Ing-Shiou Hwang1,2, Yen-Ting Lin3, Chien-Chun Huang4, Yi-Ching Chen5,6. 1. Institute of Allied Health Sciences, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan. 2. Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan, 70101, Taiwan. 3. Physical Education Office, Asian University, Taichung, 41354, Taiwan. 4. Medical Device Innovation Center, National Cheng Kung University, Tainan, Taiwan. 5. Department of Physical Therapy, College of Medical Science and Technology, Chung Shan Medical University, Taichung, 40201, Taiwan. yiching@csmu.edu.tw. 6. Physical Therapy Room, Chung Shan Medical University Hospital, Taichung, 40201, Taiwan. yiching@csmu.edu.tw.
Abstract
PURPOSE: This study investigated fatigue-related modulation of common neural inputs to motor units (MUs) under 5 Hz, which determines force precision control. METHODS: Twenty-seven adults performed a sequence of fatiguing contractions. The participants were assessed with a static isometric index abduction at 20% maximal voluntary contraction in the pre-test and post-test. Discharge characteristics of MUs of the first dorsal interosseous muscle were analyzed with decomposed EMG signals. RESULTS: Along with increases in the mean (58.40 ± 11.76 ms → 62.55 ± 10.83 ms, P = 0.029) and coefficient of variation (0.204 ± .014 → 0.215 ± 0.017, P = 0.002) in inter-spike intervals, the fatiguing contraction caused reductions in the mean frequency (16.84 ± 3.31 Hz → 15.59 ± 3.21 Hz, P = 0.027) and spectral dispersions (67.54 ± 4.49 → 62.64 ± 6.76 Hz, P = 0.007) of common neural drive, as estimated with smoothed cumulative motor unit spike trains (SCMUSTs). Stabilogram diffusion analysis of SCMUSTs revealed significant fatigue-related reductions in the long-term effective diffusion coefficient (1.91 ± 0.77 Hz2/s → 1.61 ± 0.61 Hz2/s, P = 0.020) and long-term scaling exponent (0.480 ± 0.013 Hz2/s → 0.471 ± 0.017 Hz2/s, P = 0.014). After fatiguing contraction, mutual information of force fluctuations and SCMUSTs was augmented roughly by 12.95% (P = 0.041). CONCLUSIONS: Muscular fatigue could compress and shift the low-frequency common drive to MUs toward lower spectral bands, thereby enhancing transmission of twitch forces through the muscle-tendon complex with a low-pass filter property. The fatigue-induced changes involve increased closed-loop control of the common modulation of MU discharge rates.
PURPOSE: This study investigated fatigue-related modulation of common neural inputs to motor units (MUs) under 5 Hz, which determines force precision control. METHODS: Twenty-seven adults performed a sequence of fatiguing contractions. The participants were assessed with a static isometric index abduction at 20% maximal voluntary contraction in the pre-test and post-test. Discharge characteristics of MUs of the first dorsal interosseous muscle were analyzed with decomposed EMG signals. RESULTS: Along with increases in the mean (58.40 ± 11.76 ms → 62.55 ± 10.83 ms, P = 0.029) and coefficient of variation (0.204 ± .014 → 0.215 ± 0.017, P = 0.002) in inter-spike intervals, the fatiguing contraction caused reductions in the mean frequency (16.84 ± 3.31 Hz → 15.59 ± 3.21 Hz, P = 0.027) and spectral dispersions (67.54 ± 4.49 → 62.64 ± 6.76 Hz, P = 0.007) of common neural drive, as estimated with smoothed cumulative motor unit spike trains (SCMUSTs). Stabilogram diffusion analysis of SCMUSTs revealed significant fatigue-related reductions in the long-term effective diffusion coefficient (1.91 ± 0.77 Hz2/s → 1.61 ± 0.61 Hz2/s, P = 0.020) and long-term scaling exponent (0.480 ± 0.013 Hz2/s → 0.471 ± 0.017 Hz2/s, P = 0.014). After fatiguing contraction, mutual information of force fluctuations and SCMUSTs was augmented roughly by 12.95% (P = 0.041). CONCLUSIONS: Muscular fatigue could compress and shift the low-frequency common drive to MUs toward lower spectral bands, thereby enhancing transmission of twitch forces through the muscle-tendon complex with a low-pass filter property. The fatigue-induced changes involve increased closed-loop control of the common modulation of MU discharge rates.
Authors: Markus Amann; Simranjit K Sidhu; Joshua C Weavil; Tyler S Mangum; Massimo Venturelli Journal: Auton Neurosci Date: 2014-10-23 Impact factor: 3.145