Pidcoe, PE; Virginia Commonwealth University, Richmond, VA. pepidcoe@hsc.vcu.edu.

PURPOSE: The purpose of this study was to determine if energy expenditure differences exist during the performance of a repetitive stepping activity under a variety of controlled stability conditions. BACKGROUND: Recent trends in therapy include a focus on core (or trunk) stability in an effort to improve subject performance or decrease pain. Exercises on an unstable platform may provide an efficient method of increasing demands on postural control muscles and increase energy expenditure. SUBJECTS: Thirty subjects ranging in age from 20 to 40 years were selected from a college population. This was a sample of convenience and excluded individuals with a history of balance problems. Informed written consent was obtained prior to study initiation. METHODS: Subjects were instructed to perform a cyclical self-paced stepping activity (forward up, backward down) onto a 6-inch high labile platform (Reebok CORE Board) for nine 5-second trials. The trials used combinations of 3 board stiffness settings (low, medium, and high) and 3 foot positions (<12", 12" to 18", >18" apart). The order of trial performance was randomized. Segment motion data, ground reaction force data, and LE EMG data (anterior tibialis and gastroc muscles bilaterally) were collected at 100 Hz, 1000 Hz, and 1000 Hz respectively. ANALYSIS: Force data were used to determine the beginning and end of a complete step cycle. Step cycle segment motion data was used to compute total mechanical energy (translational kinetic + rotational kinetic + potential). Step cycle EMG data was filtered and processed with an RMS algorithm using a 40ms time constant. The energy and EMG data were normalized by total step cycle time. RESULTS: Mechanical energy required per step cycle generally increases as the foot placement width increases and decreased as the surface became stiffer or more stable. The change in mechanical energy was statistically significant (0.05 level) for the most unstable platform setting and the widest foot position trials. LE EMG data showed an increase in activity with step width increase. This was also statistically significant at the most unstable platform setting. CONCLUSIONS: LE EMG and mechanical energy requirements increased as a function of increased foot width and decreased platform stiffness when performing a step-up activity on an unstable platform. Controlling these variables in an exercise protocol may be an effective way to progress the activity and place higher demands on postural control mechanisms. FUNDING SOURCE: Reebok, Inc. (June 2002).

Reprint Information
Requests for reprints should be directed to the corresponding author of the article. Students and other academic customers may receive permission to reprint copyrighted material from Physical Therapy by contacting the Copyright Clearance Center Inc, 222 Rosewood Dr, Danvers, MA 01923. Similar inquiries by all others should be made to the APTA Editorial Office, Attn: Physical Therapy.