Author(s): LIBARDI, C.A., FERRARI, O., SILVA, D.G., CAMARGO, J.B.B., BITTENCOURT, D., MELO, A.C.C., IASULAITIS, M., PEREIRA, B.K.R., NACAFUCASACO, E.T.A., BERGAMASCO, J.G.A., Institution: FEDERAL UNIVERSITY OF SÃO CARLOS, Country: BRAZIL, Abstract-ID: 2328

INTRODUCTION:
Progressive overload is widely recommended in resistance training (RT) guidelines (1). However, no randomized controlled trial has directly tested whether the absence of overload progression compromises the time course of muscle hypertrophy.
METHODS:
Thirty-one untrained participants completed 12 weeks (24 sessions) of RT using a within-subject design. Individuals’ legs were randomized into two training protocols: 1) load progressively adjusted to maintain the target repetition zone over the training sessions (PROG); and 2) no load progression throughout the intervention (N-PROG). Repetitions were maintained within a 10–12 repetition maximum zone for both protocols. Vastus Lateralis (VL) muscle cross-sectional area (mCSA) was assessed via ultrasound at baseline (W0), week 3 (W3), week 6 (W6), week 9 (W9), and week 12 (W12). Volume load (sets × repetitions × load), perceived exertion (OMNI) and repetitions-in-reserve (RIR) were recorded each session and then summarized week-by-week. Repeated-measures analysis was performed to compare the effects of both protocols across the intervention for VL mCSA. Areas under curve (AUCs) (trapezoidal method) for volume load, OMNI, and RIR were compared using paired t-tests.
RESULTS:
A significant protocol × time interaction was observed for mCSA (p = 0.02). Both protocols increased mCSA over time (p < 0.05). However, only PROG showed a significant increase from W9 to W12 (p = 0.01), whereas N-PROG plateaued during this period (p > 0.05). Additionally, volume load, OMNI and RIR AUCs (across weeks) were greater in PROG than N-PROG (p < 0.001).
CONCLUSION:
RT without progressive overload promoted meaningful hypertrophy in the early weeks (nine weeks). However, continued hypertrophic gains in later phases occurred only with load progression. These findings suggest that progressive overload may not be essential for early adaptations in untrained individuals, but becomes important for sustaining muscle growth over time.