Determine scaling rules for optimal fiber length across sex, age, and size

Determine the rules governing how optimal fiber length scales with sex, age, and body size in human lower-limb muscles to enable a reliable translation from experimentally measured muscle mass to physiological cross-sectional area for musculoskeletal modeling.

Background

PCSA is often computed from muscle mass or volume divided by optimal fiber length. However, measuring optimal fiber length directly is difficult, and many modeling workflows assume simplified scaling (e.g., proportional to segment length), which recent evidence suggests may be inaccurate. In particular, prior work indicates that while muscle mass scales with body mass, fiber length does not, complicating translation from mass to PCSA.

The authors explicitly state that the rules for scaling optimal fiber length with sex, age, and size remain unclear, preventing a direct and generalizable conversion from muscle mass to PCSA across demographic groups. Establishing these rules is essential for demographically accurate strength parameterization in musculoskeletal models.