Effect of mechanical compression due to load carrying on shoulder muscle fatigue during sustained isometric arm abduction : an electromyographic study

摘要: The use of surface electromyography (EMG) for studying the effect mechanical compression occupational origin on muscle fatigue has been subject poor attention in ergonomic research. This study examined backpack carrying two shoulder muscles during sustained low force static contraction: middle deltoid (MD) and upper trapezius (UT) which strap exerted direct compressive force. EMG activities MD UT muscles, dominant non-dominant sides, were studied eight subjects tasks, a maximal an exhausting submaximal bilateral isometric 90° arm abduction, performed while load 0, 10, 20 kg, respectively. amplitude (root mean square, RMS) spectral (mean power frequency, MPF) parameters computed from recorded signals. No significant differences between sides found none whatever load-carrying mass. Load-carrying masses tested did not influence significantly abduction performance contrary to time exhaustion task, decreased with increasing A increase fatigability, defined by slope MPF decrease, was observed both when mass increased; but only presented level, value respect its initial value, at end task. Furthermore, activation UT, quantified RMS, task higher So, increased signs local may be interpreted localised blood flow impairment resulting this muscle.