Comparison of two methods for calculating percent body weight on a tilt table.

Physical therapists commonly treat patients when knowledge of percent weight bearing is desirable during functional lower extremity exercise. The purpose of this study was to compare two methods for calculating percent body weight at different angles of inclination on a tilt table. Twenty healthy subjects were weighed on a spring scale in standing and on a tilt table at 5 degrees increments between 0 and 90 degrees of tilt. Percent body weight at each angle was compared to a value predicted from a trigonometric equation. Predicted values were significantly greater than measured values at all angles greater than 10 degrees of tilt. Predicted overestimation ranged from 2.8 to 14.2%. Compared to the trigonometric method, physical therapists can more easily and accurately determine percent body weight on a tilt table using a scale if total body weight is known. Partial weight-bearing rehabilitation could be performed on the tilt table by varying the degree of inclination, allowing functional lower extremity exercise for patients with weight-bearing restrictions. Guidelines could be established following a variety of injuries and orthopaedic procedures incorporating functional lower extremity exercises at varying percentages of body weight.