Similar muscle hypertrophy following eight weeks of resistance training to momentary muscular failure or with repetitions-in-reserve in resistance-trained individuals.
Level 2 - randomized trial
Individual randomized within-subject trial
PubMed 38393985 · doi:10.1080/02640414.2024.2321021
What was done
Eighteen resistance-trained adults (12 males, 6 females) completed an 8-week resistance training program (2 sessions per week) involving leg press and leg extension exercises. In a within-subject design, each participant's lower limbs were randomized to train to momentary muscular failure (FAIL) or to a target proximity-to-failure of 1 to 2 repetitions-in-reserve (RIR; 2-RIR for leg press, 1-RIR for leg extension). Muscle thickness of the rectus femoris (RF) and vastus lateralis (VL) was assessed pre- and post-intervention, alongside acute neuromuscular fatigue (repetition and lifting velocity loss), using Bayesian linear mixed-effects models.
What was found
Increases in mean quadriceps thickness (average of RF and VL) were similar between conditions: 0.181 cm (HDI: 0.119 to 0.243) for FAIL and 0.182 cm (HDI: 0.115 to 0.247) for RIR. Between-protocol differences in RF thickness slightly favored RIR at -0.036 cm (HDI: -0.113 to 0.047), while VL thickness slightly favored FAIL at 0.033 cm (HDI: -0.046 to 0.116). Mean training volume was similar between conditions. Lifting velocity loss and repetition loss were consistently greater in FAIL compared to RIR.
Why it matters
Stopping resistance sets 1 to 2 repetitions short of failure elicits quadriceps hypertrophy comparable to training to complete momentary failure over 8 weeks, while generating less acute neuromuscular fatigue.
Limits
The sample size was small (n = 18), and the intervention lasted only 8 weeks. Testing was limited to two machine exercises (leg press and leg extension) and quadriceps hypertrophy, precluding conclusions about upper-body musculature or free-weight compound exercises. Proximity-to-failure was based on perceived RIR, which may introduce subjective error.
Cited by
- supports Resistance training volume can be traded off against proximity to failure, such that performing extra sets while leaving several repetitions in reserve produces muscle hypertrophy comparable to fewer sets taken to complete muscular failure.
- context Research by Refalo assessing muscle swelling at 3 and 5 days post-exercise indicates that high-volume hypertrophy gains reflect true muscle tissue accretion rather than sustained edema.