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# Title:        The Symmetry of Children's Knees is Linked to Their Adult Sprinting
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=== SUMMARY ===
The Symmetry of Children's Knees is Linked to Their Adult Sprinting Speed and their Willingness to Sprint in a Long-term Jamaican Study Trivers, R.i Palestis, B.2 & Manning, J.T.3' 'Department of Anthropology, Rutgers University, New Jersey, USA. 2Wagner College New York, USA. ;Applied Sports Technology Exercise and Medicine Research Centre, Swansea University, UK. *Correspondence should be addressed to: Abstract: Jamaican athletes are prominent in sprint running but the reasons for their succes


=== EXTRACTED TEXT ===
The Symmetry of Children's Knees is Linked to Their Adult Sprinting 
Speed and their Willingness to Sprint in a Long-term Jamaican Study 
Trivers, R.i Palestis, B.2 & Manning, J.T.3' 
'Department of Anthropology, Rutgers University, New Jersey, USA.  2Wagner College 
New York, USA. ;Applied Sports Technology Exercise and Medicine Research Centre, 
Swansea University, UK. 
*Correspondence should be addressed to: 
Abstract: Jamaican athletes are prominent in sprint running but the reasons for 
their success are not clear. Here we consider the possibility that symmetry, 
particularly symmetry of the legs, is high in Jamaican children and that this is 
linked to high sprinting speed in adults. Our study population was a cohort of 285 
rural children (156 boys), mean age 8.18(1.72) years. Symmetry was measured in 
1996 and 2006 from the fluctuating asymmetry (FA) of nine traits (six upper- and 
three lower-body traits) and we constructed an upper and a lower body composite 
FA trait [Comp ub:FA and Comp lb=FA respectively). We found Comp lb:
FA<Comp ub:FA, and both were lower than in comparable Caucasian norms. In 
2010 we measured sprinting speed (mean time for  90m and 180m races) in 
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participants recruited from our original cohort. There were 160 untrained adults in 
our sample, we found: (i) high Comp lb and knee symmetry in 1996 and 2006 were 
linked to fast sprinting times in our 2010 runners and (ii) our sample of sprinters 
appears to have self-selected for greater symmetry.  We conclude that Jamaican 
children have high symmetry in the legs, and that high knee symmetry is linked to 
an thin() to sprint fast in adult Jamaicans as well as a readiness to sprint. 
Caribbean sprinters, particularly Jamaican sprinters, have long been prominent in elite 
sprint running. However, the reasons for their disproportionate success in relation to the 
population size from which they are drawn are unclear. For example, ethnic comparisons 
of ACTN3 and ACE genotypes (1), mitochondrial haplotypes (2) and vertical jump and 
stride number/height ratio (3) have been made with mixed success. 
Here we take a different approach and focus on long-term symmetry, and in 
particular symmetry of the legs, and its relationship to adult sprinting speed in rural 
Jamaicans. Our measure of symmetry is fluctuating asymmetry or FA. FA consists of 
small departures from perfect bilateral symmetry in such paired traits as finger length, 
knee circumference and foot length (4). FA has been shown to be a negative correlate of 
running speed in horses (5) and humans (6). With regard to FA in Jamaicans, the 
Jamaican Symmetry Project (JSP) has focussed on long-term correlates of FA in a rural 
cohort of 288 Afro-Caribbean children (7). The children were first measured in 1996 
(when their mean age was 8.18 (1.72) years) and again in 2006. In 1996 nine paired traits 
were found to show FA (six upper body traits; ear height, finger length [3nd, 4th & 5'h 
fingers], wrist and elbow width: three lower body traits; knee and ankle circumference, 
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foot length). A tenth trait, hand width, showed significant directional asymmetry and was 
discarded. It was found that composite FA of the lower body (Comp .1b-FA) was much 
lower (-35%) than a composite measure of upper body FA (Comp ubzFA), and a 
comparison of FA in this sample with a large Caucasian sample of UK children showed 
lower FA in the former compared to the latter (7-9). 
