Vibration exposure and biodynamic responses during whole-body vibration training.

PURPOSE Excessive, chronic whole-body vibration (WBV) has a number of negative side effects on the human body, including disorders of the skeletal, digestive, reproductive, visual, and vestibular systems. Whole-body vibration training (WBVT) is intentional exposure to WBV to increase leg muscle strength, bone mineral density, health-related quality of life, and decrease back pain. The purpose of this study was to quantitatively evaluate vibration exposure and biodynamic responses during typical WBVT regimens. METHODS Healthy men and women (N = 16) were recruited to perform slow, unloaded squats during WBVT (30 Hz; 4 mm(p-p)), during which knee flexion angle (KA), mechanical impedance, head acceleration (Ha(rms)), and estimated vibration dose value (eVDV) were measured. WBVT was repeated using two forms of vibration: 1) vertical forces to both feet simultaneously (VV), and 2) upward forces to only one foot at a time (RV). RESULTS Mechanical impedance varied inversely with KA during RV (effect size, eta(p)(2): 0.668, P < 0.01) and VV (eta(p)(2): 0.533, P < 0.05). Ha(rms) varied with KA (eta(p)(2): 0.686, P < 0.01) and is greater during VV than during RV at all KA (P < 0.01). The effect of KA on Ha(rms) is different for RV and VV (eta(p)(2): 0.567, P < 0.05). The eVDV associated with typical RV and VV training regimens (30 Hz, 4 mm(p-p), 10 min.d(-1)) exceeds the recommended daily vibration exposure as defined by ISO 2631-1 (P < 0.01). CONCLUSIONS ISO standards indicate that 10 min.d(-1) WBVT is potentially harmful to the human body; the risk of adverse health effects may be lower during RV than VV and at half-squats rather than full-squats or upright stance. More research is needed to explore the long-term health hazards of WBVT.