Hiroshi Nagasaki

PREMOTOR AND MOTOR REACTION TIME AS A FUNCTION OF FORCE OUTPUT

The effects of variation in force output on fractionated reaction times (RTs) in elbow extension for 5 normal adults were examined. Force was manipulated by instructing the subject to respond with much or little force, and force output was measured by an accelerometer. Premotor RT increased with increased force output, indicating that organization of force for movement could affect not only the movement speed but the timing of its initiation. Motor RT became longer at manipulated force production than the control response, suggesting that motor RT was also influenced by the central processing of movement organization. The early electromyographic activities of the triceps brachii muscle were examined and discussed in relation to the production of force for initiation of movement.

Timing and rate of development of tension produced by the fast voluntary contraction of the rectus femoris muscle

Tension produced by isometric contraction of the rectus femoris muscle for rapid knee extension was examined at different levels of force with five normal subjects, using an on-line method to measure the timing and the rate of development of tension. Tension began to rise about 50 msec, after onset of electromyographic activity of the rectus femoris muscle, increased most sharply at about 60 msec, after its rise, and attained maximum at about 100 msec. The rate of tension development was determined solely by the maximum tension from first 20 msec, up to 100 msec., while timing remained approximately constant regardless of the force. The result confirmed well a force-control hypothesis of maximal speed ballistic movement of a body segment that the motor centre controls the amplitude of force output when time to develop tension is invariant.

Two Components of Motor Time: The Tension Lag and the Tension-Developing Phase

Motor time (MT) of the rectus femoris muscle for knee extension under loading on the leg with different weights and latency of isometric tension from the onset of electromyographic activities of the muscle were examined in 7 normal men. MT was linearly related to weights-loaded, indicating that the rate of rapid development of tension was almost linear even in its early phase. MT without a load obtained by calculation using the regression equation and the estimated weight of the leg and foot coincided with latency of isometric tension. It is assumed that MT is composed of two consecutive phases, a tension-lag phase and a rapid tension-developing phase.

RHYTHMIC CONTROL OF A PUSH-PULL MOVEMENT

Rhythmic movement control was investigated in a ‘push-pull’ movement. The subject was asked to move a handle on the smooth rails forward (push) and backward (pull) alternatively between two plates and to synchronize each push and pull movement with periodic sound signals (1 to 5.8 Hz). All subjects synchronized one cycle of the push-pull movement accurately and steadily with two periods of signals over all input frequencies above 2 Hz. As for two components of the movement, i.e., the push and the pull, 9 out of 10 subjects (using the preferred hand) controlled each of them rhythmically so as to deviate equally from the signal towards the opposite directions, but 2.5 and 5 Hz were the exceptional regions at which the rhythmicity disappeared. These characteristics were fundamentally the same as those of finger tapping. It is concluded that the human alternating movement is controlled through the formation of specific rhythm and that this rhythm has intrinsic instabilities around 5, 2.5, … Hz.