This study, therefore, aimed to investigate the acute effects of WBV on the reflex (soleus H-reflex) and non-reflex (passive stiffness of MG muscle) components of spastic hypertonia in both the paretic and non-paretic limbs of individuals with chronic stroke. To measure passive muscle stiffness, ultrasound elastography, which has been shown to be a valid and reliable tool 16, would be used in this study. Its amplitude is a valuable parameter to quantify the hyperreflexia 15. An electrically evoked H-reflex, which bypasses the muscle spindles, may be advantageous in assessing the modulation of monosynaptic reflex activity 15.
A thorough mechanistic investigation into the physiological effects of WBV on spastic hypertonia may elucidate the potential benefits of this modality. However, there is a paucity of evidence regarding the effects of WBV on the reflex and non-reflex components of spastic hypertonia post-stroke 3. Thus, collectively, WBV may have the potential to modulate the passive mechanical properties of muscle 13, 14. Moreover, the repetitive mechanical stretching endured by muscles and tendons during the vibration may reduce soft tissue stiffness as indicated by the improved sit-and-reach performance previously observed in healthy populations 13. Evidence also suggested that for young adults, WBV could produce a training effect in muscle by increasing tissue oxygenation 6, blood perfusion 11, and intramuscular temperature 12. WBV has been shown to inhibit the Hoffman reflex (H-reflex) in healthy athletes and young adults 5, 6, 7, 8, 9, which is due to the presynaptic inhibition of Ia afferents 10, and/or the depletion of neurotransmitters within the presynaptic terminals 8. Whole-body vibration (WBV), a treatment modality involving the delivery of mechanical stimuli to the lower limbs via a vibration platform, has the potential to manage spastic hypertonia 3, 4. hyperreflexia) and a non-reflex component (e.g. Evidence has suggested that spastic hypertonia has both a reflex component (e.g. Although the primary origin of spasticity is impaired reflex function, changes in muscle mechanical properties also occur 2. Spastic hypertonia is common in leg extensors after stroke 1 which may impose negative effects on mobility and balance and compromise daily life activities 1, 2. No acute effect on passive muscle stiffness was observed. Based on our results, WBV had an acute effect on modulating spastic hypertonia dominated by hyperreflexia in people with chronic stroke and facilitating greater intramuscular blood perfusion. No significant change of the shear modulus in the MG muscle was observed, regardless of the testing condition. The vascular index of MG muscle was significantly increased only for the WBV condition, which lasted for 3 minutes and 5 minutes, respectively. The inhibition of H-reflex was sustained up to 4 minutes and 3 minutes on the paretic and non-paretic side, respectively. The results revealed a significant inhibition of the H/M ratio bilaterally for the WBV condition (absolute change on paretic side: 0.61 ± 0.35, p = 0.001 non-paretic side: 0.34 ± 0.23, p = 0.001), but not the control condition. We assessed the soleus H-reflex, shear modulus (ultrasound elastography) and vascular index (color power Doppler ultrasound) of the medial gastrocnemius (MG) muscle on either paretic or non-paretic side at baseline and every 1-min post-intervention up to 5 minutes.
Each participant underwent two testing conditions: static standing for 5 minutes with WBV (30 Hz, 1.5 mm) or no-vibration. Thirty-six people with chronic stroke (age: 61.4 ± 6.9 years) participated in this randomized controlled cross-over study.
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Full membership to the IDM is for researchers who are fully committed to conducting their research in the IDM, preferably accommodated in the IDM complex, for 5-year terms, which are renewable.This study aimed to investigate the acute effect of whole-body vibration (WBV) on the reflex and non-reflex components of spastic hypertonia and intramuscular blood perfusion among individuals with chronic stroke.
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