Comparison of Muscle Hypertrophy and Strength Adaptations Induced by Back Squat and Leg Extension Resistance Exercises

ABSTRACT Kassiano, W, Costa, B, Kunevaliki, G, Lisboa, F, Prado, A, Alves, L, Tricoli, I, Stavinski, N, Francssuel, J, and Cyrino, ES. Comparison of muscle hypertrophy and strength adaptations induced by back squat and leg extension resistance exercises. J Strength Cond Res XX(X): 000–000, 2025—Exercise selection affects muscular adaptations (e.g., strength gains and muscle hypertrophy). The purpose of this study was to compare changes in strength and muscle size between the back squat and leg extension resistance exercises. Sixty-three untrained young women were randomly allocated to perform the Smith machine back squat (SQ, n = 30) or leg extension (LE, n = 33) exercises. Subjects performed 3 sets of 8–12 repetitions maximum (RM) per session, 2 d·wk −1 , for 8 weeks. Muscle thickness of the rectus femoris (RF) and vastus lateralis (VL) was measured at the proximal, middle, and distal sites. Strength was assessed through 3 repetitions maximum (3RM) tests in the back squat (3RM-SQ) and leg extension (3RM-LE) exercises. The LE experienced greater increases in the 3 RF sites (proximal: +11.4% vs. +2.0%; middle: +12.3% vs. +5.7%; distal: 17.5% vs. +7.9%; all p < 0.001). Conversely, the SQ showed greater increases in VL at the distal site (+18.2% vs. +11.2%; p < 0.001). Smith machine back squat induced greater increases in 3RM-SQ (+46.7 vs. 21.3%; p < 0.001), but no between-group difference was observed in 3RM-LE increases (SQ = +19.8% vs. LE = +23.4%; p = 0.824). Based on our results, the leg extension induce greater rectus femoris hypertrophy, while the back squat promotes greater vastus lateralis hypertrophy, particularly at the distal site. The back squat training seems to be more effective for increasing squat strength, but both exercises are likely similarly effective for increasing leg extension strength.