Comparison of monosynaptic tendon reflexes during preparation for ballistic or ramp movement.

Mechanism which underlie preparation for movement were studied in man using the method of 'monosynaptic tendon reflexes' during the preparatory period (PP) preceding the execution of ramp or ballistic tracking movements. Reflex reactivity is more important during the whole of the PP to a ramp rather than a ballistic movement; the increasing facilitation preceding the execution signal is greater and occurs earlier for the ramp than for the ballistic movement. These results were observed for 'fast' or 'slow' subjects in a reaction time task, but were more marked for the latter. On the one hand, preparation for movement is represented at the spinal level by a competition between activating influences, which allows for the speeding up of peripheral execution of central control, and inhibitory influences brought into play both by the need to suppress the movement until the execution signal and by the isolation of motor structures from postural proprioceptive servo-mechanisms. On the other hand, this preparation can imply a control of the level of activity in proprioceptive fusorial afferent pathways which depends on whether the movement to be executed is open-loop (ballistic) or closed (ramp). Comparison between the results obtained from fast and slow subjects underlines the importance of an active inhibitory process in spinal structures which would accompany temporal adjustment.