Here we tested whether symmetry in children (particularly symmetry of the legs) 
is related to their running speed when they are young adults. In order to consider this, we 
recruited adult participants in 2010 from our original 1996 cohort. The original cohort 
was asked to volunteer for further tests and informed that they would have to complete 
two sprints. Using the FA's measured in 1996 and 2006, we then examined the 
relationships between trait FA's and sprinting speed recorded in 2010 and also  compared 
the Comp ubzFA and Comp lbzFA of the participants that did not volunteer to run with 
those that di&Our prediction was two-fold, i.e. (i) that FA measured in 1996 (and 2006) 
would be positively correlated with sprinting speed recorded in 2010 and (ii) that those 
that chose to run in 2010 would have been more symmetrical (particularly in the legs) in 
1996 than those that chose not to run. 
Methods 
The cohort was contacted by letter (reinforced by word-of-mouth) and informed of the 
aims of the study. The work was approved by the Human Subjects Committee of Rutgers 
University. In this rural area there was not a conventional running track available. 
Therefore, we constructed one which was 90metres long. Our two races were 90m and 
180m long (back and forth on the 90m track). The second race (180m) was run about a 1/2
hour after the first race. Subjects were run in pairs (same-sex whenever possible), in 
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order to increase competition during the run. When we had no one with whom to pair 
with a subject, he or she ran against a dummy runner of the same sex.  Mean sprinting 
time of 90m + 180m was calculated and used as our measure of performance. 
Results 
Descriptive statistics 
From the original cohort of 285 children (156 boys) we recruited 160 untrained adults (97 
men) in our sample. Means (SD) were as follows: age 23.56 (SD 1.81) years, sprinting 
time 23.60 (5.09) sec.. Males tended to run faster than females (males 20.60 [2.97] sec., 
females [28.21[4.12]sec.,  t = 13.66, p X0.0001), 
Relative FA 
The repeatability of signed absolute FA was significant for all traitsf7). With regard to 
measurements of the original cohort, relative FA (IL-RIAL+R*0.5) was calculated for 
each of the traits. Principal Components Analysis revealed five factors that accounted for 
66% of the variance in FA's. An orthogonal transformation showed factor 1 (17% 
variance) was related to lower body traits (knee r = 0.66, ankle r = 0.68, foot r = 0.64). 
The remaining factors were associated with one trait each (e.g. factor 2 13% variance, 4D 
r = 0.86; factor 3 13% variance 3D r = 0.87; factor 4 12% 3D r = 0.80; factor 5 II% r = 
0.93). Two composite FA traits were constructed, Comp ub:FA and Comp lb:FA by 
calculating the mean of all upper body FA's for the former and all lower body FA's for 
the latter. Comp ub:FA (0.022 [0.007]) was significantly greater than Comp lb :FA with 
very large effect size (0.008[0.006]), paired it test x-y = 0.014, t = 23.36,p = 0.0001, 
Cohen's d = 2.15). There was a significant sex difference in Comp ub:FA such that males 
(0.021[0.007], n = 152) were more symmetric than females (0.023[0.008], n = 126, t = 
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3.10, p = 0.002, d = 0.46), but Comp lb FA showed no significant sexual dimorphism 
(males n = 144, 0.007[0.006], females n = 126, 0.008[0.006], 1= 0.27,p = 0.79, d = 
0.17). 
1996 and 2006 Lower Body FA and 2010 running speed 
We removed the influence of BMI from lower body FA by regressing FA (Comp lb-FA, 
knee FA, ankle FA & foot FA) from 1996 and 2006 on their current BMI and then 
considered the relationships between residuals (Res FA) and sprinting speed (Table 1). 
