2 research outputs found
Ultra-endurance athletic performance suggests that energetics drive human morphological thermal adaptation
Both extinct and extant hominin populations display morphological features consistent with Bergmann's and Allen's Rules. However, the functional implications of the morphologies described by these ecological laws are poorly understood. We examined this through the lens of endurance running. Previous research concerning endurance running has focused on locomotor energetic economy. We considered a less-studied dimension of functionality, thermoregulation. The performance of male ultra-marathon runners (n = 88) competing in hot and cold environments was analysed with reference to expected thermoregulatory energy costs and the optimal morphologies predicted by Bergmann's and Allen's Rules. Ecogeographical patterning supporting both principles was observed in thermally challenging environments. Finishers of hot-condition events had significantly longer legs than finishers of cold-condition events. Furthermore, hot-condition finishers had significantly longer legs than those failing to complete hot-condition events. A degree of niche-picking was evident; athletes may have tailored their event entry choices in accordance with their previous race experiences. We propose that the interaction between prolonged physical exertion and hot or cold climates may induce powerful selective pressures driving morphological adaptation. The resulting phenotypes reduce thermoregulatory energetic expenditure, allowing diversion of energy to other functional outcomes such as faster running
Energetics as a driver of human morphological thermal adaptation; evidence from female ultra-endurance athletes
Functional benefits of the morphologies described by Bergmann’s and Allen’s rules in human males have
recently been reported. However, the functional implications of ecogeographical patterning in females
remain poorly understood. Here, we report the findings of preliminary work analysing the association
between body shape and performance in female ultramarathon runners (n = 36) competing in hot and
cold environments. The body shapes differed between finishers of hot and cold races, and also between
hot race finishers and non-finishers. Variability in race performance across different settings supports the
notion that human phenotype is adapted to different thermal environments as ecogeographical patterns
have reported previously. This report provides support for the recent hypothesis that the heightened
thermal strain associated with prolonged physical activity in hot/cold environments may have driven
the emergence of thermally adaptive phenotypes in our evolutionary past. These results also tentatively
suggest that the relationship between morphology and performance may be stronger in female vs. male
athletes. This potential sex difference is discussed with reference to the evolved unique energetic context
of human female reproduction. Further work, with a larger sample size, is required to investigate the
observed potential sex differences in the strength of the relationship between phenotype and performance