Research
Terrestrial locomotion
Scaling of maximum running performace
The relationship between locomotor performance and body mass in terrestrial mammals does not follow a single linear trend when the entire range of body mass is considered. Large taxa tend to show different scaling exponents compared to those of small taxa, suggesting that there would be a differential scaling between small and large mammals. I obtained estimations of maximum running speed for 142 species of mammals of several orders, spanning a wide range of sizes. The scaling of relative locomotor performance proved to be non-linear when the entire range of body masses was considered and showed a differential scaling between small and large mammals. Among the small species, a negative, although nearly independent, relationship with body mass was noted. In contrast, maximum relative running speed in large mammals showed a strong negative relationship with body mass. This reduction in locomotor performance was correlated with a decrease in the ability to withstand the forces applied on bones and may be understood as a necessary stress reduction mechanism for assuring the structural integrity of the limb skeleton in large species.
Gait transitions in rodents
The transition from trot to gallop in quadruped mammals has been widely hypothesized to be a strategy to minimize the energetic costs of running. This view, however, has been challenged by some experimental evidence suggesting instead that this transition might be triggered by mechanical cues, and would occur when musculoskeletal stresses reach a certain critical value. In this study we evaluated the effect of carrying loads on the locomotor energetics and gait transitions of the rodent Octodon degus running on a treadmill. Metabolic rate and cost of transport increased about 30% with a 20% increment in body mass. This increment was higher than expectations based on other mammals, where energy consumption increases in proportion to the added mass, but similar to the response of humans to loads. No abrupt change of energy consumption between gaits was observed and therefore no evidence was found to support the energetic hypothesis. The trot–gallop transition speed did not vary when subjects were experimentally loaded, suggesting that the forces applied to the musculoskeletal system do not trigger gait transition.
Biomechanics of bat flight
Mechanics of turning
Most flying organisms turn by rolling their bodies into a bank, thus orienting the lift produced laterally and generating a side or centripetal force. By examining fruit bats performing 90-degree turns in a flight corridor, we found that bats turn not only by banking their bodies but also by orienting the thrust component towards the direction of the turn. This is achieved by rotating the body around the center of mass during the upstroke in such a way that at the beginning of the downstroke, the body is already oriented into the turn. As a consequence, during the downstroke, both lift and thrust are going to contribute to the generation of centripetal force. Such a mechanism is expected to improve turning performance with respect to turns where only lift is used to produce centripetal force.
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