Muscle activation during a reach-to-grasp movement in sitting position: influence of the distance.

The purpose of this study was to examine the influence of the reach distance on the muscle activation during a reach-to-grasp movement in the sitting position. Ten healthy male volunteers were tested. Surface EMG were recorded for the deltoid scapular, the deltoid clavicular, the triceps brachii, the biceps brachii and the brachioradialis. These muscles have been selected for their contribution to the cylindrical palmar prehension motion in the sagittal plane. Three distances have been tested: 20, 30 and 40 cm. For each distance, ten repeated measures have been recorded. From this in vivo data, the repeatability of the protocol has been tested. For this, relative (ICC) and absolute (SEM) reliabilities are determined in order to evaluate the intra operator repeatability of this protocol. It appears that the ICC values obtained are between 0.78 and 0.99 in all the conditions (15 conditions corresponding to three distances and five muscles). The intra operator repeatability is thus confirmed. From these surface EMG recordings the muscle activations have been calculated as the iEMG value. It appears that the muscle activation is greater with increased distances. The results contribute to the identification of the levels of muscle activation amplitude during a simple reach-to-grasp movement that is common in prehension research. This knowledge is essential in order to calculate the muscle forces and to integrate these forces in the prehension models developed nowadays in the robotic, rehabilitation, ergonomics field of research.