Gravitational forces and whole body vibration: implications for prescription of vibratory stimulation

The purpose of this study was to determine the gravitational forces (g-forces) associated with different postures (standing single leg, standing double leg, semi-squat), amplitudes (1.25, 3.0, 5.25 mm), frequencies (10, 20, 30 Hz) and at different anatomical sites (tibial tuberosity, greater trochanter, jaw). Twenty-three subjects underwent whole body vibratory stimulation on a teetering platform that oscillated about a sagittal shaft (Galileo(TM) 2000). The analysis involved collapsing all the data into four categories (frequency, amplitude, posture, damping) and investigating the g-forces within each category. The 20 Hz frequencies resulted in significantly greater g-forces (2.05g) than 10 and 30 Hz (1.83 and 1.76g, respectively). As amplitude increased so to did the g-forces (1.25 mm, 1.6g; 3.0 mm, 1.85g; 5.25 mm, 2.2g; P < 0.05). G-forces associated with the semi-squat (2.34g) were significantly greater (P < 0.001) than the standing postures. Significant damping was observed as the vibratory stimulation was transmitted to the proximal segments (tibial tuberosity, 3.91g; greater trochanter. 1.26g and jaw, 0.34g). Findings were discussed in terms of safe, progressive and effective prescription of vibratory stimulation. (C) 2003 Elsevier Ltd. All rights reserved.