We found that Res Comp Ib-FA was positively related to sprinting speed in 1996 (p = 
0.04) and 2006 (p = 0.04). Furthermore, a multiple regression analysis with independent 
variables Res knee FA, Res ankle FA and Res foot FA, showed Res knee FA was 
positively related to sprinting speed in 1996 (p = 0.02) and 2006 (p = 0.04). We then 
calculated mean FA from 1996 and 2006 and regressed this on mean BMI from 1996 and 
2006. The residuals from this regression showed significant positive relationships to 2010 
sprinting times (Res Comp Ib-FA (p = 0.04) and Res knee FA (p = 0.01). 
Relative FA in runners and those that did not run 
Our participants in the 2010 sprints numbered 157 individuals from our original cohort of 
270 children. We considered whether these volunteers showed evidence of self-selection 
for high lower body symmetry by comparing 1996 Comp Ib-FA of runners and non-
runners in 2010. We found that runners had lower Comp lb-FA (mean = 0.0052) than 
non-runners (mean =  0.00073, t = 2.87, p = 0.005; Table 2). This finding suggested that 
children with symmetrical lower bodies were more likely to engage in sprinting when 
adults than children with more asymmetrical lower bodies. 
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In addition to the initial recruitment of our cohort in 1996 and the 2010 sprinting 
recruitment, there have been five other recruitments (1998, 2002, 2004, 2005, and 2006) 
which have focussed on a variety of target variables. There was no evidence for 
significant self-selection on the basis of lower body FA for the years of 1998, 2002, 2005 
and 2006. The one exception to this finding was the 2004 recruitment. In common with 
2010, the 2004 volunteers showed lower Comp Ib-FA (mean =  0.00070) in comparison to 
non-volunteers (mean =  0.0088, t = 2.14.p = 0.03). In this instance the target trait in 2004 
was dancing ability_(Table 2). 
Conclusions 
We have the following findings: 
Our original cohort of rural Jamaican children, measured in 1996, had high levels 
of symmetry (i.e. low FA) in comparison to Caucasian children of similar ages (7-9). In 
particular, lower body traits (knee, ankle & foot FA) showed high symmetry. These 
findings were at a mean age of 8.18 (1.72) years. 
Some 14 years later, we attempted to recruit the entire cohort in order to measure 
sprinting speed. We found our new sub-set of participants showed evidence of self-
selection. Symmetry of the legs was greater in our 2010 sample of volunteers  in 
comparison to the non-volunteers of that year. This effect suggests that Jamaican children 
with high symmetry in the legs, will readily take part in sprints when they are young men. 
We think the importance of this finding relates to the enjoyment of sprinting. In addition, 
although our sample was untrained this evidence of self-selection may map-on to a 
readiness to train for sprinting events.  A similar effect was found in 2004 when 
participants were asked to volunteer for dancing. We suggest that the traits necessary for 
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successful sprinting may in part map on to traits that are important in dancing. More 
sedentary target traits were tested in 1998. 2002. 2005. and 2006. In these years 
volunteers and non-volunteers did not show significant differences in Comp lb-FA. 
We found that lower body FA measured  in 1996 and 2006 were positively related 
to sprinting performance in 2010. This was found for Comp Ib-FA and the effect was 
driven by the association between knee FA and sprinting times. That is, children with 
symmetric knees in 1996 and 2006  ran faster than children  with asymmetric knees when 
tested for sprinting speed in 2010. This effect was independent of other asymmetries in 
the legs. 
There are clear links here between childhood symmetry of the lower body and 
both motivation to sprint and ability to sprint well among rural Jamaicans. The effect is 
all the more remarkable for the intervening period of 14 years between the first 
measurements of leg symmetry and self-selection and performance effects related to 
sprinting. We suggest that high symmetry in the legs-especially knees—may underlie at 
least some of the advantage that Jamaican sprinters enjoy over their Caucasian 
competitors. 
