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Titolo:
Reflex and intrinsic changes induced by fatigue of human elbow extensor muscles
Autore:
Zhang, LQ; Rymer, WZ;
Indirizzi:
Rehabil Inst Chicago, Sensory Motor Performance Program, Chicago, IL 60611USA Rehabil Inst Chicago Chicago IL USA 60611 e Program, Chicago, IL 60611USA Northwestern Univ, Dept Phys Med & Rehabil, Chicago, IL 60611 USA Northwestern Univ Chicago IL USA 60611 d & Rehabil, Chicago, IL 60611 USA Northwestern Univ, Dept Orthoped Surg, Chicago, IL 60611 USA Northwestern Univ Chicago IL USA 60611 thoped Surg, Chicago, IL 60611 USA Northwestern Univ, Dept Biomed Engn, Chicago, IL 60611 USA Northwestern Univ Chicago IL USA 60611 Biomed Engn, Chicago, IL 60611 USA Northwestern Univ, Dept Physiol, Chicago, IL 60611 USA Northwestern Univ Chicago IL USA 60611 ept Physiol, Chicago, IL 60611 USA
Titolo Testata:
JOURNAL OF NEUROPHYSIOLOGY
fascicolo: 3, volume: 86, anno: 2001,
pagine: 1086 - 1094
SICI:
0022-3077(200109)86:3<1086:RAICIB>2.0.ZU;2-0
Fonte:
ISI
Lingua:
ENG
Soggetto:
MAXIMAL VOLUNTARY CONTRACTIONS; MOTONEURON FIRING RATES; TRICEPS SURAE MUSCLES; MUSCULAR FATIGUE; NEURAL COMPENSATION; FUSIMOTOR NEURONS; DISCHARGE RATE; FIBERS; STIMULATION; CAT;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Citazioni:
45
Recensione:
Indirizzi per estratti:
Indirizzo: Zhang, LQ Rehabil Inst Chicago, Sensory Motor Performance Program, Suite 1406,345 E Superior St, Chicago, IL 60611 USA Rehabil Inst Chicago Suite 1406,345 E Superior St Chicago IL USA 60611
Citazione:
L.Q. Zhang e W.Z. Rymer, "Reflex and intrinsic changes induced by fatigue of human elbow extensor muscles", J NEUROPHYS, 86(3), 2001, pp. 1086-1094

Abstract

Fatigue-induced changes in intrinsic and reflex properties of human elbow extensor muscles and the underlying mechanisms for fatigue compensation were investigated. The elbow joint was perturbed using small-amplitude and pseudorandom movement patterns while subjects maintained steady levels of meanjoint extension torque. Intrinsic and reflex properties were identified simultaneously using a nonlinear delay differential equation model. Intrinsicjoint properties were characterized by measures of joint stiffness, viscous damping, and limb inertia and reflex properties characterized by measuresof dynamic and static reflex gains. Fatigue was induced using 15 min of intermittent voluntary isometric (submaximal) exercise, and a rest period of 10 min was taken to allow the fatigued muscles to recover from acute fatigue effects. Identical experimental and data analysis procedures were used before and after fatigue. Our findings were that after fatigue, joint stiffness was significantly reduced at higher torque levels, presumably reflectingthe reduced force-generating. capacity of fatigued muscles. Conversely, joint viscosity was increased after fatigue potentially because of the reduced crossbridge detachment rate and prolonged relaxation associated with intracellular acidosis accompanying fatigue. Static stretch reflex gain decreased significantly at higher torque levels after fatigue, indicating that theisometric fatiguing exercise might be associated with a preferential change in properties of spindle chain fibers and bag, fibers. For matched pre- and postfatigue torque levels, dynamic reflexes contributed relatively more torque after fatigue, displaying hh,her dynamic reflex gains and larger dynamic electromyographic responses elicited by the controlled small-amplitude. position perturbations. These changes appear to counteract the fatigue-induced reductions in joint stiffness and static reflex gain. The compensatory responses could be partly due to the effects of increasing the number of active motoneurons innervating the fatiguing muscles. This shift in operating point gave rise to significant compensation for the. loss of contractileforce. The compensation could also be due to fusimotor adjustment, which could make the dynamic reflex gain much less sensitive to fatigue than intrinsic stiffness. In short, the reduced contribution from intrinsic stiffnessto joint torque was compensated by increased contribution from dynamic stretch reflexes after fatigue.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 20/09/20 alle ore 00:41:20