Muscle activity and vibration transmissibility during whole-body vibration in chronic stroke.

PURPOSE: This study aimed to investigate the influence of whole-body vibration (WBV) frequency, amplitude, and body posture on lower limb muscle activation among people with chronic stroke, and whether the EMG response to vibration stimulus differed between paretic and non-paretic side. The relationship between muscle activation and WBV transmission was also examined.

METHOD: Thirty-two participants with chronic stroke performed three different exercises on the WBV platform with different vibration conditions (frequency: 20 Hz, 30 Hz, 40 Hz; amplitude: 0.8 mm, 1.5 mm), or without vibration. Muscle activity in bilateral vastus medialis (VM), medial hamstrings (MH), tibialis anterior (TA), and medial gastrocnemius (MG) was measured by surface electromyography. Acceleration at the platform and bilateral hips and knees was measured by tri-axial accelerometers.

RESULTS: Significantly greater muscle activity was observed in the bilateral MG (P < 0.001), TA (P < 0.001), and MH (P < 0.001), but not VM, compared with the same exercises without WBV. WBV with higher amplitude or higher frequency led to greater augmentation of muscle activation (P < 0.05). Body posture significantly affected leg muscle activation (P < 0.001). WBV-induced muscle activation was largely similar between paretic and non-paretic sides, except the TA. Greater WBV-induced leg muscle activation was associated with lower WBV transmissibility measured at the more proximal joints (P < 0.05).

CONCLUSION: Adding WBV to exercise significantly increased muscle activation in the MG, TA, and MH on both the paretic and non-paretic sides of chronic stroke survivors, and the increase was dependent on the WBV amplitude, frequency, and body posture.