Coordinating two degrees of freedom during human arm movement: load and speed invariance of relative joint torques
G. L. Gottlieb, Q. Song, D. A. Hong and D. M. Corcos NeuroMuscular Research Center, Boston University, Massachussetts 02215, USA. 1. Eight subjects performed three series of pointing tasks with the unconstrained arm. Series one and two required subjects to move between two fixed targets as quickly a...
Gespeichert in:
Veröffentlicht in: | Journal of neurophysiology 1996-11, Vol.76 (5), p.3196-3206 |
---|---|
Hauptverfasser: | , , , |
Format: | Artikel |
Sprache: | eng |
Schlagworte: | |
Online-Zugang: | Volltext |
Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
Zusammenfassung: | G. L. Gottlieb, Q. Song, D. A. Hong and D. M. Corcos
NeuroMuscular Research Center, Boston University, Massachussetts 02215, USA.
1. Eight subjects performed three series of pointing tasks with the
unconstrained arm. Series one and two required subjects to move between two
fixed targets as quickly as possible with different weights attached to the
wrist. By specifying initial and final positions of the finger tip, the
first series was performed by flexion of both shoulder and elbow and the
second by shoulder flexion and elbow extension. The third series required
flexion at both joints, and subjects were instructed to vary movement
speed. We examined how variations in load or intended speed were associated
with changes in the amount and timing of the electromyographic (EMG)
activity and the net muscle torque production. 2. EMG and torque patterns
at the individual joints varied with load and speed according to most of
the same rules we have described for single-joint movements. 1) Movements
were produced by biphasic torque pulses and biphasic or triphasic EMG
bursts at both joints. 2) The accelerating impulse was proportional to the
load when the subject moved "as fast and accurately as possible" or to
speed if that was intentionally varied. 3) The area of the EMG bursts of
agonist muscles varied with the impulse. 4) The rates of rise of the net
muscle torques and of the EMG bursts were proportional to intended speed
and insensitive to inertial load. 5) The areas of the antagonist muscle EMG
bursts were proportional to intended movement speed but showed less
dependence on load, which is unlike what is observed during single-joint
movements. 3. Comparisons across joints showed that the impulse produced at
the shoulder was proportional to that produced at the elbow as both varied
together with load and speed. The torques at the two joints varied in close
synchrony, achieving maxima and going through zero almost simultaneously.
4. We hypothesize that "coordination" of the elbow and shoulder is by the
planning and generation of synchronized, biphasic muscle torque pulses that
remain in near linear proportionality to each other throughout most of the
movement. This linear synergy produces movements with the commonly observed
kinematic properties and that are preserved over changes in speed and load. |
---|---|
ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.1996.76.5.3196 |