The Effects of Repetition-Matched Resistance Training to Failure Versus Non-Failure on Local Muscular Endurance

Background/Objectives: The present study aimed to compare the improvement in lower-extremities local muscular endurance following moderate-intensity resistance exercise performed either as two sets to momentary failure or as four repetition-matched non failure sets. Methods: Fifteen physical education students (10 males, 5 females; age: 21.9 ± 3.1 years, body mass: 71.2 ± 11.4 kg, height: 1.74 ± 0.08 m) completed a counterbalanced within-participant unilateral trial comparing two resistance training conditions: failure (two sets performed to momentary failure with one lower extremity) and non-failure (the same total number of repetitions distributed across four sets with the contralateral extremity). Both conditions involved leg press exercise at 50% of their one repetition maximum (1RM), performed three times per week for four weeks. Local muscular endurance, leg-press 1RM, quadriceps cross-sectional area (CSA), and body composition were assessed before and after training. Results: Absolute and relative muscular endurance increased significantly after training in both lower extremities (Failure: 105.9 ± 57.54%; 56 ± 44.57%, p < 0.001; Non-failure: 76.7 ± 42.10%; 33.9 ± 30.75%, p < 0.001, respectively), with significant differences between them (p < 0.05, ηp2 = 0.458 and 0.322, respectively). Leg press 1RM and quadriceps CSA increased significantly (Failure: 20 ± 14.21%; 11.2 ± 7.33%, p < 0.001; Non-failure: 20.5 ± 9.92%; 10.7 ± 6.10%, p < 0.001, respectively), with no significant differences between conditions (p > 0.05). Conclusions: Training to momentary failure elicited significantly greater increases in local muscular endurance than the repetition-matched non-failure protocol. However, these results suggest that repetition-matched, non-failure protocols offer an effective alternative for improving local muscular endurance, while producing increases in maximum strength and muscle size, with no statistically significant differences between conditions, in young, physically active adults without systematic resistance training experience.