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Repeatability of electro- and acoustic myographic activity during a fatigue test of normal lumbar paraspinal muscles

Department of Physiotherapy, University of Queensland, Australia

MJ Stokes

Department of Physiotherapy, University of Queensland, Australia

The repeatability of acoustic myography (AMG) and electromyography (EMG) of the paraspinal muscles of 15 healthy subjects was investigated during a fatigue test involving a sustained horizontal hold of the upper body against gravity. The AMG and EMG signals were full-wave rectified and integrated (IAMG, IEMG). The variability of recordings made during a 60-second isometric contraction performed on three different days was assessed by analysis of variance (ANOVA) and coefficients of variation (CVs) were calculated from the ANOVA. The IAMG: IEMG ratio was calculated to assess electromechanical uncoupling during fatigue and the IAMG and I EMG values were also normalized to a percentage of initial activity. At the beginning of the fatigue test, absolute values for IAMG and the IAMG:IEMG ratio were not as repeatable between days as IEMG (CVs = IAMG 18%, IEMG 11 %, IAMG: IEMG ratio 23.5%). Absolute values at the end of the test showed similar degrees of repeatability for each variable (CVs = IAMG 21 %, IEMG 10%, IAMG: IEMG ratio 24%). Normalized values at the end of the fatigue test were repeatable (CVs = AMG 6%, EMG 6%, AMG : EMG ratio 9%), but variability was observed during the contraction. The present results indicate that absolute values of EMG are more repeatable than AMG for assessing paraspinal muscle activity on different days in healthy subjects. The changes in normalized values were variable during fatiguing activity but repeatable at the end of the test. Further control of the AMG recording technique is required to refine the fatigue test before it can be applied as a clinical assessment tool.

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