Quadriceps femoris cross-sectional area and specific leg strength: relationship between different muscles and squat variations

Background. The aim was to determine the relationship between the cross-sectional area of the quadriceps femoris and strength performance in the deep and parallel barbell squat. Methods. The sample included 16 university students (seven female, 24.1 +/- 1.7 years). Muscle strength was expressed as external load, including the one-repetition maximum and the body mass segments involved (calculated according to Dempster's method). The cross-sectional area of the quadriceps femoris muscles was determined using ultrasound, while leg muscle mass was measured using the Bioelectrical Impedance method. Results. The cross-sectional areas of the three vastii muscles and leg muscle mass showed moderate to strong correlation with external load in both squat types (r = 0.509-0.873). However, partial correlation (cross-sectional area of quadriceps femoris muscles were controlled) showed significant association only between leg muscle mass and deep squat (r = 0.64, p < 0.05). The cross-sectional area of the vastus lateralis showed a slightly higher correlation with external load in the parallel than in the deep squat (r = 0.67, p < 0.01 vs. r = 0.59, p < 0.05). The regression analysis extracted the vastus medialis cross-sectional area as the most important factor in manifesting strength (parallel squat: R-2 = 0.569; deep squat: R-2 = 0.499, both p < 0.01). The obtained results suggest that parallel squat strength depends mainly on the cross-sectional area of the vastii muscles, while it seems that the performance in the deep squat requires an additional engagement of the hip and back extensor muscle groups.

Automated summary

The study showed that there is a moderate to strong correlation between the cross-sectional area of the quadriceps femoris and external load in both deep and parallel squats. Additionally, it was found that leg muscle mass is significantly associated with external load in the deep squat. The vastus lateralis had a slightly higher correlation with external load in the parallel squat compared to the deep squat, and the vastus medialis cross-sectional area was identified as the most crucial factor in manifesting strength in both squat types.