Analysis of the electromyographic activity of human elbow joint muscles during slow linear flexion movements in isotorque conditions

Electromyograms were recorded by surface electrodes from the mm. biceps brachii (caput longum et breve), brachioradialis and triceps brachii (caput longum) in 10 healthy human subjects during slow linear movements in the elbow joint against a weak extending torque. The test movements were carried out under visual control through combining on a monitor screen a signal from a joint angle sensor with an appropriate command generated by a computer. The movements were fulfilled against a weak constant extending torque (0.5–2.5 Nm) and the extensor muscles were inactive. Surface electromyograms were full-wave rectified, filtered and averaged within sets of 10 identical tests. For the test movements in the range from 20° to 100° (0° corresponds to a completely extended joint in these designations) the dynamic components of the efferent commands to actively contracted muscles frequently had a well-expressed monotonous increase. The electromyography intensity during movement quite often increased exponentially in all three investigated flexors. At the same time, the averaged electromyograms in one or two muscles could contain non-monotonous oscillations, thus showing a well-expressed decrease in the intensity of the efferent inflow within a middle range of a movement phase. The non-monotonous oscillations could occur in some subjects under minimal loads (0.5–0.75 Nm); they usually appeared initially only in one muscle, whereas the frequency of their occurrence was not high. The probability of finding the non-monotonous oscillations in the electromyograms from the muscles under study increased with heightening the extending load. Under the loads of 2.0–2.5 Nm this type of reaction could be found in almost half of all records (for the three muscles in each of the 10 subjects under testing). The presence of noticeable non-monotonous components in the electromyograms of the elbow flexors during their contraction is probably connected to their biomechanical arrangement within the joint. It is known that the arms of the forces generated by elbow flexors are maximal in the middle range of joint angles and decrease with a change in angle in both directions. Thus, we can suppose that non-monotonous decrement components in the electromyograms of the elbow flexors are presumably connected with an obvious necessity for a subject to decrease the excitatory efferent inflow to the muscles in the middle range of the joint angles. The pattern of electromyograms in the flexors actin