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Titolo:
CATCHING A BALL - CONTRIBUTIONS OF INTRINSIC MUSCLE-STIFFNESS, REFLEXES, AND HIGHER-ORDER RESPONSES
Autore:
BENNETT DJ; GORASSINI M; PROCHAZKA A;
Indirizzi:
UNIV ALBERTA,DIV NEUROSCI EDMONTON T6G 2H7 AB CANADA UNIV ALBERTA,DIV NEUROSCI EDMONTON T6G 2H7 AB CANADA
Titolo Testata:
Canadian journal of physiology and pharmacology
fascicolo: 5, volume: 72, anno: 1994,
pagine: 525 - 534
SICI:
0008-4212(1994)72:5<525:CAB-CO>2.0.ZU;2-H
Fonte:
ISI
Lingua:
ENG
Soggetto:
SHORT-LATENCY REFLEXES; TRICEPS SURAE MUSCLES; HUMAN STRETCH REFLEX; MAMMALIAN MUSCLE; MOVEMENTS; JOINT; CONTRACTION; COMPONENTS; SINGLE; ARM;
Keywords:
REFLEXES; MUSCLE STIFFNESS; MOTOR CONTROL;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
29
Recensione:
Indirizzi per estratti:
Citazione:
D.J. Bennett et al., "CATCHING A BALL - CONTRIBUTIONS OF INTRINSIC MUSCLE-STIFFNESS, REFLEXES, AND HIGHER-ORDER RESPONSES", Canadian journal of physiology and pharmacology, 72(5), 1994, pp. 525-534

Abstract

In three sets of experiments in nine normal subjects and a patient with a percutaneous wrist stabilizing splint, we quantified the open-loop gain (OLG) of the stretch reflex acting about the elbow. The subjects exerted a steady mean flexing force and were instructed not to intervene (i.e., not to resist actively) when force or displacement perturbations were imposed on the forearm. The method was either to reconstruct transmission around the entire loop in a two-part experiment, or touse the attenuation of external perturbations in normal and electrically stimulated muscle to compute gain. Across all experiments, the mean magnitude of stretch reflex OLG was close to unity in the frequency range 1-2 Hz, and declined at higher frequencies, as required to ensure stability, given that the phase lag approached 180 degrees at 5 Hz. Inherent muscle stiffness was approximately equal to reflex stiffness. In functional terms, an OLG of 1 means that the yield caused by a force perturbation is approximately halved by reflex action (prevailing inherent muscle stiffness is doubled). Automatic scaling of reflex transmission at Ia/alpha-motoneuronal synapses ensures that the OLG remains close to unity as inherent stiffness increases. Trials in the patient with the wrist fixator gave similar results, indicating that the reflexes were proprioceptively mediated. In a fourth experiment in which the task was to catch a heavy ball, we compared the efficacy of inherent muscle stiffness and reflexes alone, with the subject's intentionalreactions, which included predictive and voluntary components of response. The latter were far more effective in maintaining the position of the hand after the ball was caught than inherent and reflex stiffnesses alone. We conclude that stability requirements limit the extent towhich stretch reflexes can augment inherent muscle stiffness. When inherent muscle stiffness is low, such as in our ball-catching task, thereflex stiffness is also low, and predictive and pre-programmed reactions predominate in load compensation, thus shifting the emphasis fromautomatic servo or equilibrium-point behaviour to higher order control.

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Documento generato il 27/01/21 alle ore 01:34:11