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References 
I. Scott RA, Irving R, Irwin L, Morrison E, et al (2010) ACTN3 and ACE genotypes 
in elite Jamaican and US sprinters. Med Sci Sports Exerc 42: 107-112.8 
2. Deason M, Scott R, Irwin L, Macaulay V et al (2012) Importance of 
mitochondrial haplotypes and maternal lineage in sprint performance among 
individuals of West African ancestry. Scan J Med Sci Sports 22: 217-223. 
3. Babel K, Hertog C, Hue O (2005) Influence of ethnic origin on predictive 
parameters of performance in sprint running in prepubertal boys. In J Sports Med 
26: 798-802. 
4. Van Valen L (1962) A study of fluctuating asymmetry. Evolution 16: 125-142. 
5. Manning JT, Ockenden L (1994) Fluctuating asymmetry in racehorses. Nature 
370: 185-186. 
6. Manning JT, Pickup LJ (1998) Symmetry and performance in middle distance 
runners. Int J Sports Med 19: 1-5. 
7. Trivers R, Manning JT, Thornhill R, Singh D, McGuire M (1999) Jamaican 
symmetry project: Long-term study of fluctuating asymmetry in rural Jamaican 
children. Human Biology 71: 417-430. 
8. Wilson JM & Manning JT (1996) Fluctuating asymmetry and age in children: 
evolutionary implications for the control of developmental stability. Journal of 
Human Evolution., 30: 529-537. 
9. Manning JT, Wood D (1998) Fluctuating asymmetry and aggression in boys. 
Human Nature 9: 53-65. 
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10. Ruxton M. (2006). The unequal variance I-test is an underused alternative to 
Student's 1-test and the Mann—Whitney U test. Behavioral Ecology 17: 688-690. 
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Table 1 
Relationships (standardised regression coefficients, h)  between relative FA's independent 
of BMI (Res Comp lb-FA; Res FA knee; Res FA ankle; Res FA foot) and sprinting speed 
in 2010. Significant positive associations with sprinting speed were found for FA's 
measured in 1996 and 2006 and for mean FA's of 1996 + 2006. 
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Year n b 2 
1996 
Res Comp Ib-FA 147 0.17 0.04* 
Res FA knee 147 0.20 0.02* 
Res FA ankle 147 -0.03 0.72 
Res FA foot 147 0.10 0.21 
2006 
Res Comp Ib-FA 135 0.18 0.04* 
Res FA knee 135 0.18 0.04* 
Res FA ankle 135 0.06 0.52 
Res FA foot 135 0.09 0.32 
1996 + 2006 
Res Comp Ib-FA 124 0.21 0.02* 
Res FA knee 124 0.23 0.01* 
Res FA ankle 124 0.02 0.81 
Res FA foot 124 0.12 0.19 
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Table 2 
Mean Comp lb-FA for 1996 and for volunteers fin bold)  and non-volunteers for 
recruitments in years 1998, 2002, 2004, 2005, 2006 and 2010. There was evidence for 
unequal variances between the samples for volunteers and non-volunteers in 2004 and 
2010. Therefore, we used the unequal variance t-test (10). Volunteers had significantly 
lower Comp lb-FA than non-volunteers in year 2004 when recruitment was for dancing, 
and 2010 when recruitment was for sprinting. 
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Year Mean LBFA N SD SE t -df p 
1996 0.0076 270 0.0062 0.0004 
N/A 
1998 0.0073 139 0.0060 0.0005 0.61 263 0.54 
0.0078 131 0.0065 0.0006 
2002 0.0072 173 0.0062 0.0005 1.26 197 0.21 
0.0082 97 0.0063 0.0006 
2004 0.0070 187 0.0059 0.0004 2.14 138 0.034* 
0.0088 83 0.0068 0.0007 
2005 0.0070 151 0.0063 0.0005 1.69 257 0.092 
0.0083 119 0.0061 0.0006 
2006 0.0072 168 0.0060 0.0005 1.33 197 0.19 
0.0082 102 0.0066 0.0007 
2010 0.0066 157 0.0052 0.0004 2.87 190 0.005* 
0.0089 113 0.0073 0.0007 
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