Ballistic flexion movements of the human thumb.

Abstract

SUMMARY1. In response to an auditory stimulus normal subjects made ballistic flexion movements of the top joint of the thumb against a lever attached to the spindle of a low-inertia electric motor.2. Electromyographic (e.m.g.) activity was recorded from pairs of fine wire electrodes inserted into flexor pollicis longus and extensor pollicis longus, respectively the sole flexor and extensor of the joint. 4. The e.m.g. activity initiating such movements was characterized by a 'triphasic' pattern of sequential bursts of activity in the agonist (flexor pollicis longus), then in the antagonist (extensor pollicis longus), and then in the agonist again.5. The duration of the first agonist and first antagonist bursts ranged from about 50 to 90 ms and there was no significant change of burst length in the different mechanical conditions. 6. In movements of differing angular distance, the rectified and integrated e.m.g. activity of the first agonist burst could be correlated with the distance moved. The rectified and integrated e.m.g. activity of the first antagonist burst could not be correlated with the distance moved.7. Responses of the muscles to perturbations either before or during the ballistic movements were studied. Current in the motor could be altered so to extend the thumb ('stretch'), to allow it to accelerate ('release'), or to prevent further movement (' halt').8. Suitably timed stretch increased the e.m.g. activity of the first agonist burst while release decreased it.9. There was a small response of the agonist to stretch or halt timed to act during the interval between the first two agonist bursts; the major response was an augmentation of the second agonist burst.10. Stretch, timed to act between the first two agonist bursts which released the antagonist, diminished the activity of the first antagonist burst while halt virtually eradicated it in all but one subject. Release, at this time, which stretched the antagonist, increased the activity of the first antagonist burst. M. HALLETT AND C. D. MARSDEN 11. It is concluded that the individual components of a ballistic movement are relatively fixed in duration and the amount of e.m.g. activity is altered within this time interval to produce the different forces required for fast movements of different amplitude.12. Both agonist and antagonist muscles remain under some feed-back control during the entire course of a ballistic movement, but the amount of influence of feed-back depends on the supraspinal command signal and the changes in the spindle during the course of the movement.

Rapid goal-directed elbow flexion movements: limitations of the speed control system due to neural constraints

“…This is true for the accelerating agonist activity, as well as for the decelerating antagonist activity (torque = moment of inertia x angular acceleration). As was observed in fastest voluntary goal-directed movements of the hand and forearm muscles (Freund and Biidingen 1978;Hallett and Marsden 1979), an increase of the amplitude in such movements is automatically combined with higher angular velocity and acceleration, thereby keeping the movement time constant (speed control system; Freund and Btidingen 1978). However, our investigations show that for elbow movements this speed control system is not as effective as in the distal muscles: the movement time is not kept constant at increasing movement amplitudes, although the movement velocity is enhanced.…”

“…In contrast to other investigations about goal-directed movements, the targets were presented as real targets in space and not displayed as bars on an oscilloscope (Hallett et al 1975;Hallett and Marsden 1979;Brown and Cooke 1981;Brown and Cooke 1984;Berardelli et al 1984).…”

“…However, now a large number of studies is available, which convincingly demonstrate that the triphasic EMG pattern is modifiable by unpredictable changes of peripheral inputs prior to and during the movements Adam et al 1976;Hallett and Marsden 1979;Cooke 1980;Mortimer et al 1981;Day and Marsden 1982;Day et al 1983). Furthermore, in contrast to the study of Hallett (1975), which focused on relatively small amplitude movements, it was recently demonstrated (Brown and Cooke 1984;Berardelli et al 1984) that the timing of the three-burst-pattern indeed could be modified by the movement amplitude alone.…”

The relation of integrated EMG of the triceps brachii to force in rapid elbow extension.

“…Recent studies have indicated that the duration of the first burst activity lasting within 100 msec in the agonist is not affected by mechanical perturbations imposed on the moving body segment either prior to or during the burst (Garland et al 1972;Hallett et al 1975), nor by velocity or force output of the movement (Hallett and Marsden 1979;Nagasaki et al 1983). These characteristics have been considered as clear evidence that the first burst activity of the agonist is preprogrammed by motor center without modification by sensory feedback.…”

“…Experimental investigation into the relation of the first burst activity to biomechanical variables of the movement would provide evidence for the question. Hallett and Marsden (1979), studying rapid flexion of the interpharangeal joint of the thumb, demonstrated linear correlation between the rectified and integrated EMG (iEMG) of the first burst activity and maximal velocity of the movement, but they did not examine the force output. In contraction of the biceps brachii muscle for elbow flexion with or without Received April 15, 1985; accepted for publication May 10, 1986.…”