Motor control of the reaction time during simultaneous hand grip and elbow flexion

Abstract

Reaction time was measured during simultaneous elbow flexion and hand grip contractions in 14 subjects. The results were summarized as follows:

1) The hand grip in the simultaneous condition showed a longer reaction time (RT), while no difference was found in RT for the elbow flexion. Premotor time (PMT) was increased both in the hand grip and elbow flexion. Motor time (MT) of the elbow flexion revealed a decrease, but no difference was found in MT of the hand grip.

2) Elbow flexion in the simultaneous condition exhibited decrements in peak force and maximum rate of force in crease, while no changes were observed in the hand grip.

3) Irrespective of whether the EMG onset of a distal muscle (flexor digitorum superficialis) was earlier than a proximal muscle (biceps brachii) or vice versa, the onset of the force was earlier for the proximal elbow flexion than the distal hand grip.

From these results, it is suggested that the increase of PMT and the force decrease in the elbow flexion during simultaneous condition are caused by some mechanism of central nervous system, while the earlier force onset of the elbow flexion even though the EMG started earlier for the distal muscle are due to the function of multiarticular muscles associated with both distal and proximal joint movements.