Despite an increasing number of products available for therapeutic use, the prescription of such devices has a limited experimental foundation. The Hydro-Tone Bell is a product designed to be used as an upper body resistance device underwater. The purpose of this study was to devise a method and an apparatus to measure the force production capability of the Hydro-Tone Bell. It was tested in 2 different orientations and at water velocities varying from 31 cm/sec to 152 cm/sec (1-5 ft/sec). The results of this study show that the Hydro-Tone Bell orientation and water velocity both have a considerable effect on force production. Approximately 50% more force is produced when the Hydro-Tone Bell is positioned at a 45° angle than when it is aligned at 0° at a water velocity of 152 cm/sec (130 versus 80 N or 29 versus 19 lbs). However, at the slowest velocity tested, 31 cm/sec, the forces produced in the 2 orientations are nearly identical (approximately 5 N or 1.1 lbs). As expected, the forces produced in either orientation increase nonlinearly with increasing water velocity (eg, a 2-fold increase in velocity causes approximately a 4-fold increase in force production). Future clinical studies are needed to further investigate the orientations and movements most beneficial for actual therapeutic use. However, this study provides the necessary background information on the potential force production of the Hydro-Tone Bell over a range of functional velocities.
J Orthop Sports Phys Ther. 1996;23(4):267-271.
Key Words: resistive exercise, aquatic, force gradation