Central and Peripheral aspects of Fatigue Following 30s Maximal Exercise

Abstract

34 subjects throughout the day and the cold weather issues were resolved. School administrators should provide teachers with professional development when implementing a mandated policy.Electromyography (EMG) is used to study changes in muscle activation with fatigue. However, changes in EMG amplitude are also affected by changes in membrane properties (e.g., changes in ionic gradients). The muscle compound action potential (M-wave) is used normalize changes in EMG amplitude with fatigue. PURPOSE:To compare fatigue-induced M-wave changes of the vastus lateralis elicited by electrical (Estim) versus magnetic (Magstim) nerve stimulation. METHODS:Ten subjects underwent stimulation of the femoral nerve (3 magnetic and 3 electrical stimuli) prior to and following an isomeric knee extension contraction at 50% of maximal voluntary contraction (MVC). Subjects maintained the contraction until torque declined by 27Nm. EMG signals were recorded using bipolar pre-amplified electrodes and sampled at 2000 Hz. The M-waves were quantified by calculating the peak-to-peak (PtP) and the root mean square (rms) amplitude. The M-waves from each modality at each time period (pre and post isometric contraction) were averaged and the percent change in M-wave amplitude was calculated for each modality. The Estim and Magstim relationships were analyzed using Pearson correlation coefficients. RESULTS:The data from one subject was removed from the analysis because it was not possible to elicit valid M-waves from the magnetic stimulation. This was likely due to the adiposity of the subject. For PtP, the mean + SD M-wave amplitudes were: 1) Estim pre = 5274 + 3397 millivolts (mV), 2) Estim post = 5300.43 + 2727 mV, 3) Magstim pre = 5465 + 3076 mV, and 4) Magstim post 4972 + 2257 mV. For rms: Estim pre = 1081 + 697 mV, 2) Estim post = 1137 + 570 mV, 3) Magstim pre = 1124 + 585, and 4) Magstim post = 1063 + 500 mV. The Estim vs. Magstim amplitudes were highly correlated (all r > 0.90, p< .001), however the percent change scores were poorly correlated (PtP r = 0.46, p = .21; rms r = 0.66, p=.053). CONCLUSIONS:Estim and Magstim amplitudes were highly correlated with each other. Changes with fatigue were poorly correlated between modalities. A more severe fatiguing task may be necessary to more clearly examine the relationships between modalities with fatigue. (No relationships reported)An important factor contributing to loss of function and reduced mobility in the elderly is skeletal muscle fatigue, which is a poorly understood and underappreciated consequence of aging. Mechanisms of muscle fatigue are not clearly understood in the elderly population and accordingly, exercise regimes are not optimized to maximize both muscle and physical performance in this expanding population. PURPOSE:To determine the response of the quadriceps femoris (QF) of young and older women to fatiguing protocols that utilize either maximum voluntaryor neuromuscular electrical stimulation-induced (NMES) contractions. METHODS:Twelve young (20 ± 1.03 years, 166 ± 6.7 cm, ...