THE EFFECTS OF MUSCLE LENGTH ON FORCE STEADINESS AND EMG RESPONSES FOLLOWING A FATIGUING PROTOCOL

Abstract

The purpose of this study was to examine the effect of muscle length on force steadiness and EMG responses following a fatiguing intervention. Twenty-three subjects, fifteen men and eight women, were required to perform isometric contractions of their dominant forearm flexors at both 60 degrees of elbow flexion and 90 degrees of elbow flexion. The protocol consisted of three pre-fatigue MVC’s, two pre-fatigue submaximal trapezoid contractions set at 50% MVC, a fatiguing protocol, three post-fatigue MVC’s, and finally two post-fatigue trapezoid contractions. The subjects performed this protocol at both joint positions, and each position was tested on separate visits to the laboratory. During all contractions, data were collected for force and EMG signal of the biceps brachii. The findings of this study indicated that the 60 degree flexion position produced a less steady submaximal contraction than the 90 degree flexion position during both pre and post fatiguing submaximal contractions. The results also indicated that there were no significant differences in EMG responses during submaximal contractions between the two joint positions tested. In conclusion, the present study suggests that force steadiness may be reduced when a muscle is in a lengthened position when compared to a shortened position and this phenomenon may not be due to neural changes during the contractions.