Optimal body size and limb-length ratios associated with 100-m PB swim speeds

Purpose: To identify optimal body size and limb segment-length ratios associated with children and adolescents' 100 m personal-best swim speeds. Methods: Fifty national-standard youth swimmers (21 males, 29 females, ages 11-16 years, mean age +/- SD = 13.5 +/- 1.5 years) participated in the study. Anthropometry comprised stature, body mass, skinfolds, maturity offset, upper arm, lower arm and hand lengths and upper leg, lower leg and foot lengths. Swimming performance was taken as the personal best (PB) time/speeds for the 100 m freestyle swim recorded in competition. To identify the optimal body-size and body-composition components associated with 100 m personal-best (PB) swimming speeds (having controlled for age and maturity offset), we adopted a multiplicative allometric log-linear regression model, refined using backward elimination. Results: Lean body mass was the singularly most important whole-body characteristic. Stature and body mass did not contribute to the model, suggesting that the advantage of longer levers was limb specific rather than a general whole-body advantage. The allometric model also identified that having greater limb segment-length ratios, i.e., the arm ratio=(low arm)/(upper arm) and the foot-leg ratio=(foot)/(lower leg) was key to PB swimming speeds. Conclusions: It is only by adopting multiplicative allometric models that the above ratios could have been derived. The advantage of having a greater lower arm is clear but to have, at the same time, a shorter upper arm (achieved by adopting a closer elbow-angle technique or possessing a naturally endowed shorter upper arm) is a new insight into swimming performance. A greater foot-to-lower leg ratio suggests that a combination of larger feet and a shorter lower-leg length may also benefit PB swim speeds. Publisher statement: This is a non-final version of an article published in final form in Nevill, A.M. , Oxford, S. and Duncan, M.J. (2015) Optimal body size and limb-length ratios associated with 100-m PB swim speeds. Medicine and Science in Sports and Exercise, volume 47 (8): 1714–1718. See http://dx.doi.org/10.1249/MSS.0000000000000586 for the published version.