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MECHANOMYOGRAPHIC AMPLITUDE-FORCE RELATIONSHIPS FOR THE VASTUS LATERALIS ARE ALTERED FOLLOWING 10 WEEKS OF AREOBIC CYCLING

Abstract

S. Feng*1, M.A. TrevinoƗ2, J.D. MillerƗ1, A.J. SterczalaƗ1, and T.J. Herdaǂ1

1University of Kansas, Lawrence, KS, 2Armstrong State University, Savannah, GA

It has been suggested the mechanomyographic amplitude (MMGRMS)-force relationship may characterize motor unit (MU) recruitment and firing rate behavior of muscle. A log -transformation of this relationship has differentiated aerobically- from resistance-trained and sedentary individuals. To date, it remains unclear when alterations in MU behavior occur following aerobic training. PURPOSE: The purpose of this study was to examine the effects of 10 weeks of aerobic cycling training on absolute maximal aerobic capacity (VO2MAX), maximal strength (MVC) for the leg extensors, and the MMGRMS-force relationships for the vastus lateralis (VL). METHODS: Thirteen sedentary individuals (mean ± SD, age = 22.31 ± 5.34 yrs) completed 40 aerobic cycling training sessions over 10 weeks. Weeks 1 – 3 consisted of 30 mins of cycling at 70% of heart rate reserve (HRR), whereas, weeks 4 – 6 and 7 – 10 were 40 mins at 75% and 80% of HRR. Pre – and post-testing included VO2MAX, and MVC on an isokinetic dynamometer followed by a submaximal (70% relative to pre-training MVC) linearly increasing muscle action of the leg extensors. Prior to testing, an MMG sensor was placed over the VL and the MMG and force signals were simultaneously sampled at 2 kHz and were bandpass filtered (4th order Butterworth) at 5-100 Hz. For the linearly increasing muscle action, linear regression models were fit to the log-transformed MMGRMS-force relationships and the slope (b term) was calculated. Separate paired samples t-tests were used to examine absolute VO2MAX, MVC, and the b terms. An alpha level was set at 0.05 to determine statistical significance. RESULTS: There was a significant increase (P<0.001) in absolute VO2MAX (Pre=2.41±0.82 ml/min, Post=2.75±088 ml/min) following 10 weeks of aerobic cycling training. For MVC, there was no significant difference (P=0.442) from pre- (150.17±46.38 Nm) to post-training (147.30±48.46 Nm). The b terms significantly increased (P=0.039) following 10 weeks of aerobic cycling training (Pre=0.502±0.209 m s-2/Nm, Post=0.601±0.222 m s-2/Nm). CONCLUSION: Ten weeks of aerobic cycling improved maximal aerobic capacity with no significant change in maximal strength. However, greater b terms for the MMGRMS-force relationships likely indicated increased motor unit recruitment to match pre-training absolute torques.

This work was supported in part by a National Strength and Conditioning Association Foundation (NSCAF) Graduate Research Doctoral Grant.

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