A comparison of volume-equated knee extensions to failure, or not to failure, upon rating of perceived exertion and strength adaptations

The present study aimed to compare the effects of repetition duration-, volume-, and load-matched resistance training to muscular failure (MMF) or not to muscular failure (NMF) on maximal voluntary isometric knee extensor strength. This design also allowed testing of the efficacy of "5x5" training. Nine recreationally active males (age, 21.4 +/- 1.2 years; height, 1.79 +/- 0.07 m; weight, 78.4 +/- 7.1 kg) performed unilateral resistance training at 80% of maximal torque at 2x/week for 6 weeks. Using their nondominant leg, participants performed 5 sets of 5 repetitions (NMF). Using their dominant leg, participants performed 25 repetitions in as few sets as possible (MMF). All repetitions were performed at a pace of 2 s concentric, 1 s isometric pause, and 2 s eccentric with a 2-min rest interval between sets. Analyses identified significant pre-to post-intervention strength increases for both MMF and NMF, with effect sizes (ESs) of 2.01 and 1.65, respectively, with no significant differences between conditions (p > 0.05). Peak and mean ratings of perceived exertion (RPEs) were significantly higher for MMF compared with NMF conditions (p < 0.0001), and a tendency for significantly higher RPE values reported for later sets for the NMF condition. Total training time per session was significantly longer for NMF compared with MMF (p < 0.001). The present study suggests that in untrained participants, resistance training NMF produces equivocally the same strength increases as training to MMF when volumematched. However, resistance training to MMF appears to be a more time-efficient protocol and may produce greater strength gains as indicated by a larger ES.