Electromyographic activities of muscles in the shoulder and elbow joints during elbow flexion-extensions with different velocities in the sagittal and horizontal planes

Abstract

Study aim: Properly processed surface electromyographic signals (EMGs) provide a suitable means for the estimation of muscle activity, including their synergistic and antagonistic action. This study aimed to investigate changes in the activity of elbow and shoulder muscles due to changes in the velocities of elbow flexion/extension motions in the sagittal and horizontal plane without and with an additional load of 0.5 kg on the wrist using processed EMGs of six muscles and the angle of the elbow joint.

Material and methods: Experimental data from ten healthy volunteers were processed. The EMGs from each part of a motor task – maximal elbow flexion from an initial downwards arm position, rest in the maximally flexed position and maximal extension – were filtered, rectified, and normalized according to suitable maximal isometric tasks. The areas under the obtained curves for each part, called activities, were subjected to statistical analysis including calculations of correlation coefficients between the activities of different muscles.

Results: In general, muscle activities were heterogeneous and strongly individual. The angular velocity was higher for movements without additional weight. Sagittal flexion velocity was higher than the horizontal one. The muscle activities for all subjects for all muscles are presented and discussed.

Conclusions: The main conclusions were as follows: m. biceps brachii, m. brachialis and m. deltoideus pars clavicularis showed the main activity, and their activity increased with increasing velocity but not with increasing load; m. deltoideus pars spinata and m. triceps brachii had slow activity. Surprisingly, the small m. anconeus was much more active than the m. triceps, especially during extension.