Prolonged muscle vibration increases stretch reflex amplitude, motor unit discharge rate, and force fluctuations in a hand muscle

Abstract

The purpose of this study was to compare the influence of prolonged vibration of a hand muscle on the amplitude of the stretch reflex, motor unit discharge rate, and force fluctuations during steady, submaximal contractions. Thirty-two young adults performed 10 isometric contractions at a constant force (5.0 +/- 2.3% of maximal force) with the first dorsal interosseus muscle. Each contraction was held steady for 10 s, and then stretch reflexes were evoked. Subsequently, 20 subjects had vibration applied to the relaxed muscle for 30 min, and 12 subjects received no vibration. The muscle vibration induced a tonic vibration reflex. The intervention (vibration or no vibration) was followed by 2 sets of 10 constant-force contractions with applied stretches (After and Recovery trials). The mean electromyogram amplitude of the short-latency component of the stretch reflex increased by 33% during the After trials (P < 0.01) and by 38% during the Recovery trials (P < 0.01). The standard deviation of force during the steady contractions increased by 21% during the After trials (P < 0.05) and by 28% during the Recovery trials (P < 0.01). The discharge rate of motor units increased from 10.3 +/- 2.7 pulses/s (pps) before vibration to 12.2 +/- 3.1 pps (P < 0.01) during the After trials and to 11.9 +/- 2.6 pps during the Recovery trials (P < 0.01). There was no change in force fluctuations or stretch reflex magnitude for the subjects in the Control group. The results indicate that prolonged vibration increased the short-latency component of the stretch reflex, the discharge rate of motor units, and the fluctuations in force during contractions by a hand muscle. These adjustments were necessary to achieve the target force due to the vibration-induced decrease in the force capacity of the muscle.

Experimental muscle pain increases normalized variability of multidirectional forces during isometric contractions

“…Second, it has been shown that hypertonic saline excites group III and IV afferent fibres (Kumazawa and Mizumura 1977), which converge on common interneurons in pathways from group Ia and Ib afferents (muscle spindles and Golgi tendon organs) (Schomburg et al 1999). Inhibitory pathways converging into group Ia afferents decrease excitatory input to alpha-motoneurons, hence modulating force fluctuations (Yoshitake et al 2004;Shinohara et al 2005). In addition, spatial facilitation between group III and IV muscle afferents and Ib afferents may modulate the sensitivity of muscle tension control by decreased reflex sensitivity in agonist muscles and increased reflex sensitivity in antagonist muscles (Graven-Nielsen et al 2002), modifying the ability of the central nervous system to interpret proprioceptive information needed to precisely control force or position of the limbs (Wessberg and Vallbo 1995).…”

Prolonged Vibration of the Biceps Brachii Tendon Reduces Time to Failure When Maintaining Arm Position With a Submaximal Load

“…Vibration simultaneously influences both Ia function (Schieppati et al 2001) and force fluctuations (Cresswell and Löscher 2000;Shinohara et al 2005;Yoshitake et al 2004). Because the net muscle torque and limb position remained constant across the three vibration conditions, comparison of the SD of acceleration provides a measure of the relative mechanical work performed during the three conditions.…”

“…Because prolonged vibration alters the magnitude of the force fluctuations during an isometric contraction (Cresswell and Löscher 2000;Shinohara et al 2005;Yoshitake et al 2004) and thereby the amount of mechanical work performed during the task, a secondary purpose was to quantify the extent to which differences in limb acceleration induced by three levels of vibration contributed to changes in the time to failure across conditions. It was expected that different levels of vibration would produce a larger range of changes in limb acceleration to allow examination of the role of mechanical work in contributing to differences in the time to failure of the fatiguing contractions.…”

Visuomotor contribution to force variability in the plantarflexor and dorsiflexor muscles

“…In addition to variability related to the membrane noise properties of motor neurons (Calvin & Stevens, 1968;Powers & Binder, 2000), the discharge behavior of motor units is influenced by the supraspinal (voluntary command), spinal, and reflex inputs they receive (Parkis, Feldman, Robinson, & Funk, 2003;Salenius, Portin, Kajola, Salmelin, & Hari, 1997). As an example, when muscle spindle afferent feedback is disturbed by long term vibration, the variability of motor output during steady contractions is altered (Shinohara, Moritz, Pascoe, & Enoka, 2005;Yoshitake, Shinohara, Kouzaki, & Fukunaga, 2004). The supraspinal descending command can be modulated by visual information.…”