Effect of whole-body vibration on lower-limb EMG activity in subjects with and without spinal cord injury

Abstract

Objective: Traumatic spinal cord injury (SCI) results in substantial reductions in lower extremity muscle mass and bone mineral density below the level of the lesion. Whole-body vibration (WBV) has been proposed as a means of counteracting or treating musculoskeletal degradation after chronic motor complete SCI. To ascertain how WBV might be used to augment muscle and bone mass, we investigated whether WBV could evoke lower extremity electromyography (EMG) activity in able-bodied individuals and individuals with SCI, and which vibration parameters produced the largest magnitude of effect.

Methods: Ten male subjects participated in the study, six able-bodied and four with chronic SCI. Two different manufacturers' vibration platforms (WAVE(®) and Juvent™) were evaluated. The effects of vibration amplitude (0.2, 0.6 or 1.2 mm), vibration frequency (25, 35, or 45 Hz), and subject posture (knee angle of 140°, 160°, or 180°) on lower extremity EMG activation were determined (not all combinations of parameters were possible on both platforms). A novel signal processing technique was proposed to estimate the power of the EMG waveform while minimizing interference and artifacts from the plate vibration.

Results: WBV can elicit EMG activity among subjects with chronic SCI, if appropriate vibration parameters are employed. The amplitude of vibration had the greatest influence on EMG activation, while the frequency of vibration had lesser but statistically significant impact on the measured lower extremity EMG activity.

Conclusion: These findings suggest that WBV with appropriate parameters may constitute a promising intervention to treat musculoskeletal degradation after chronic SCI.

Keywords: Electromyography; Musculoskeletal health; Osteoporosis; Spinal cord injury; Whole-body vibration.

Figures

Figure 1

The WAVE® vibration platform and the standing frame (experimental setup). Reproduced from Alizadeh-Meghrazi et al.32

Figure 2

Mean + standard deviation of EMG power for each muscle in AB individuals using the WAVE® platform, as a function of the vibration and posture parameters (frequency of 25, 35, or 45 Hz; amplitude of 0.6 mm or 1.2; knee angle of 140°, 160°, or 180°). Activation levels recorded during passive sitting are provided (red dotted line) for comparison with the vibration-induced activity. A single asterisk (*) denotes WBV-induced activity that is significantly greater than sitting levels, whereas a double asterisk denotes induced activity that is significantly greater than active standing levels. VL, vastus lateralis; GM, gastrocnemius medialis; RF, rectus femoris; SO, soleus; TA, tibialis anterior.

Figure 3

Mean + standard deviation of EMG power for each muscle in individuals with SCI using the WAVE® platform, as a function of the vibration and posture parameters (frequency of 25, 35, or 45 Hz; amplitude of 0.6 or 1.2 mm; knee angle of 140° or 160°). Activation levels recorded during passive sitting are provided (red dotted line) for comparison with the vibration-induced activity. An asterisk (*) denotes WBV-induced activity that is significantly greater than sitting levels. VL, vastus lateralis; GM, gastrocnemius medialis; RF, rectus femoris; SO, soleus; TA, tibialis anterior.

Figure 4

Mean + standard deviation of EMG power for each muscle in AB individuals using the Juvent™ platform, as a function of the vibration and posture parameters (frequency of 25, 35, or 45 Hz; knee angle of 140°, 160°, 180°; amplitude was 0.2 mm in all cases). Activation levels recorded during passive sitting are provided (red dotted line) for comparison with the vibration-induced activity. An asterisk (*) denotes WBV-induced activity that is significantly greater than sitting levels. VL, vastus lateralis; GM, gastrocnemius medialis; RF, rectus femoris; SO, soleus; TA, tibialis anterior.

Figure 5

Mean + standard deviation of EMG power for each muscle in individuals with SCI using the Juvent™ platform, as a function of the vibration and posture parameters (frequency of 25, 35, or 45 Hz; knee angle of 140°, 160°, 180°; amplitude was 0.2 mm in all cases). Activation levels recorded during passive sitting are provided (red dotted line) for comparison with the vibration-induced activity. An asterisk (*) denotes WBV-induced activity that is significantly greater than sitting levels. VL, vastus lateralis; GM, gastrocnemius medialis; RF, rectus femoris; SO, soleus; TA, tibialis anterior.