans are the elite sprinters of the world. Why? If symmetry
of knees and ankles is a factor, why should Jamaicans be especially
symmetrical (there is no knowledge of whether they actually are)?
One possibility is heterozygosity for genes important to sprinting.
The slave trade greatly increased heterozygosity on the West
African side by mixing genes up and down the West coast of Africa
from Senegal to Nigeria [15,16]. Recently a mtDNA haplotype
has been isolated that correlates with success in African American–
but not Jamaican–sprinters [17]. Since there is a general (if often
weak) positive relationship between heterozygosity and body
symmetry [18] we are eager to do targeted studies of genomics
on areas associated with sprinting, including energy substrate
utilization, muscle fibre-type distribution and body composition
analyses (with specific reference to the shape and size of the glutei
maximi). Fast twitch (anaerobic) muscle fibres are characterized by
specific adaptations which benefit the performances of explosive
high-intensity actions such as those involved in sprinting. Notably,
West Africans appear to have a higher fast twitch muscle fibre
Symmetry in Elite Jamaican Athletes
PLOS ONE | www.plosone.org 5 November 2014 | Volume 9 | Issue 11 | e113106
content than do comparable Europeans (67.5% vs 59% in one
sample [19], as cited in [20]).
An interesting problem arises. How much is genetic quality
revealed by overall body symmetry and how much is it associated
with symmetry of particular body parts? To give a (partly)
counterintuitive example, over-all body symmetry, based on 10
measurements of race horses, is positively correlated with
performance in competitive races, but both lower body asymme-
try, especially of the knees, is a correlate and so also are features of
the head [21], as if the symmetry of the apparatus controlling the
running (brain, head, sensory organs) is as important as the parts
doing the running (themselves already selected for symmetry as
shown in the Jamaican children, see [1]). Møller and colleagues
[22] also demonstrated a link between lower-body symmetry and
locomotion (in chickens), but did not measure upper-body traits.
Manning and Pickup [23] showed for humans that degree of
nostril symmetry positively predicts running performance in
middle-distance runners, which is plausible since middle distance
Table 3. Statistical comparisons of FA index between athletes and controls, with age and weight added as covariates.
Treatment Pillai’s Trace F
3,181
P
Athlete vs. Control 0.083 5.43 0.001*
Gender 0.023 1.43 0.24
Gender X A v. C 0.046 2.94 0.035*
Age 0.021 1.29 0.28
Weight 0.036 2.23 0.087
Factor Trait F
1,185
P Partial eta
2
Athlete vs. Control Knee 10.21 0.002* 0.053
Athlete vs. Control Ankle 4.52 0.035* 0.024
Athlete vs. Control Foot 0.49 0.48 0.003
Gender Knee 2.26 0.14 0.012
Gender Ankle 0.38 0.54 0.002
Gender Foot 1.74 0.19 0.009
Gender X A. v. C. Knee 4.34 0.039* 0.023
Gender X A. v. C. Ankle 0.002 0.96 ,0
Gender X A. v. C. Foot 4.50 0.035* 0.024
Age Knee 0.13 0.72 0.001
Age Ankle 0.88 0.35 0.005
Age Foot 2.73 0.10 0.015
Weight Knee 0.04 0.84 ,0
Weight Ankle 0.05 0.82 ,0
Weight Foot 6.57 0.011* 0.035
Multivariate tests compare the three traits simultaneously (knee, ankle, foot). Statistically significant relationships (two-tailed tests, alpha = 0.05) are indicated with
asterisks.
doi:10.1371/journal.pone.0113106.t003
Table 4. Multiple regressions within athletes, testing for relationships with performance (IAAF scores).
Factor Beta Partial r
2
P
Individual Traits
Resid. Knee FA 20.22 0.05 0.040*
Resid. Ankle FA 20.17 0.03 0.087
Resid. Foot FA 20.09 0.01 0.28
Gender 0.31 0.10 0.007*
Composite FA
Resid. Composite FA 20.22 0.05 0.031*
Gender 0.33 0.11 0.004*
FA values are residuals of the FA index on the athletes’ primary events. Results are shown first for individual traits (F
4,68
= 3.38, p = 0.014, adjusted r
2
= 0.12) and then for
composite FA (F
2,70
= 6.20, p = 0.003, adjusted r
2
= 0.13). P-values for the predicted relationship between FA and performance are directional (see Methods), and
statistical significance is indicated by asterisks.
doi:10.1371/journal.pone.0113106.t004
Symmetry in Elite Jamaican Athletes
PLOS ONE | www.plosone.org 6 November 2014 | Volume 9 | Issue 11 | e113106
Table 5. Multiple regressions within athletes, testing for relationships with performance (IAAF scores) with age and weight added
as covariates.
