Vibration effects on static balance and strength

The purpose of this study was to investigate the effects of a vibration training protocol and a conventional strength training program consisting of similar exercises on knee extensors and flexors strength and postural sway in middle-aged women. 38 women were randomly assigned into a Vibration Group (n=12, static and dynamic exercises on a vibration plate, frequency: 15-25 Hz, amplitude: 2-12.8 cm), a Strength Group (n=16, same exercises without vibration) and a Control Group (n=10). Both experimental groups trained for 12 weeks (3 sessions/w). Static balance was assessed in 3 tasks of increasing difficulty: Normal Quiet Stance, Sharpened Tandem, and One-Legged Stance. Postural sway was evaluated using the Centre of Pressure variations in the Anterior/Posterior and Medio/Lateral direction. Eccentric and concentric strength of knee extensors and flexors was recorded using a Cybex dynamometer. After vibration training, postural sway significantly decreased in both directions for the vibration group in all tasks (p<0.05), whereas no significant differences were observed for the other groups. Isokinetic strength significantly (p<0.05) increased for both experimental groups at selected angular velocities. It was concluded that side-alternating vibration could have beneficial effects on static balance control for middle-aged women. Gains in isokinetic strength were quite similar for both experimental groups.