Comparative Adaptations to Different Leg Extension Set-termination Strategies in Trained Men and Women: A Unilateral Within-Participant Study

Abstract

Vasconcelos, T, Ruivo, A, Refalo, MC, Chaves Lucas, G, Vasconcelos, PR, Brito, JP, Vilaça-Alves, J, and Oliveira, R. Comparative adaptations to different leg extension set-termination strategies in trained men and women: A unilateral within-participant study. J Strength Cond Res XX(X): 000–000, 2026—The purpose of this study was to compare relative adaptations between two set-termination strategies (momentary muscular failure vs. repetitions in reserve) using a unilateral within-participant design under ecologically realistic resistance-training conditions. Nineteen trained subjects (11 men, eight women; mean age: 22.3 ± 3.9 years; body mass: 69.9 ± 10.3 kg) completed an 8-week unilateral intervention. Each subject performed leg extensions, with one limb randomly assigned to the FAIL protocol and the contralateral limb to the repetitions-in-reserve (RIR) protocol. Muscle thickness (ultrasound) of the knee extensors and 1-repetition maximum strength were assessed pre- and postintervention and analyzed using Bayesian linear mixed-effect models. Estimated between-protocol differences for hypertrophy were negligible (knee extensors: −0.019 cm [−0.094 to 0.054]), as were differences for 1-repetition maximum strength (knee extensors: 0.198 kg [−1.87 to 2.6]). Secondary analyses using standardized mean differences also suggested no clear overall advantage for either protocol. These findings suggest that resistance training performed with a 1- to 3-RIR may produce adaptations comparable with training to momentary muscular failure in knee extensors under applied training conditions. Strength and conditioning professionals may therefore consider RIR-based strategies as a practical approach to manage fatigue while maintaining training effectiveness.