The influence of moment arm of the muscle on myoelectric activity

Abstract

[Purpose] The purpose of this study was to investigate the influence of moment arm of the muscle on the myoelectric activity. [Methods] The subjects included 104 upper-limbs of 52 healthy young adult males. They held the weight in 3 different positions (25, 70, 120 degrees) of elbow flexion since the previous studies reported that the 70 degrees of the elbow flexion became the longest moment arm of the biceps brachii muscle, and 25 and 120 degrees had nearly same moment arm. We measured the myoelectric activity on the biceps brachii muscle, then calculated IEMG of the interval during subjects’ holding the weight for 1 second, and normalized with a value of maximum contraction (%IEMG). For the statistical analysis, repeated measure analysis of variance was applied as well as Bonferroni method for multiple comparisons. [Results] The %IEMG in 70 degrees showed the significant low value in comparison with 25 or 120 degrees. The %IEMG in 120 degrees was significant lower than one in 25 degrees. [Conclusion] This study suggested that it was necessary to consider the influence of the difference in moment arm of the muscle when physical therapists interpreted the value of myoelectric activity of the muscle.