The effects of dorsiflexor and plantar flexor muscle fatigue on movement and muscle activity during single-leg relevés / Miranda Aman (2022)

Dance often requires repetitive movements throughout classes, rehearsals, and performances, which could impact the potential risk of injury via the effects of fatigue, both whole body and localized. Both muscle fatigue as well as repetitive movements can contribute to injury occurrence. While the rate of injury in dancers is well documented, the extent of how muscle fatigue affects physical performance of dancers remains understudied. Aim: This study investigates how muscle activation and movement alters as a result of dorsiflexor and plantar flexor muscle fatigue in dancers during single-leg relevés. Methods: 14 participants with current or recent experience in dance were recruited (26.64  4.30 years; 13 female and 1 male). All participants performed ten single-leg relevés before and after a fatigue protocol to a set tempo of 46 beats per minute. The protocol consisted of completing consecutive single-leg relevés with minimal balance support until a 50% drop in heel height occurred. Through the use of surface electromyography, the pre-fatigue and post-fatigue differences were assessed in the amplitude during the ascending and descending phases of the medial gastrocnemius, lateral gastrocnemius, soleus and the tibialis anterior. Data on kinematic variables, including ankle range of motion and heel height, were obtained and assessed using 3D motion capture technology. Data was checked for outliers prior to running statistical analysis. Paired t-tests were conducted to assess potential differences from the pre-fatigue phase to the post-fatigue phase. Additionally, a Shapiro-Wilks test was conducted to check for normal distribution of data. Lastly, the effect size was quantified by the use of Cohen’s d. Results: No significant muscle activation differences occurred from pre-fatigue to post-fatigue during the ascending phase. However, all muscles with the exception of the tibialis anterior increased in activation during the descending phase with significant differences in both the soleus (p = 0.02) and lateral gastrocnemius (p = 0.03). Additionally, ankle range of motion (p = 0.004) and heel height (p = 0.007) significantly decreased from pre-fatigue to post-fatigue. There was also a significant decrease in ankle dorsiflexion (p < 0.001) and plantar flexion (p = 0.014) post-fatigue. Conclusion: Overall, ankle plantar flexor fatigue results in an inability to maintain movement despite increased muscle activation. Future application of these results indicate that dancers should not continue to work past fatigue, as it could lead to increased mechanical compensations which increase the risk of injury. Considerations and duration of training or rehearsal should be made should be made by dancer, teachers, and choreographers in order to limit time spent dancing at or past the point of fatigue. Future research should investigate the frequency muscle fatigue is induced within dance classes, rehearsals, or performances. If the study were to be replicated, it is suggested that a standardized reliable protocol be put in place.