The importance of comparative physiology: mechanisms, diversity and adaptation in skeletal muscle physiology and mechanics

Skeletal muscle powers animal movement, making it an important determinant of fitness. The classic excitation-contraction coupling, sliding-filament and crossbridge theories are thought to describe the processes of muscle activation and the generation of force, work and power. Here, we review how the comparative, realistic muscle physiology typified by Journal of Experimental Biology over the last 100 years has supported and refuted these theories. We examine variation in the contraction rates and force-length and force-velocity relationships predicted by these theories across diverse muscles, and explore what has been learnt from the use of workloop and force-controlled techniques that attempt to replicate aspects of in vivo muscle function. We suggest inclusion of features of muscle contraction not explained by classic theories in our routine characterization of muscles, and the use of phylogenetic comparative methods to allow exploration of the effects of factors such as evolutionary history, ecology, behavior and size on muscle physiology and mechanics. We hope that these future directions will improve our understanding of the mechanisms of muscle contraction, allow us to better characterize the variation in muscle performance possible, and enable us to infer adaptation.

Automated summary

In this article, the authors review the research conducted in the field of experimental biology over the past 100 years, examining how it has both supported and challenged the classic theories regarding muscle activation and force generation. They explore the variation in contraction rates and force-length and force-velocity relationships predicted by these theories across different muscles, and discuss the inclusion of muscle contraction features not explained by the classic theories in routine muscle characterization. They also propose the use of phylogenetic comparative methods to study the effects of factors such as evolutionary history, ecology, behavior, and size on muscle physiology and mechanics.