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Background: Whole-body vibration (WBV) is established in rehabilitation, in physiotherapy and in sports. WBV may potentially stimulate sensorimotor processes. Recent reviews revealed positive effects on muscle force, postural control, pelvic floor, bone density and musculoskeletal complaints. On this account WBV might be important in deconditioned persons such as frailty, patients with musculoskeletal complaints or after stroke, Parkinson‘s disease or multiple sclerosis for skilling up. The research focuses on the use of WBV, which is carried out in standing position. But only a few studies examined partial-body vibration (PBV) in sitting position. For this reason a PBV device has been developed for sitting. Purpose:The aim of this single case studywas to evaluate trunk muscle activity and acceleration propagation in sitting position during PBV with different vibration parameters. Methods: A vibrating plate with three rotational degrees of freedomwas used which lets the operator to choose a rotation axis, amplitude (◦), frequency (Hz) and the underlying sinusoidal or stochastic nature of the oscillation. Sinusoidal (S-PBV) and stochastic (ST-PBV) with amplitudes from 0.1◦ to 1◦ and frequencies from 1Hz to 12Hz were applied in anterior-posterior and medial-lateral direction. Muscle activity (EMG) and acceleration propagation (3-axis accelerometers) during PBV in sitting position in a 26-yearold healthy male were examined. EMG was measured for M. erector spinae (ES, left, height L4), M. obliqus externus abdominis (OE, left), M. trapezius ascendens (TA, left) and M. trapezius descendens (TD, left). Acceleration was captured on the vibrating plate, on the spinal processes of L4 and C7 and on top of the cranium in medial-lateral (ML), in anterior-posterior (AP) and in cranial-caudal (CC) direction. EMG data during vibration was normalized against the activity during maximum voluntary contraction (MVC). Results: AP and ML accelerations were highest on the vibrating plate and continuously degreased up to the cranium. CC accelerations were low on all levels. The highest mean acceleration on the bodywas observed at L4 during ST-WBV with 18.9m/s2. In general, ST-PBV resulted in higher mean accelerations but had smaller peak accelerations compared to S-PBV. The ES showed the highest relative mean activations with 2.9–7.3% MVC. AP and ML oscillations determined a slightly higher ES-activation during ST-PBV compared to S-PBV. Conclusion(s): Decreasing accelerations were observed with increasing distance from the vibrating plate due to damping properties of involved body structures. Higher activation of muscles closer to the vibrating plate was found. The decrease in muscle activation was related with a decrease of acceleration (body motion), what is plausible from a biomechanical point of view. Erector spinaemuscles seem to invoke highermuscle activation during ST-PBVcompared to S-PBV. This effect is similar to recentfindings fromother authors.We account this to the higher mean accelerations resulting from ST-PBV, in fact higher loads towhich the bodyhas to respond. Implications: ST-PBV should be preferred in practice because of two reasons. Firstly, higher mean accelerations can be reached with lower peak accelerations (shocks) and secondly, the resulting muscle activation seems to be higher compared to S-PBV. |
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