Strength Training with Repetitions to Failure Does Not Provide Additional Neuromuscular Adaptations in Young Women

Abstract

Results regarding the effectiveness of training until concentric failure in improving neuromuscular adaptations are still controversial and there are few data on its effects in muscle hypertrophy. PURPOSE: This study investigated the effects of 10-week resistance training to failure on neuromuscular adaptations in young women. METHODS: 89 active young women (21.9 ± 3.3 yrs) were randomly assigned to one of three groups: 1) repetitions to failure (RF; n = 30, three sets of repetitions to failure at 70% of 1RM); 2) repetitions not to failure with equalized volume (RNFV; n = 32, four sets of 7 repetitions at 70% of 1-RM); and 3) repetitions not to failure (RNF; n = 27, three sets of 7 repetitions at 70% of 1RM). The training volume from the RNFV group was the same as the RF group. All groups performed the elbow flexor exercise and met 2 days per week. The outcome assessed included the maximal strength (1RM), muscular endurance, peak torque (PT) at 60°.s-1 and 180°.s-1, and muscle thickness (MT). Differences between and within groups were analyzed using two-way analysis of variance (ANOVA), with alpha level of p<0.05. RESULTS: There were significant increases (P<0.05) in muscle strength after 5 (15.9% for RF, 18.4% for RNF, and 19.9% for RNFV) and 10 (28.3% for RF, 26.8% for RNF, and 28.3% for RNFV) weeks of training, with no significant differences between groups. Muscular endurance increased after 5 (74.8% for RF, 85.8% for RNF, and 80.3% for RNFV) and 10 weeks (117.4% for RF, 103.5% for RNF, and 128.8% for RNFV), with no differences between groups. PT increased significantly at 60°.s-1 in the RNFV group (10.2%), whereas no changes were observed in the RF (9.0%) and RNF (1.7%) groups. Significant increases were observed in the peak torque at 180°.s-1 in the RNFV (13.7%) and RNF (4.1%) groups, whereas no changes were observed in the RF group (-0.5%). MT increased significantly in the RF and RNF groups after 5 (RF: 8.4%, and RNFV: 2.3%, P<0.05) and 10 weeks of training (RF: 17.5%, and RNFV: 8.5%, P<0.05), whereas no changes were observed in the RNF group. CONCLUSIONS: Repetitions to failure do not yield additional overall neuromuscular improvements. However, when performing submaximal repetitions, the training volume must increase (i.e., adding more sets) to optimize the overall neuromuscular adaptations in young women.