Quadriceps muscle volume positively contributes to ACL volume.

Females have smaller anterior cruciate ligaments (ACLs) than males and smaller ACLs have been associated with a greater risk of ACL injury. Overall body dimensions do not adequately explain these sex differences. This study examined the extent to which quadriceps muscle volume (VOL ) positively predicts ACL volume (VOL ) once sex and other body dimensions were accounted for. Physically active males (N = 10) and females (N = 10) were measured for height, weight, and body mass index (BMI). Three-Tesla magnetic resonance images of their dominant and nondominant thigh and knee were then obtained to measure VOL , quadriceps, and hamstring muscle volumes, femoral notch width, and femoral notch width index. Separate three-step regressions estimated associations between VOL and VOL (third step), after controlling for sex (first step) and one body dimension (second step). When controlling for sex and sex plus BMI, VOL , notch width, or notch width index, VOL consistently exhibited a positive association with VOL in the dominant leg, nondominant leg, and leg-averaged models (p < 0.05). Findings were inconsistent when controlling for sex and height (p = 0.038-0.102). Once VOL was included, only notch width and notch width index retained a statistically significant individual association with VOL (p < 0.01). Statement of Clinical Significance: The positive association between VOL and VOL suggests ACL size may in part be modifiable. Future studies are needed to determine the extent to which an appropriate training stimulus (focused on optimizing overall lower extremity muscle mass development) can positively impact ACL size and structure in young females.