Effects of Vibration Intensity, Exercise, and Motor Impairment on Leg Muscle Activity Induced by Whole-Body Vibration in People With Stroke

Lin-Rong Liao; Gabriel Y.F. Ng; Alice Y.M. Jones; Raymond C.K. Chung; Marco Y.C. Pang

doi:10.2522/ptj.20140507

Figures

Figure 1.

Exercise protocol: (A) upright standing position—standing with feet placed apart at shoulder width and knees slightly flexed at about 10° and holding for 10 seconds; (B) semi-squat position—standing with feet placed apart at shoulder width and knee flexed at 30° and holding for 10 seconds; (C) deep-squat position—standing with feet placed apart at shoulder width and knees flexed to 90° and holding for 10 seconds; (D) weight-shifted-forward position—starting position same as in upright standing exercise (exercise A), then leaning body weight forward (right) as much as possible and raising heels up and holding for 10 seconds; (E) weight-shifted-backward position—starting position same as in upright standing exercise (exercise A), then leaning body weight backward as much as possible and raising forefoot and holding for 10 seconds; (F) weight-shifted-to-the-side position—starting position same as in upright standing exercise (exercise A), then shifting body weight onto one leg as far as possible and holding for 10 seconds and repeating on the other side; (G) forward lunge position—standing in a forward lunge position with the paretic leg placed in front of the nonparetic leg and flexed at 10°, then leaning forward and shifting body weight onto the paretic leg as much as possible with knee flexed at 30° and holding for 10 seconds, then switching the positions of the 2 legs with the nonparetic leg placed in front of the paretic leg; (H) single-leg-standing position—standing on the paretic leg with knee flexed at 10° and holding for 10 seconds, then repeating on the nonparetic side.

Figure 2.

Study flowchart. A total of 36 people with stroke completed all measurements. WBV=whole-body vibration.

Figure 3.

Trend analysis: illustration of the effect of whole-body vibration (WBV) intensity. The relationship between normalized electromyography root mean square (EMG_rms) and WBV intensity is shown for (A) paretic tibialis anterior muscle (TA), (B) nonparetic TA, (C) paretic biceps femoris muscle (BF), and (D) nonparetic BF. Each data point represents the mean value of the normalized EMG_rms value for a given exercise at a particular WBV intensity. The error bar represents 1 standard error of the mean. For each exercise, the 3 data points were best fitted with a logarithmic curve. The thick purple line represents the trend after pooling the data of all 8 exercises. As it is impossible to fit the data with a logarithmic curve if one of the WBV intensities is 0g, a factor of 0.001g was added to yield WBV intensities of 0.001g, 0.961g, and 1.611g, respectively. Eight different static exercises were examined in each WBV condition: upright standing (ST), semi-squat (SSq), deep squat (DSq), weight-shifted-forward (FWS), weight-shifted-backward (BWS), weight-shifted-to-the-side (WSTS), forward lunge (FL), and single-leg-standing (SLS). %MVC=percent maximal voluntary contraction.

Figure 4.

Normalized electromyography (EMG) magnitude under different whole-body vibration exercise conditions. The normalized electromyography root mean square (EMG_rms) value of (A) paretic tibialis muscle (TA), (B) nonparetic TA, (C) paretic biceps femoris muscle (BF), and (D) nonparetic BF in each test condition is expressed as percent maximal voluntary contraction (%MVC). The white triangles (Δ), gray squares (), and black diamonds (♦) represent the mean normalized EMG_rms values recorded in the high-intensity WBV, low-intensity WBV, and no-WBV conditions, respectively. The error bars represent 1 standard error of the mean. Eight different static exercises were examined in each WBV condition: upright standing (ST), semi-squat (SSq), deep squat (DSq), weight-shifted-forward (FWS), weight-shifted-backward (BWS), weight-shifted-to-the-side (WSTS), forward lunge (FL), and single-leg-standing (SLS). Application of WBV resulted in an overall significant increase in normalized EMG_rms of the TA and BF on both sides. *Significant difference between the control condition (no WBV) and low-intensity WBV condition. †Significant difference between the control condition and high–intensity WBV protocol. ^#Significant difference between the low-intensity and high-intensity WBV protocols.

Tables

Table 1.

Characteristics of the Participants (N=36)^{^a}

↵^a Mean±SD presented for continuous variables. CMSA=Chedoke–McMaster Stroke Assessment, EMG=electromyography, MAS=Modified Ashworth Scale, MVC=maximal voluntary contraction, EMG_rms=electromyography root mean square, BF=biceps femoris muscle, TA=tibialis anterior muscle.
^b Modified Ashworth Scale is a 6-point ordinal scale. The category 1+ was converted to 1.5 for statistical analysis.

Table 2.

Effect of WBV Intensity on Normalized EMG_rms Values^{^a}

↵^a WBV=whole-body vibration, EMG_rms=electromyography root mean square, CI=confidence interval, TA=tibialis anterior, BF=biceps femoris. *Statistically significant (P<.05).
^b Greenhouse-Geisser epsilon adjustment was used to generate the F score, degrees of freedom (df), and P values due to violation of the sphericity assumption.
^c Electromyography magnitude expressed as percent maximal voluntary contraction.
^d The P values for the contrast analysis are Bonferroni corrected values.