Investigation of localized muscle fatigue

Muscle fatigue is a condition where the ability of the muscle to contract and produce force is reduced. Generally the result of prolonged, relatively strong muscle activity, localized muscle fatigue (LMF) occurs when a muscle or a group of muscles has reduced ability to contract and produce force despite neural stimulation. The causes of physical fatigue include poor workplace practices and lack of regular physical exercise. Signs of fatigue include reduced motivation, blurred vision, increased reflex time and poor concentration – all elements in fatigue-related accidents. Muscle fatigue is a leading cause of workplace and transport-related accidents, as well as work-related musculoskeletal disorders.<br>This thesis reports on an experimental study conducted to determine the effects of LMF on the physiological signals produced during voluntary isometric and cyclic muscle contraction. Surface electromyography (SEMG) was considered relevant for this research because it is the most practical and non-invasive technique for recording such physiological signals. Time and frequency domain responses were extracted from recorded signals and analysed. <br> Statistical analysis on extracted data was carried out using analysis of variance (ANOVA) and non parametric (sign-test) analysis. Sign-test analysis shows a statistically significant change in root-mean-square (RMS) amplitude both before and after the onset of fatigue during cyclic contraction but no statistically significant change in median frequency (MDF). But for isometric contraction the results of sign-test show that there is a statistically significant change in both MDF and RMS before and after the onset of fatigue. Similarly, ANOVA results suggest that for isometric contraction there is a statistically significant change in both MDF and RMS before and after the onset of fatigue. In addition, there is a statistically significant change in RMS amplitude before and after the onset of fatigue during cyclic contraction but no statistically significant change in MDF. <br>The results clearly demonstrate that while SEMG analysis is appropriate for muscular fatigue detection, the use of MDF alone does not provide a reliable and valid measure for LMF detection in real world applications where most tasks require a combination of both isometric and cyclic contractions.<br>