Lifting strengths in different exertion heights conditioned on extended legs.

This study recruited seven height-matched healthy males to examine their maximum isometric lifting strengths across 13 exertion heights, ranging from 25 cm to 133 cm in increment of 9 cm. The results showed a nonlinear (increasing-decreasing-increasing) strength-height relationship for all subjects. The subjects' lifting strength was strongest (mean 1253.2 N) at the exertion height of 61 cm and weakest (mean 454.1 N) at the exertion height of 115 cm. Due to a large variability of strength ratio for the weakest individual strength to the strongest individual strength across the 13 exertion heights, ranging from 59.6% to 83.7%, practitioners should be cautious when assessing workers' lifting capacity based on strength testing.