Muscle Fiber Cross-Sectional Area Is Associated With Quadriceps Strength and Rate of Torque Development After ACL Injury

Abstract Graham, MC, Thompson, KL, Hawk, GS, Fry, CS, and Noehren, B. Muscle fiber cross-sectional area is associated with quadriceps strength and rate of torque development after ACL injury. J Strength Cond Res 38(6): e273–e279, 2024—The purpose of this study was to investigate the relationship between muscle fiber type–specific properties of the vastus lateralis and quadriceps muscle performance in individuals after an anterior cruciate ligament (ACL) tear. 26 subjects (22.0 ± 5.4 years) were included in this cross-sectional study, and all data were collected before ACL reconstruction. Quadriceps peak torque (QPT) and early (0–100 ms) and late (100–200 ms) rate of torque development (RTD) were obtained from maximal voluntary isometric quadriceps strength testing. Muscle fiber cross-sectional area (fCSA) and percent fiber type distribution (FT%) were evaluated through immunohistochemical analysis of a muscle biopsy. Between-limb differences in fiber characteristics were assessed using paired t-tests (with α-level 0.05). Relationships between fiber-specific properties and quadriceps muscle performance were determined using separate multiple linear regression analyses for ACL-injured and noninjured limbs. There were significant differences in fCSA between ACL-injured and noninjured limbs across all fiber types, but no differences in FT%. Type 1 fCSA, type 2a fCSA, and their interaction effect were the explanatory variables with the strongest relationship to all performance outcomes for the ACL-injured limb. The explanatory variables in the ACL-injured limb had a significant relationship to QPT and late RTD, but not early RTD. These findings suggest that QPT and late RTD are more heavily influenced by fCSA than FT% in ACL-injured limbs. This work serves as a foundation for the development of more specific rehabilitation strategies aimed at improving quadriceps muscle function before ACL reconstruction or for individuals electing nonsurgical management.