Contributions of Muscle Architecture and Tissue Properties to Knee Extensor Force Production.

Hirono, T, Murota, N, Tanaka, H, Yagi, M, Wang, Z, Mukai, H, Itsuda, H, and Ichihashi, N. Contributions of muscle architecture and tissue properties to knee extensor force production. J Strength Cond Res 39(12): e1371-e1379, 2025-Muscular characteristics, such as muscle size, fascicle length and angle, connective tissue within the muscle, and stiffness, are related to muscle force. This study aimed to investigate the contributions of these factors for isometric contraction strength in the quadriceps muscles using multivariate analyses. Maximal voluntary isometric strength of the quadriceps at 3 different knee angles (40, 70, and 100°) in 48 adults (24 men, 23.5 ± 3.0 years) was evaluated. The cross-sectional area (CSA), fascicle length, pennation angle, echo intensity, and shear elastic modulus of the quadriceps were evaluated using ultrasonography. Simple regression analyses revealed that CSA, echo intensity, shear elastic modulus, and fascicle length were significantly related to peak torque and rate of torque development (RTD). The peak torque during isometric contraction was significantly explained by CSA as an independent variable at all knee angles ( β = 0.445-0.732), but not by other variables (adjusted R2 = 0.457-0.678). The RTD as a dependent variable was explained by CSA at all angles ( β = 0.491-0.702), and by fascicle length at 100° of knee flexion ( β = 0.206), but not by other variables (adjusted R2 = 0.371-0.665). These results suggested that maximal isometric contraction strength was determined mainly by muscle CSA, not by other variables.