Changes in Surface EMG of Biceps Brachii With Increasing Velocity of Eccentric Contraction in Women

Abstract

Twelve physically active women underwent a 3-week program involving eccentric, isotonic arm flexion at 120 to 180% of their maximal isometric arm flexion strength (MVC). They then performed 5 trials at 120, 140, 160, and 180% MVC. High-speed video ascertained the mean eccentric angular velocity of each trial. Bipolar surface electrodes recorded mean integrated electromyographic activity (IEMG), mean frequency and peak amplitude of electromyographic activity (EMG), and rate of occurrence of isolated, high-amplitude spikes to identify differences in recruitment patterns at different angular velocities. A one-way MANOVA suggested that all variables responded differently to the increasing loads, thus two-way ANOVAs were conducted for each variable. Mean angular velocity increased significantly from 120 to 140% MVC and then tended to plateau. Peak amplitude was significantly greater for 120% MVC than for the 3 higher load categories. Mean IEMG, mean frequency, and rate of spike occurrence did not differ significantly across conditions. These results were equivocal as to whether there were significant differences in recruitment patterns for maximal eccentric arm flexions for speeds between 0.18 and 0.25 rad · s–1.