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Using body size to understand the structural design of animals: quadrupedal locomotion
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1975
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Gait AnalysisMetabolic RateEngineeringFitnessMotor ControlStride LengthAnatomyLocomotor PerformanceMovement AnalysisQuadrupedal LocomotionKinesiologyBiomechanicsBio-inspired RoboticsBiostatisticsLegged RobotKinematicsHealth SciencesAnimal PhysiologyAllometric StudyDesignStructural DesignHuman Musculoskeletal SystemBipedal LocomotionBody SizeStride FrequencyPhysiologyExercise PhysiologyPathological GaitAnimal LocomotionHuman Movement
Gait and performance metrics in running quadrupeds, such as stride frequency, stride length, and oxygen uptake, scale as power‑law functions of body weight, yet measuring maximum speed is confounded by differing definitions and training effects. The study proposes theoretical models that maintain geometric, elastic, or static‑stress similarity across animals of varying body weights. By comparing animals at the physiologically similar trot‑gallop transition speed, the authors develop and evaluate these similarity models. The elastic‑similarity model best fits published data on body and bone proportions, surface area, metabolic rate, and heart and lung frequencies, and most accurately predicts stride frequency, stride length, limb excursion angles, and metabolic power at the trot‑gallop transition for species ranging from mice to horses.
Many parameters of gait and performance, including stride frequency, stride length, maximum speed, and rate of O2 uptake are experimentally found to be power-law functions of body weight in running quadrupeds. All of these parameters are reasonably easy to measure except maximum speed, where the question arises whether one means top sprinting speed or top speed for sustained running. Moreover, differences in training and motivation make comparisons of top speed difficult. The problem is circumvented by comparing animals running at the transition between trotting and galloping, a physiologically similar speed. Theoretical models are proposed which preserve either geometric similarity, elastic similarity, or static stress similarity between animals of large and small body weights. The model postulating elastic similarity provides the best correlation with published data on body and bone proportions, body surface area, resting metabolic rate, and basal heart and lung frequencies. It also makes the most successful prediction of stride frequency, stride length, limb excursion angles, and the metabolic power required for running at the trot-gallop transition in quadrupeds ranging in size from mice to horses.