Review of the methods used for calculating physiological cross-sectional area (PCSA) for ecological questions

This review examines literature that used physiological cross-sectional area (PCSA) as a representative measure of an individual muscle's maximal isometric force production. PCSA is used to understand the muscle architecture and how a trade-off between muscle force and muscle contractile velocity reflect adaptations of the musculoskeletal system as a reflection of functional demands. Over the decades, methods have been developed to measure muscle volume, fascicle lengths, and pennation angle to calculate PCSA. The advantages and limitations of these methods (especially the inclusion/elimination of pennation angle) are discussed frequently; however, these method descriptions are scattered throughout the literature. Here, we reviewed and summarised the different approaches to collecting and recording muscle architectural properties to subsequently calculate PCSA. By critically discussing the advantages and limitations of each methodology, we aim to provide readers with an overview of repeatable methods to assess muscle architecture. This review may serve as a guide to facilitate readers searching for the appropriate techniques to calculate PCSA and measure muscle architecture to be applied in ecomorphology research. RESEARCH HIGHLIGHTS Discuss the theories behind PCSA in a synthesised review to inform researchers about PCSA methodology.