Reflex responses to local soleus muscle vibration

Publikation: Beitrag in Buch/Bericht/KonferenzbandKonferenzbeitrag - Abstract in KonferenzbandForschungBegutachtung


Vibration is a powerful tool to activate muscle receptors. High-frequency vibrations are used to preferentially stimulate spindle primary endings [1,2] and to elicit the tonic vibration reflex [3,4]. Recently, the use of local vibration has emerged in a broad range of training [5,6] and rehabilitation settings [7]. There is increasing evidence that acute local vibratory stimulation can improve joint range of motion in both healthy [8,9] and spastic populations [10]. At the same time, prolonged vibratory stimulation has been shown to decrease the neuro-muscular output of the vibrated muscle [11,12,13]. Although the underlying mechanisms have not been fully understood, a decline in muscle force as a result of intrafusal muscle fatigue can lead to a decreased afferent feedback with subsequent disfacilitation of α-motoneurons [14,15]. This can lead to a down-regulation of muscle tone as well as a decline in the motor output of the receptor-bearing muscle. The aim of this work was to assess if vibration induced acute improvement in muscle flexibility and attenuation in maximum force production capacities can be explained by intrafusal muscle fatigue. Stretch reflexes were evoked in the quiescent soleus muscle in order to investigate the effect of the intervention on the intrafusal myofibril stiffness [16]. On the other side, stretch reflexes were evoked in the active soleus (20% MVT) muscle in order to investigate the effect of the vibration on the dynamic reflex gain (i.e. activity of γ-motoneuron) [17]. Objectives: to investigate the acute effects of local vibration on the short-latency stretch reflexes (SLR) of the soleus muscle. to investigate the acute effects of local vibration on the parameters of the H-reflex and M-wave recruitment curves. Hypothesis: Prolonged vibratory stimulation will induce intrafusal muscle fatigue, which will be reflected as a decrease in the myoelectric amplitudes of the SLRs elicited in both active and passive conditions. No change on dynamic reflex gain was expected to occur as a result of prolonged vibration. Subjects: Twelve healthy subjects (age 21.9 ± 2.2 years; height 1.78 ± 0.07 m; body mass 70.0 ± 11.7 kg) EMG: soleus and tibialis ant. muscles (sampling frequency: 5 kHz) Stretch reflex: passive and active (20% MVT) soleus muscle - preprogrammed motor-driven dorsiflexion movement (α = 28,000°/s²; ω = 340°/s; θ = 8°) Electrical nerve stimulation: posterior tibial nerve – unipolar stimulation technique – square pulse stimulus of 1ms - intra-stimulus interval ≥ 10sec H-Reflex and M-Wave: electromyographically silent soleus muscle Vibration: custom-made vibration device - five selected points on the soleus muscle (f = 150Hz; a = 1.6g; A(p-t-p) = 35μm per vibration unit) Procedure: measurements have been made before applying the vibration (pretreatment) – directly after initiation of vibration (short-term effects) – after 30min of sustained vibration (prolonged effects) and 10min after the termination of vibration (aftereffects). HMAX: The mean value of HMAX decreased significantly directly after applying the vibration (p = .007) and remained almost at the same level during the prolonged vibration (p < .001), while recovered to baseline in about 10 min after the end of the vibration (p = 1.00) (Fig. 6A). MMAX: The mean value of MMAX was significantly lower during the prolonged condition as compared to the aftereffects condition (p = .001), while being markedly lower than under pretreatment and short-term conditions (p = .059 and .083, respectively) (Fig. 6B). HSLPA: There was no statistically significant differences in the mean values of the maximum slope of the ascending limb of the H-reflex recruitment curve during the test conditions (p = .132 )(Fig. 6C). HSLPD: The mean value of the maximum slope of the descending limb of the H-reflex recruitment curve was significantly lower in the prolonged condition than in pretreatment (p = .016) and aftereffects conditions (p < .001). The mean value of HSLPD was also significantly lower in the short-term condition than in the aftereffects condition (p = .038) (Fig. 6D). SLR: There was no statistically significant main effect of treatment on peak-to-peak amplitude of the SLR (p = .346), while muscle activation had a significant effect (p = .025). The mean value of the SLR amplitude was significantly higher in the active conditions as compared to the passive conditions. There was no statistically significant interaction between the two factors (p = .353). It seems unlikely that prolonged vibration has induced intrafusal muscle fatigue, as measured by the SLRs. Though, both active and passive SLRs showed a great intra-individual variability during all test conditions which may be attributed to inherent variations in the mechanically-induced afferent volleys and/or methodological factors. The analysis of the ascending limb of the H-reflex recruitment curve demonstrated a strong negative correlation between the mean percentage decrease in H-reflex amplitudes after the vibration and the current intensity (r = -.985, p < .001). Since moto-neurons are recruited in the H-reflex from smallest to largest with increasing current intensities [24,25], the finding of this study suggests differential effects of presynaptic inhibition on alpha-motoneurons with the smallest motoneurons being more affected than the largest ones. MMAX amplitude decreased gradually over the duration of vibratory stimulation and recovered significantly after about 10 min from the end of the vibration. The depression of the MMAX after prolonged vibration may be related to neuromuscular transmission failure and/or reduced sarcolemmal excitability. Vibration-induced activation of stretch-activated ion channels (SACs) is one of the candidate mechanisms, which can explain some of the adaptive responses associated with chronic exposure to local vibration. The myoelectric amplitudes of SLRs of the soleus muscle were higher during muscle activation than during passive conditions. The increase in SLR responses during muscle activation can be attributed to increased spindle dynamic sensitivity due to α-γ-coactivation [17], decreased presynaptic inhibition [18] and/or improved transmission of stretch stimulus to stretch receptors [26]. The findings also suggest that the utilized vibration parameters have no effect on the electrical thresholds of neither the afferent nor efferent fibers. Spindle feedback plays an important role in reflexive neuromuscular control, functional joint stability, muscle tone, postural control, kinesthesia and force-generating capacity [14, 18-23]. 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TitelISBS 2017 : 35th Conference of the International Society of Biomechanics in Sports, Cologne, Germany, June 14-18, 2017
Herausgeber (Verlag)International Society of Biomechanics in Sports
PublikationsstatusVeröffentlicht - 07.2017
VeranstaltungConference of the International Society of Biomechanics in Sports (ISBS) - Köln, Deutschland
Dauer: 14.06.201718.06.2017
Konferenznummer: 35


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