Establish scaling rules for optimal fiber length across sex, age, and size and enable translation from muscle mass to PCSA

Establish the quantitative scaling rules that relate optimal muscle fiber length to sex, age, and body size in human lower-limb muscles, and derive a reliable method to translate measured muscle mass (Mm) or muscle volume (Vm) to physiological cross-sectional area (PCSA) under those demographic conditions so that strength parameters can be accurately specified in musculoskeletal models.

Background

PCSA is often inferred from muscle volume or mass combined with optimal fiber length, yet fiber length is difficult to measure in vivo and frequently estimated via scaling assumptions. Recent results indicate that fiber length does not scale proportionally with muscle length, challenging common practices.

Because optimal fiber length scaling laws by sex, age, and size are not established, the paper notes there is no direct translation from muscle mass to PCSA across demographic groups. This gap prevents accurate demographic-specific strength parameterization in musculoskeletal models.