Whole body vibration training: characterization and analysis.

Human reactions to vibration have been extensively investigated in the past. [9, 18, 19, 23]. Vibration, as well as whole-body vibration, was commonly considered as an occupational hazard and it has been highlighted for its detrimental effects on human condition and comfort. It is normally associated with lower back disorders [8], muscle and nerve tissue damage [33], Raynaud’s Disease (vibration white finger) [25] and interference with cognitive processes such as that required for short-term memory. [44] Although vibration may produce undesirable side-effects, different studies have shown the positive impacts of vibration upon the bone density of postmenopausal women and disabled children [42, 48, 52], back pain [37], stroke [47], multiple sclerosis [43] and muscle spasticity of cerebral palsy sufferers [1]. Physiologists and physiotherapists have also been reported to use vibration as a therapeutic intervention such as for clearing the lungs and improving joint mobility [23]. Vibratory stimulations were studied for their positive action in eliciting muscle activity. It is well known, in fact, that local tendon vibrations induce activity of the muscle spindle Ia fibers, and that a reflex muscle contraction known as the Tonic Vibration Reflex (TVR) arises in response to such vibratory stimulus. The change in the length of the muscle produced by the applied vibratory stimulus is detected by muscle spindles and induces reflex and adaptive responses. [3] Training with vibration extended to the whole body, that is Whole Body Vibration (WBV), was initially proposed as a possible application of the Tonic vibration reflex occurrence to the entire body. [4, 6] Indeed, if a localized vibratory stimulus produced elicited muscle activity, then whole body vibration, if properly delivered, could obtain similar muscular activity in all the body muscles. The aim of WBV training (WBVT) is to mechanically activate muscles by eliciting similar stretch reflexes that occurred for localized application of vibration. Dr. Vladimir Nasarov, a chairforsportsbiomechanics at the State College in Minsk, was one of the first to apply vibratory stimulation to help athletes in physical training. Vibrations were applied to the distal muscles and then transmitted through the body chain to the proximal muscles. He used a special device to generate vibrations at a frequency of about 23Hz. Nasarov experiments highlighted the potential benefits of training with vibration to muscular development and peripheral circulation improvement. [32] Although literature has largely analyzed and documented the effects of WBV in electing neuromuscular, metabolic and hormonal responses, the exact mechanisms that are accountable for those effects are still unclear. WBV training is clearly different from localized vibratory stimulation; rarely studies on WBVT monitored the local muscle stimulation (acceleration and displacement) and accounted for motion artifacts presence on EMG recordings. However, it is important to understand the neuro-physiological mechanisms involved in muscle activation under vibration stimulation in order to prescribe safe and effective WBVT programmes. [12]