Which regions of the quadriceps femoris muscle thickness best predict muscle strength?

The study aimed to investigate the associations between regional muscle thickness (MT) of the rectus femoris (RF) and vastus lateralis (VL) and muscle strength during leg press and knee extension exercises. Twenty-eight men (23 ± 5 years) participated in this cross-sectional study. MT was assessed using ultrasound at the proximal (1/3), middle (1/2), and distal (2/3) regions between the anterior superior iliac spine and the superior border of the patella over the RF muscle, with lateral projection onto the VL. Maximum isotonic muscle strength was assessed using one-repetition maximum (1RM) tests in the leg press and knee extension exercises. Moderate, positive, and statistically significant correlations were observed for most comparisons (r = 0.408-0.655, P < 0.05), except for the association between leg press 1RM and distal RF MT, which was weak and not statistically significant (r = 0.366, P = 0.056). Multiple regression analyses indicated that proximal RF and VL MTs explained a greater proportion of the variance in leg press strength (R2 = 0.421, P < 0.01), whereas proximal and distal VL MTs explained a greater proportion of the variance in knee extension strength (R2 = 0.511, P < 0.01). These findings suggest that regional quadriceps femoris MTs are differentially associated with strength performance depending on the exercise performed in young men. Proximal RF and VL regions best predicted leg press strength, whereas VL thicknesses, particularly at the proximal and distal regions, were more strongly associated with knee extension strength.