Published online Sep 18, 2018. doi: 10.5312/wjo.v9.i9.156
Peer-review started: March 29, 2018
First decision: May 2, 2018
Revised: May 20, 2018
Accepted: May 23, 2018
Article in press: May 23, 2018
Published online: September 18, 2018
Stochastic resonance whole-body vibration (SR-WBV) is a promising health-intervention at the worksite. In previous works including 4 or even 8 weeks of training, SR-WBV was found to improve musculoskeletal pain and balance, measured as self-report and as recorded body sway on a balance platform. Improved balance is connected to a lower risk of slips and falls. Short trials of SR-WBV that amount to less than 10 min can be done at a worksite without a change of clothes or shoes. Cardiovascular demand with 5 Hz SR-WBV is low and permits SR-WBV in the untrained or elderly workforce.
SR-WBV is practiced in standing position. However, some older individuals and individuals in a wheel-chair may not be able to stand. Therefore, this experimental study investigates partial-body vibration in sitting position and its related acute effects.
The objective of this study was to investigate and quantify the acute effects of partial-body vibration in sitting position on muscle activity, heart-rate variability, balance and flexibility.
The vibration platform used in this study is a functional prototype, constructed specifically for vibration training in sitting position. Every participant attended a baseline and a training condition. For baseline assessment participants sat on the vibration platform without vibration. The training condition was either a sinusoidal partial-body vibration (SIN, 8 Hz) or a stochastic resonance partial-body vibration (STOCH, 8 ± 2 Hz). Surface electromyography (EMG) of the erector spinae (ES), one of the back muscles, and heart rate variability (HRV) were 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 (mSEBT) and flexibility was assessed through the modified fingertip-to-floor method (mFTF).
Paired sample t-test showed a significant increase in balance (STOCH: t = -2.22, P = 0.018; SIN: t = -0.09, P = 0.466) as well as in flexibility (STOCH: t = 2.65, P = 0.007; SIN: t = 1.41, P = 0.086) only after stochastic vibration in sitting position. There was no significant change of muscle activity in the ES-EMG in both training conditions. Also, HRV decreased significantly in both training conditions, but remained in a low-load range (STOCH: t = 2.89, P = 0.004; SIN: t = 2.55, P = 0.009).
This experimental study showed benefits in balance and flexibility only for stochastic but not for sinusoidal vibration. Stochastic vibration in sitting position could be a promising complement to stochastic resonance whole-body vibration in standing position, especially for individuals who are unable for the standing position (e.g., people who are temporarily wheelchair-bound).
As immediate effects of stochastic vibration in sitting position have not been tested before, especially on this prototype device, we needed to make sure that stochastic vibration in sitting position did have the expected effect and that no negative side-effects emerge from one single vibration training in this study. If side-effects would have appeared in healthy people, the device would not be used on an unhealthy sample in the future. As we observed the intended effects, and side effects did not appear in healthy people in this study, this device could possibly be used with patients in future research. Also, further studies should focus on long-term effects of partial-body vibration in sitting position.