Factor Beta Partial r
2
P
Individual Traits
Resid. Knee FA 20.16 0.03 0.084
Resid. Ankle FA 20.16 0.03 0.081
Resid. Foot FA 20.06 0.01 0.34
Gender 0.21 0.02 0.20
Age 0.41 0.19 ,0.0001*
Weight 20.15 0.01 0.35
Composite FA
Resid. Composite FA 20.18 0.05 0.046*
Gender 0.24 0.04 0.12
Age 0.42 0.20 ,0.0001*
Weight 20.12 0.01 0.44
FA values are residuals of the FA index on the athletes’ primary events. Results are shown first for individual traits (F
6,66
= 5.43, p,0.0001, adjusted r
2
= 0.27) and then for
composite FA (F
4,68
= 8.04, p,0.0001, adjusted r
2
= 0.28). P-values for the predicted relationship between FA and performance are directional (see Methods), and
statistical significance is indicated by asterisks.
doi:10.1371/journal.pone.0113106.t005
Figure 2. Boxplots for the three traits in athletes compared across events. These values reflect overall asymmetry, including FA and DA,
divided by trait size. Knees are represented by open bars, ankles by bars filled with diagonals, and feet by bars filled with dots. Circles represent
outliers, with stars indicating extreme outliers; color of circles and stars corresponds to coloring in bars.
doi:10.1371/journal.pone.0113106.g002
Symmetry in Elite Jamaican Athletes
PLOS ONE | www.plosone.org 7 November 2014 | Volume 9 | Issue 11 | e113106
running relies on oxygen much more than do sprints and
symmetrical organs of air intake should maximize consumption.
Foot asymmetry predicts physical aggressiveness in boys [24] and
lower body symmetry predicts the same for college undergraduates
[25], perhaps because stability is especially important in fights. Ear
asymmetry, in turn, predicts tendency for women and girls to
cradle a baby or doll, respectively, on the right side [3]. By
contrast, Tomkinson, Popovic
´and Martin [26] failed to find any
significant differences between elite football (soccer) and basketball
players, nor between elite (national league) and sub-elite (state
leagues) categories of each. This is not surprising given their
methodology. Numerous traits, soft body and hard, were
measured for symmetry in each individual, and then averaged
together so that a single average value was typically used. In our
own work, symmetry of one part of the body (knees) suggests
quality of associated parts as well, not just the bones of the knee
but the attached cartilage, muscle, associated structures and
developmental control. We know nothing about the details of this.
The only part of the sprinting apparatus thought in advance to be
important that we did not measure was the buttocks, hips, and
glutei maximi (the largest and strongest muscles in the human
body). Muscular strength measurements and imaging techniques
such as dual-energy X-ray absorptiometry may allow a chance for
progress on this (possibly key) variable.
A second problem has to do with cause and effect. If we find
that those elite sprinters with the best times also have the most
symmetrical knees, is it because those with symmetrical knees do
well in advance or is it that intensive training leads to both success
and more symmetrical knees? Of course it is likely that cause and
effect go in both directions, and there is a weak trend toward
decreased knee FA with age in the athletes (r = 20.15, p = 0.22).
However, the fact that 8 year old knee FA predicts sprinting ability
14 years later [1] and that there are no statistically significant
changes in symmetry with age in elite athletes, even though the
older will have exposed themselves to symmetrical forces during
training longer than the younger, suggests that knee symmetry is
by no means a mere reflection of training.
In addition to the positive effects of symmetry on running
performance that we demonstrate, we also find differences in
symmetry between running events. Runners specializing in longer
races are less symmetrical than sprinters, and this difference is
particularly noticeable for the ankles. Why this is the case is
unclear, but may relate to the asymmetrical stresses of events
requiring turns and an increased prevalence of rearfoot striking in
longer events, which would alter the distribution of stresses acting
on the joints [27].
Acknowledgments
We are most grateful for the personal interest of Jeffrey Epstein and
Gordon Getty. We thank Carla Hufschmidt and Tessa Cappelle for expert
help in the field and John Graham for advice on analysis.
Author Contributions
Conceived and designed the experiments: RT. Performed the experiments:
RT BF MR KM. Analyzed the data: BGP BF. Contributed reagents/
materials/analysis tools: RT BF MR KM BJ. Contributed to the writing of
the manuscript: RT BGP BF. Provided access to elite Jamaican athletes:
BJ.
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