No abstract

To clarify the effects of whole-body vibration (WBV) on visual performance, visual acuity and a self-rated assessment of difficulties in visible perception were determined after various frequencies of vibration in six healthy males. Two different sitting postures , an erect posture and a muscle-relaxed posture, were used. Sinusoidal vertical vibrations at ten frequencies (8, 10, 12.5, 16, 20, 25, 31.5, 40, 63.5 and 80 Hz) were applied to the seated subjects for 20 sec. The magnitude of acceleration at each vibration frequency was maintained at 2.5 msec-2 (r.m.s.). The visual performance was evaluated by a standard visual acuity test and a self-rated assessment for difficulties in visible perception. The disturbances of visual performance were dependent on the vibration frequency (p<0.01, ANOVA) with a maximum reduction of visual acuity at a frequency of 12.5 Hz. The disruption of the visual performance was more severe with the erect posture than with the muscle-relaxed posture. In conclusion, short-term WBV exposure can affect visual performance, depending on the vibration frequency and the sitting posture. The visual acuity and self-rated assessment of disturbances of vision may be influenced by the resonance frequency of the eyeball.

The influence of whole-body vibration on gastric motility was investigated by using an electrogastrography (EGG) in seven healthy men. The EGG is usually referred to as a noninvasive technique of recording gastric myoelectrical activity by means of placing electrodes on the abdominal surface. Sinusoidal vertical vibration at each of 3 different frequencies (10 Hz, 20 Hz, 40 Hz) were randomly given to the subject seated on a platform of vibrator for 5 min. The vibration magnitude was kept at a constant of 2.0 msec-' (r.m.s.) during operation. The mean dominant frequency of EGG at control period was prior to operation 3.3 cycles per min (cpm). During vibration exposure at 10 Hz, the peak of dominant frequency increased to 3.9 cpm, and the relative power of slow wave showed the statistically significant decrease (45.8%, p<0.05). The mean relative power of slow wave which is composed of frequencies ranged from 2.0 to 5.0 cpm was 56.6% at control period. On the contrary the mean relative power of frequencies ranging from 5.0 to 9.0 cpm, tachygastria increased from 29.5 % to 39.1 %. These results suggest that the short-term exposure to whole-body vibration effects on the gastric myoelectrical activity.

The palmar sweating reaction to vibration stress was related to the background level of the autonomic nerve tone. The sweating volume was in direct proportion to the acceleration magnitude of vibration. The reaction of palmar sweating to vibration stress may be mediated through both the adrenergic and cholinergic fibers of the autonomic nervous system.

These results suggest that short-term exposure to WBV can suppress the gastric myoelectric activity, the responses on which may be mediating by neurohumoral effects as well as the mechanical effect of WBV.