Time course of muscle hypertrophy with and without progressive overload

Abstract

To compare the time course of muscle hypertrophy during resistance training with progressive overload (PROG) or without overload progression (N-PROG), 31 healthy untrained young adults completed a randomized within-subject trial. Each participant trained one leg with PROG and the contralateral leg with N-PROG using unilateral knee extension (3x10–12 repetitions, twice weekly for 12 weeks). Load was progressively adjusted in PROG and kept constant in N-PROG. Muscle cross-sectional area (mCSA) was assessed at Pre and after sessions 6, 12, 18, and 24. A protocol×time interaction was observed for mCSA (p=0.002). Both protocols increased mCSA from Pre to S24 (PROG: 3.36±1.94 cm²; N-PROG: 2.67±1.86 cm²), with no significant between-protocol differences in mCSA at the individual assessment time points. However, the increase in mCSA from S18 to S24 was greater in PROG than in N-PROG (between-protocol difference in change: 1.22 cm², 95% CI 0.59 to 1.84; p<0.001). Repetitions in reserve (RIR) was 0.47±0.61 at S1 and 0.20±0.37 at S24 in PROG, and 1.50±1.11 and 4.08±1.94, respectively, in N-PROG. Overall volume load and perceived exertion were greater in PROG (p<0.001). The PROG protocol maintained high relative effort, and the greater increase in mCSA compared with N-PROG was observed specifically from S18 to S24.