Reconsidering the effects of respiratory constraints on the optimal running speed.
BACKGROUND
Although both humans and quadrupeds frequently coordinate breathing and limb movement during running, early studies in humans focused on how increased breathing flexibility in humans allowed for relaxed or even transient coordination during locomotion. This difference was used to explain why quadrupeds had an optimal running speed whereas humans did not. Recent research, however, has clearly demonstrated that humans, like quadrupeds, have an optimal running speed. Because these findings are new, it remains unclear why this is true: whether because entrainment in humans was more important than initially predicted or because another restraint is acting. Here, we try to explain the observed minimum cost of transport (CoT) by analyzing metabolic cost with respect to entrainment and a standard set of anthropometrics.


METHODS
We measured the energetic cost of human running at five different speeds and calculated individual CoT curves for each participant (N = 9). Simultaneously, entrainment was determined by the degree to which a poststimulus histogram (breaths per 0.05-s bin after a footfall) differed from a uniform plot.


RESULTS
We compared the degree of entrainment to each participant's optimal running speed and found that although all of our subjects clearly entrained at some speeds, entrainment was not a function of CoT (P = 0.897). Because entrainment was also not correlated with speed (P = 0.304), it seems that bipedalism removed the respiratory constraints associated with quadrupedalism as originally suggested.


CONCLUSIONS
Unlike quadrupeds, for whom respiratory constraints remain implicated in the speed dependence of CoT, constraints that lead to a minimum CoT for people must involve other mechanisms of efficiency such as the storage and release of energy in the lower limbs.
Department of Biology, Seattle Pacific University, Seattle, WA, USA. michael.willcockson@gmail.com
Michael A
MA
Willcockson
Cara M
CM
Wall-Scheffler
D000886:Anthropometry; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008660:Metabolism / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D012119:Respiration; D012420:Running / Q000502:physiology* / Q000592:standards*; D055815:Young Adult