Short-Term Effect of Correcting Leg Length Discrepancy on Performance of a Forceful Body Extension Task in Young Adults

In this study we assessed the short-term effect of correcting leg length discrepancy on a vigorously performed task of resisted full body extension in 10 men, 18 to 35 years old, who had estimated leg length discrepancies of 10-15 mm. Using a cable ergometer we examined work performed, initial peak tension exerted on the ergometer, second peak tension, time to first peak tension, and mean velocity of the whole task. Each subject performed the task both with and without a heel lift, introduced to equalize leg length. The interval between testing under these two conditions was 48 hr. In the task of pulling the cable upward, each subject began from floor level with knees and trunk flexed, progressing to full body extension with the arms pulling the cable overhead with maximal effort. For each trial the task was repeated 15 times, with intervals of 90 seconds between the repetitions. Use of the lift failed to have a statistically significant effect on any of the variables, although it clearly enabled three of the subjects to exert greater strength with the arms and trunk during the second peak tension. This suggests that 1) overall body extension is influenced by too many factors to be affected in a consistently predictable way by a heel lift to correct leg length discrepancy, and 2) the heel lift may aid certain subjects with leg length discrepancy specifically during extension of the trunk in this task.