TY - JOUR
T1 - Short- and long-latency reflex responses during different motor tasks in elbow flexor muscles
AU - Nakazawa, Kimitaka
AU - Yamamoto, Shin Ichiroh
AU - Yano, Hideo
PY - 1997
Y1 - 1997
N2 - Stretch reflex responses in three elbow flexor muscles - the brachioradialis and the short and long heads of the biceps brachii - were studied during different motor tasks. The motor tasks were iso-velocity (8 deg/s) elbow flexion movements in which the muscles performed shortening or lengthening contractions, or were isometric contractions. Care was taken to maintain constant background electromyographic (EMG) activity in the brachoradialis muscle at a 50-deg elbow angle across the tasks by changing the magnitude of the initial load. During each task, mechanical perturbations (duration 170 ms) were applied at pseudorandom intervals when the elbow angle was 50 deg. The magnitude of the perturbation was varied across tasks in order to induce an elbow extension velocity of 80 deg/s over the first 50 ms after the onset of perturbation. The stretch reflex EMG responses in all muscles varied across the three tasks, despite a constant EMG level and similar perturbation-induced angular velocity in the direction of elbow extension. In particular, both the short- and long-latency reflex EMG components were reduced during the lengthening contractions. Further, the task-dependent variations in the early (M2) and the late (M3) components of the long-latency reflex were different, i.e., the magnitude of M3 was considerably enhanced during the shortening task as compared with that of M2. These findings suggest that central modification was responsible for the task-dependent modulation of late EMG responses.
AB - Stretch reflex responses in three elbow flexor muscles - the brachioradialis and the short and long heads of the biceps brachii - were studied during different motor tasks. The motor tasks were iso-velocity (8 deg/s) elbow flexion movements in which the muscles performed shortening or lengthening contractions, or were isometric contractions. Care was taken to maintain constant background electromyographic (EMG) activity in the brachoradialis muscle at a 50-deg elbow angle across the tasks by changing the magnitude of the initial load. During each task, mechanical perturbations (duration 170 ms) were applied at pseudorandom intervals when the elbow angle was 50 deg. The magnitude of the perturbation was varied across tasks in order to induce an elbow extension velocity of 80 deg/s over the first 50 ms after the onset of perturbation. The stretch reflex EMG responses in all muscles varied across the three tasks, despite a constant EMG level and similar perturbation-induced angular velocity in the direction of elbow extension. In particular, both the short- and long-latency reflex EMG components were reduced during the lengthening contractions. Further, the task-dependent variations in the early (M2) and the late (M3) components of the long-latency reflex were different, i.e., the magnitude of M3 was considerably enhanced during the shortening task as compared with that of M2. These findings suggest that central modification was responsible for the task-dependent modulation of late EMG responses.
KW - Elbow
KW - Human
KW - Long-latency reflex
KW - Reflex and voluntary control of movement
KW - Shortening and lengthening contractions
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U2 - 10.1007/PL00005740
DO - 10.1007/PL00005740
M3 - Article
C2 - 9305811
AN - SCOPUS:0030798001
VL - 116
SP - 20
EP - 28
JO - Experimental Brain Research
JF - Experimental Brain Research
SN - 0014-4819
IS - 1
ER -