| Abstract | Recent data shows that for fatiguing isometric contractions, females are typically more fatigue resistant than males. However, there is limited data for dynamic contractions, specifically in aerobically trained individuals. PURPOSE: To investigate force and electromyographic (EMG) activity during and after a fatiguing unilateral resistance exercise protocol for the knee extensors in an aerobically trained population. METHODS: Twenty-three participants (22 right leg dominant; mean age = 24; 10 males; aerobically trained ~300mins/wk) visited the laboratory on two days separated by = 72 hrs. On the first visit, maximal dynamic strength was determined for the dominant (fatigued) leg and control procedures for maximal isometric strength of the non-dominant (non-fatigued) leg was performed. On the second visit, participants completed 4 sets of unilateral dynamic knee extensions to failure with 50% 1RM with 2 minutes rest intervals between sets. Maximal voluntary contractions (MVC) and EMG activity of the knee extensors were recorded immediately before exercise and after each set for both legs, except for set 1 and set 3, where only the fatigued leg performed MVC’s. MVC’s were also performed during acute recovery at 2.5mins, 5mins, and 10mins post exercise. Separate repeated measures ANOVA tests were performed on the MVC and EMG responses for each leg. Repeated measures ANOVA and independent samples t-test was performed for total repetitions completed. Alpha was set at 0.05. RESULTS: The results of the analysis show that for the fatigued leg, normalized MVC values significantly declined from Baseline to Set 1 (p<0.001; 91%), Set 2 (p<0.001; 90%), Set 3 (p<0.001; 86%), and Set 4 (p<0.001; 83%). Maximal strength recovered significantly more (p < 0.05, Cohen’s d = 0.602) at Recovery 3 (90%) versus Recovery 1 (86%). There was no significant change in EMG activity when comparing males to females. EMG amplitude significantly decreased from Baseline to Set 2 (p<0.05; 90%), Set 3 (p<0.01; 86%), and Set 4 (p<0.001; 82%) in the fatigued leg, and significantly increased during the recovery phase from Recovery 1 (72%) to Recovery 3 (p<0.01;85%), as well as from Recovery 2 (73%) to Recovery 3 (p<0.01; 85%). For the non-fatigued leg, there was a significant time by visit interaction (p = 0.011). EMG amplitude was significantly lower on the fatigue visit versus the control visit during Set 4 (p=0.048) and Recovery 1 (p=0.031). CONCLUSION: Following acute resistance exercise performed to failure of the lower body, no differences between males and females in fatigue and recovery was seen in this study, which contradicts current literature. Practical scenarios such as knee extensions to failure in an aerobically trained population may not reflect the sex-based differences in fatigue observed during isometric tasks. |
