Because differences between participants, as well as within participants, over time day of consecutive training in outcomes were expected, the intercept was conceptualized as random effect on both levels. Time, prior low back pain, and training effect were set as fixed effects. Hence, the regression model assumed the decrease of MSC and increase in well-being and surefootedness over time only for those absolving SR-WBV but not for those in the control group Hypothesis 1 and Hypothesis 2.
Moreover, the three-way interaction between training condition, time, and prior low back pain tests the assumption that the effect of SR-WBV should be larger in those with prior low back pain compared with those who reported no prior low back pain Hypothesis 3. The multilevel regression model is represented by the following equation:. Subscript i indicates the Level 1 time variable that was assessed on daily basis and j indicates the Level 2 person variable. There was no study attrition.
All participants passed through the 54 days of the study. In daily assessments there were no missing values. However, two participants provided no response to the Nordic questionnaire item on frequency of low back pain episodes in the past 6 months, and three participants failed to report their body weight.
A nonparametric U-test compared all outcome variables on the first day of SR-WBV in those who started in the training group and those who started after 4 weeks waiting group. Groups did not differ significantly in any outcome variable.
Thus, data from both groups were merged. Frequency of low back pain episodes in the past 6 months prior to the study showed no low back pain in 22 participants Thirteen participants reported to experience low back pain less than once a month, eight participants reported episodes once a month, and eight individuals reported to experience low back pain once a week. Two of three correlations between three daily measures of MSC were significant.
Correlations, however, were not that close that measures could be considered redundant. A first test was whether individual musculoskeletal well-being, musculoskeletal pain, and surefootedness showed both, interindividual and intraindividual variation of scores. Thus, total variation was due in equal parts to individual and intraindividual variation. SR-WBV was expected to increase musculoskeletal well-being and surefootedness and to decrease musculoskeletal pain across training days.
A similar result pattern appeared in the prediction of surefootedness. In accordance with Hypothesis 3, Fig. Prediction of daily musculoskeletal well-being, musculoskeletal pain, and surefootedness in multilevel regression analyses. Times ranged between 20 seconds and 30 seconds with many individuals reaching the second mark.
The current study showed that SR-WBV was related to increased musculoskeletal well-being and reduced musculoskeletal pain in those with low back pain. Considering overall usefulness, SR-WBV appeared to be more related to increased musculoskeletal well-being than to reduced musculoskeletal pain. Results are in accordance with other studies on worksite activity trainings to reduce MSC in office work .
SR-WBV effects on muculoskeletal pain, however, also deserved a deeper analysis that tested whether SR-WBV was linked to reduced pain in those who suffered from musculoskeletal pain prior to training whereas those who were pain free benefited less. The overall results of SR-WBV in white-collar employees doing office work mainly working with video display units in predominantly sitting positions replicates findings of SR-WBV in blue-collar workers in a metal manufacturing company .
This finding suggests that whether or not biomechanical loads contribute to muscular complaints, SR-WBV is potentially useful. Studies that compared MSC in nurses who experienced considerable biomechanical loads and office workers found no evidence of different mechanisms leading to nonspecific, recurrent low back pain in the two occupations [1,36].
With respect to sedentary work, studies indicate that sitting is no worse than standing for low back pain incidence . Sitting is not associated with increased pressure to spinal discs. If sitting is a greater threat for the development of low back pain than standing, the mechanism is unlikely to be raised pressure to spinal discs . Physiologically, the advantages of SR-WBV hypothetically arise from large acceleration levels that can still be controlled, from the transfer of mechanical energy to the human body, from the large number of repetitive cycles within short periods of time, and from the specific effects deployed via muscle spindles and mechanoreceptors .
More research is needed to clarify the physiological processes behind SR-WBV related changes, especially the gain in body balance. One promising working assumption is that stochastic vibrations improve information from the periphery of the sensory system by lowering sensory thresholds in neurons located in various joints .
Muscles need this neuronal input to regulate force in order to stay upright. Negative effects of vibration at work are caused due to chronic exposure—with long exposure and short rest cycles—with rather regular vibration that is often oscillating at large amplitude or at frequencies of mechanical resonance .
SR-WBV may have risks and benefits and both should be studied. A review of studies on whole body vibration reported very few side effects 0. More serious side effects have been exclusively found in studies using sinusoidal whole body vibration but not in studies using SR-WBV.
SR-WBV seems to be a safe training intervention with usually harmless adverse effects when a careful evaluation of the medical history is done prior to SR-WBV to evaluate contraindications or potential risk factors of the participants.
In addition, one should avoid unnecessarily large exposures to keep the risk of side effects as low as possible. Therefore, we did the second training, the shortest period known to have a training effect.
An advantage of the study is that no attrition across 56 days was observed and participants also reported no side effects of SR-WBV. Compliance presumably was maintained by the easy training procedure that afforded no change of clothes or change of location and did not last more than 10 minutes.
The limitations are typical for intense worksite training studies. The sample size is moderate and replication with a larger sample is desirable.
Participation rate was also moderate and bias cannot be excluded here. Participants in the next study should be: 1 randomly selected out of the entire sample of employees, and 2 randomly assigned to the training condition and control condition. Additionally, all but one measure were based on questionnaires, which can be subject to a range of biases. Another point of limitation is that participants were blinded with respect to training condition. Participants may be biased due to their belief about the training effect.
This study indicates that SR-WBV may help to reduce musculoskeletal pain in those who suffer from low back pain Moreover, SR-WBV is likely to increase the sense of balance and body balance performance in a standardized test. SR-WBV was shown to be an economic exercise that requires very little effort in terms of infrastructure, time, and effort from participants.
SR-WBV during work may help to prevent occupational low back pain and falls at work. No potential conflict of interest relevant to this article was reported. Elfering, V. Schade, and L. National Center for Biotechnology Information , U. Journal List Saf Health Work v. Saf Health Work.
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In this way, you can make use of noise to boost the signal-to-noise ratio of the system so that even very weak signals can be detected. However, there is an optimal level of noise beyond which the performance of the system starts to deteriorate. Yang said that chaos is commonly seen in optomechanical systems where there is mechanical oscillation.
But instead of creating chaos directly with a weak field, we aimed at creating chaos in a strong field, the pump, and transferring that chaos into a weak field, the probe. And we succeeded. Louis focuses intellectual efforts through a new convergence paradigm and builds on strengths, particularly as applied to medicine and health, energy and environment, entrepreneurship and security. Materials provided by Washington University in St.
Original written by Tony Fitzpatrick. Note: Content may be edited for style and length. Science News. Banerjee, J. E 99 , Benzi, A. Sutera, A. Vulpiani, J. A 14 , L Mcdonnell, D. Abbott, Plos Comput.
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Filatrella, Nanotechnology 28 , Filatrella, Phys. Patel, B. Neural Netw. Hohn, A. Burkitt, Phys. E 63 ,Stochastic Resonance: Theory and Applications deals with the theory of noise-added systems and in particular with Stochastic Resonance, a quite novel theory that was introduced in the s to provide better understanding of some natural phenomena (e.g. ice age recurrence). Following the very first works, a .