Author/Editor		Gollhofer, A; Schoepp, A; Rapp, W; Strojnik, V
Title		Changes in reflex excitability following isometric contraction in humans
Type		članek
Source		Eur J Appl Physiol
Vol. and No.		Letnik 77
Publication year		1998
Volume		str. 89-97
Language		eng
Abstract		Enhancement of muscle stretch following isometric contraction has been thought to occur as a result of inhibitory reflex mechanisms. Experiments with electrical stimulation (H-reflex) have demonstrated maximal H-reflex suppression during force relaxation followed by gradual recovery over the following 20 s. There has been considerable speculation as to whether electrical and mechanical stimulation elicit similar response behaviour. The present study examined postisometric reflex modulation following both stimulation modalities. In ten subjects dorsiflexion stimuli varying in speed and amplitude were applied after 30% and 60% maximal voluntary contraction (MVC). Modulation of the mechanically and electrically evoked responses following isometric plantarflexion was investigated. Reflex responses following both stimulation modalities were depressed during the course of force relaxation. A rather fast recovery was observed inmechanical stimulation. Postisometric response modulation was neither altered by the amount of isometric plantarflexion, nor by the amplitude of the applied stretch stimulus. With increasing velocity of the applied dorsiflexion, however, the shape of the reflex modulation persisted, but the magnitude of the responses was significantly enhanced. In electrical stimulation, however, recovery was delayed. It is suggested that postisometric reflex modulation is due to presynaptic inhibition. Moreover, possible peripheral mechanisms resulting from alpha-gamma-coactivation may also affect the stretch receptor itself because of inherent stiffiness properties. The latter possibility particularly would explain the difference sbetween mechanical and electrical stimulus modalities.(Abstract truncated at 2000characters.)
Descriptors		ISOMETRIC CONTRACTION ELECTRIC STIMULATION REFLEX, STRETCH MUSCLE CONTRACTION PHYSICAL STIMULATION ADULT LEG REFLEX, MONOSYNAPTIC ERGOMETRY ELECTROMYOGRAPHY