Scaling of work and power in a locomotor muscle of a frog

Abstract

Muscle work and power are important determinants of movement performance in animals. How these muscle properties scale determines, in part, the scaling of performance during movements, such as jump height or distance. Muscle-mass-specific work is predicted to remain constant across a range of scales, assuming geometric similarity, while muscle-mass-specific power is expected to decrease with increasing scale. We tested these predictions by examining muscle morphology and contractile properties of plantaris muscles from frogs ranging in mass from 1.28 to 20.60 g. Scaling of muscle work and power was examined using both linear regression on log₁₀-transformed data (LR) and non-linear regressions on untransformed data (NLR). Results depended on the method of regression not because of large changes in scaling slopes, but because of changing levels of statistical significance using corrections for multiple tests, demonstrating the importance of careful consideration of statistical methods when analyzing patterns of scaling. In LR, muscle-mass-specific work decreased with increasing scale, but an accompanying positive allometry of muscle mass predicts constant movement performance at all scales. These relationships were non-significant in NLR, though scaling with geometric similarity also predicts constant jump performance across scales, because of proportional increases in available muscle energy and body mass. Both intrinsic shortening velocity and muscle-mass-specific power were positively allometric in both types of analysis. Nonetheless, scale accounts for little variation in contractile properties overall over the range examined, indicating that other sources of intraspecific variation may be more important in determining muscle performance and its effects on movement.