Acute effects of stochastic resonance whole body vibration

AIM: To investigate the acute effects of stochastic resonance whole body vibration(SR-WBV) training to identify possible explanations for preventive effects against musculoskeletal disorders.METHODS: Twenty-three healthy, female students participated in this quasi-experimental pilot study. Acute physiological and psychological effects of SR-WBV training were examined using electromyography of descending trapezius(TD) muscle, heart rate variability(HRV), different skin parameters(temperature, redness and blood flow) and self-report questionnaires. All subjects conducted a sham SR-WBV training at a low intensity(2 Hz with noise level 0) and a verum SR-WBV training at a higher intensity(6 Hz with noise level 4). They were tested before, during and after the training. Conclusions were drawn on the basis of analysis of variance.RESULTS: Twenty-three healthy, female students participated in this study(age = 22.4 ± 2.1 years; body mass index = 21.6 ± 2.2 kg/m2). Muscular activity of the TD and energy expenditure rose during verum SRWBV compared to baseline and sham SR-WBV(all P < 0.05). Muscular relaxation after verum SR-WBV was higher than at baseline and after sham SR-WBV(all P < 0.05). During verum SR-WBV the levels of HRV were similar to those observed during sham SR-WBV. The same applies for most of the skin characteristics, while microcirculation of the skin of the middle back was higher during verum compared to sham SR-WBV(P < 0.001). Skin redness showed significant changes over the three measurement points only in the middle back area(P = 0.022). There was a significant rise from baseline to verum SR-WBV(0.86 ± 0.25 perfusion units; P = 0.008). The self-reported chronic pain grade indicators of pain, stiffness, well-being, and muscle relaxation showed a mixed pattern across conditions. Muscle and joint stiffness(P = 0.018) and muscular relaxation did significantly change from baseline to different conditions of SR-WBV(P < 0.001). Moreover, muscle relaxation after verum SR-WBV was higher than after sham SR-WBV(P < 0.05).CONCLUSION: Verum SR-WBV stimulated musculoskeletal activity in young healthy individuals while cardiovascular activation was low. Training of musculoskeletal capacity and immediate increase in musculoskeletal relaxation are potential mediators of pain reduction in preventive trials.

Acute effects of partial-body vibration in sitting position

AIM To investigate the acute effects of sinusoidal and stochastic resonance partial-body vibration in sitting position, including muscle activity, heart rate variability, balance and flexibility.METHODS Fifty healthy participants were assigned randomly to two training conditions: A sinusoidal partial-body vibration(SIN, 8 Hz) or a stochastic resonance partial-body vibration(STOCH, 8 ± 2 Hz). For baseline assessment participants sat on the vibration platform without vibration. Both training conditions consisted of five series of a one-minute vibration training and a one-minutebreak between them. In this experimental study surface electromyography(EMG) of the erector spinae(ES), one of the back muscles, and heart rate variability(HRV) was measured at baseline and during training. Balance and flexibility were assessed at baseline and immediately after training. Balance was measured with the modified star excursion balance test(mS EBT) and flexibility was assessed through the modified fingertip-to-floor method(mF TF).RESULTS Paired sample t-test showed a significant increase in balance that was restricted to STOCH(t =-2.22, P = 0.018; SIN: t =-0.09, P = 0.466). An increase in flexibility was also restricted to STOCH(t = 2.65, P = 0.007; SIN: t = 1.41, P = 0.086). There was no significant change of muscle activity in the ES-EMG in STOCH or SIN conditions. In both training conditions, HRV decreased significantly, but remained in a low-load range(STOCH: t = 2.89, P = 0.004; SIN: t = 2.55, P = 0.009).CONCLUSION In sitting position, stochastic resonance partial-body vibration can improve balance and flexibility while cardiovascular load is low. STOCH can be a valuable training option to people who are unable to stand(e.g., people, who are temporarily wheelchair-bound).