Muscle Activation Patterns During Two Types of Voluntary Single-Joint Movement

Abstract

We examined the systematic variations in the EMG patterns during two types of single joint elbow movements. These patterns may be interpreted as exhibiting rules by which the CNS controls movement parameters. Normal human subjects performed two series of fast elbow flexion movements of 20-100 degrees in a horizontal plane manipulandum. The first series consisted of pointing movements (PMs) from an initial position to a target; the second series consisted of reversal movements (RMs) to the same targets with an immediate return to the starting position. Both series showed kinematic and electromyographic (EMG) patterns that followed our previously described speed-insensitive strategy for controlling movement distance. Kinematic patterns of PMs and RMs were identical to about the time of peak PM deceleration. Agonist EMG bursts were also initially the same, but RM bursts ended abruptly in a silent period, whereas PM bursts declined more gradually. Antagonist EMG bursts of RMs were later than those of PMs but were not larger, contrary to our prior expectation and despite the larger net extension torque during RMs. The increase in net RM extension-directed torque that takes the limb back to its initial position appears to be a consequence of reduced flexor muscle torque rather than increased extensor muscle torque. We propose that rules for movement control may be similar for different kinds of movements as long as they are functionally sufficient for the task. However, even in a single-joint movement paradigm, physics alone, that is, the knowledge of net muscle torque and limb kinematics, is not adequate to fully predict those rules or the muscle activation patterns they produce. These must be discovered by experiment. The simplest expression of such rules may not be in terms of torque or kinematic variables but rather explicitly in terms of muscle activation patterns.

Control of velocity and position in single joint movements

“…Our current findings integrate and expand the pulse-step model of Ghez and colleagues (Ghez, 1979;Gordon & Ghez, 1984, 1987a with the model of Gottlieb and colleagues Gottlieb, 1996Gottlieb, , 1998Gottlieb et al, 1989Gottlieb et al, , 1990Gottlieb et al, , 1995Gottlieb et al, , 1996. Our findings provide support for the idea that during targeted movement tasks, pulse-height mechanisms specify movement speed, whereas pulse-width mechanisms appear to be adapted for modulation of final limb position.…”

“…Although the terminology used by Gottlieb and colleagues Gottlieb, 1996Gottlieb, , 1998Gottlieb, Chen, & Corcos, 1995, 1996Gottlieb et al, 1989;Gottlieb, Corcos, Agarwal, & Latash, 1990) was different than that of the Ghez group, the control models proposed by both groups were quite similar to one another. Both described a pulsatile output that can be modulated in both amplitude and duration.…”

Muscular activation patterns in swimmers with asymptomatic shoulder joint instability

“…The integrated values of the agonist ( EMG ag ) and antagonist ( EMG antag ) muscles, based on their velocity profiles, were used to evaluate the magnitude and duration of muscle activity observed during the movement. As was demonstrated by Gottlieb et al [10] and in other studies [12,15], the EMG 30 during fast movements is independent of movement distance. However, EMG magnitudes ( EMG ag and EMG antag ) increase with an increase in target distance [16].…”

Neuromechanics of muscle synergies for posture and movement

“…In most natural behaviors, task-level goals can be equivalently achieved with different kinetic or kinematic strategies [51][52][53], which can themselves be equivalently achieved with different spatial and temporal patterns of muscle activation [54•, 55,56]. Therefore, biomechanical models do not uniquely determine muscle activation patterns, nor do they predict muscle synergies, but rather they delineate the large "solution space" afforded by the musculoskeletal system for task performance.…”