Chinguun Khurelbaatar1, Richard Yang1,2, Michael A. Bemben1, Daniel Larson1, & Christopher D. Black1, FACSM

1University of Oklahoma, Norman, Oklahoma; 2University of Oklahoma-Health Sciences Center, Oklahoma City, Oklahoma

There is evidence of cross-education of the repeated-bout effect (RBE) to the undamaged contralateral limb; but it is reduced in magnitude compared to what is observed in the ipsilateral limb. Mirror visual feedback (MVF) has been shown to augment the degree of cross-education observed with unilateral strength training, thus it is plausible MVF might augment cross-education of the RBE. PURPOSE: Therefore, the purpose of this study was to investigate if MVF could enhance the contralateral RBE following unilateral eccentric exercise. METHODS: Twenty-eight participants (14 women) performed 3 sets of 8 repetitions of maximal eccentric contractions with the elbow flexors on an isokinetic dynamometer with their dominant arm. They were then randomized into 3 groups: 1) control (CON), 2) no mirror (NM), and 3) mirror (MIR). CON performed a second bout of eccentric exercise two week later, again with their dominant arm. The NM and MIR each performed the second bout 1 week later. In the MIR group a mirror was placed along the midline of the body such that it created the illusion of bilateral exercise. Muscle damage was quantified using maximal isometric strength (MVC), range-of-motion (ROM) of the elbow flexors, and ratings of muscle soreness (DOMS). EMG was also recorded from the elbow flexors and extensors during each bout of eccentric exercise. RESULTS: CON (-26 ± 11 vs. -11 ± 11%) and NM (-39 ± 18 vs. -28 ± 13%) showed a RBE for change in MVC 48-hours after exercise (p < 0.02). MIR showed no change (-26 ± 21 vs. -24 ± 20%; p = 0.70). Similar patterns were observed for DOMS with CON (41 ± 20 vs. 17 ± 7) and NM (64 ± 24 vs. 53 ± 27) showing a RBE (p < 0.04) but not for MIR (49 ± 28 vs. 42 ± 29; p = 0.11). No differences were observed in ROM or EMG RMS across all groups between bouts (p>0.05). CONCLUSIONS: Our findings that MVF did not result in a contralateral RBE and therefore did not augment this effect compared to the NM group. This may have been due to a small sample size and the heterogenous nature of damage following eccentric exercise. Future studies should continue to investigate the use of a mirror to augment the contralateral RBE with larger sample sizes and assess the validity of different mirror placement positions.

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