Michael A. Trevino1, Adam J. Sterczala2, Jonathan D. Miller3, Mandy E. Wray3, Hannah L. Dimmick3, and Trent J. Herda3.

1Oklahoma State University, Stillwater, OK; 2University of Pittsburg, Pittsburgh, PA; 3University of Kansas, Lawrence, KS.

PURPOSE: To examine the effects of continuous cycling on maximal aerobic capacity (VO2MAX), maximal strength (MVC) of the leg extensors, and MU behavior of the vastus lateralis (VL). METHODS: Thirteen females completed 20 training sessions. Pre- and post-training, participants performed a cycling VO2MAX test and MVCs on an isokinetic dynamometer followed by two consecutive submaximal (40% relative to pre-training MVC) contractions of the right leg extensors. Surface electromyographic (EMG) decomposition assessed recruitment thresholds (RT), motor unit action potential amplitudes (MUAPAMPS) and mean firing rates (MFR) for each observed MU from the VL for the 40% MVCs and linear regressions determined the y-intercepts (y-ints) and slopes for the MFR vs. RT and MUAPAMP vs. RT relationships. EMGRMS for the 40% MVCs was normalized (N-EMG) to the MVC for the current visit. Separate paired samples t-tests examined VO2MAX and MVC. Separate two-way ANOVAs (time x repetition) examined N-EMG and the y-ints and slopes for the MFR vs. RT and MUAPAMP vs. RT relationships. Follow-up analyses included Bonferroni corrections and alpha was 0.05. RESULTS: There were significant increases in VO2MAX (P < 0.001) and decreases in MVC (P = 0.030) post-training. For the y-ints from the MFR vs. RT relationships, there was a significant two-way interaction (P = 0.014). The y-ints for post-training were greater for repetition (rep) 1 than rep 2 (P = 0.007). For the slopes from the MFR vs. RT and MUAPAMP vs. RT relationships, there were no significant (P > 0.05) two-way interactions or main effects for time. There were main effects for rep (P < 0.05). The slopes were greater for rep 2 when collapsed across time. For N-EMG, there was no significant two-way interaction (P > 0.05). There were main effects for time (P = 0.017) and rep (P = 0.005). N-EMG was greater for post-training and rep 2 when collapsed across rep and time. CONCLUSION: Continuous cycling increased maximal aerobic capacity, decreased maximal strength of the leg extensors, and resulted in training and repetition dependent changes in MU firing rate behavior. Greater N-EMG suggests increased MU recruitment to match pre-training absolute torques. Continuous cycling may reduce the strength of the lower-threshold MUs, resulting in greater MU recruitment to match submaximal tasks.

ACKNOWLEDGEMENTS: This study was funded by the Doctoral Research Grant fund from the National Strength and Conditioning Association, Colorado Springs, CO

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