Effects of exercise on hip range of motion, trunk muscle performance, and gait economy

The purposes of this study were (1) to examine the effects of a passive hip extension stretching exercise program on hip extension range of motion (ROM), (2) to examine the effects of a trunk flexor exercise program on trunk flexor muscle performance, and (3) to examine the effects of passive hip extension stretching or trunk flexor exercises on walking and running economy. ("Gait economy" is defined as the steady-state oxygen consumption per unit of body weight required to walk or run at a specified velocity.)

Twenty-five healthy, athletic, male college students (mean age = 21 years, mean weight = 75 kg, mean height = 172 cm) were randomly assigned to one of three groups: a control group (n = 7), a hip extension stretching group (n = 9), or a trunk flexor exercise group (n = 9).

Before and after 3 weeks of intervention, the following measurements were obtained: right and left hip extension ROM, trunk flexor muscle performance, and walking and running economy. A three x two-way (groups x test sessions) analysis of variance (ANOVA) for repeated measures for unequal subject numbers was performed on each of the five dependent measures, with analysis of simple main effects applied when significant interactions were found.

The ANOVA on right and left hip extension ROM revealed a significant interaction. Analyses of simple main effects showed that 3 weeks (six sessions) of passive hip extension stretching significantly improved right hip extension ROM (pretest = -20.4 degrees, posttest = -8.3 degrees) and left hip extension ROM (pretest = -16.8 degrees, posttest = -7.0 degrees). There also was a significant interaction for trunk flexor muscle performance. The analysis of simple main effects revealed that 3 weeks of daily trunk flexor exercises significantly improved trunk flexor muscle performance (pretest = 41.5 degrees, posttest = 60.4 degrees). The 3-week intervention program of hip extension stretching or trunk flexion exercises, however, did not produce significant changes in walking or running economy.

The results suggest that (1) six treatment sessions of passive stretching were sufficient to improve hip extension ROM; (2) 3 weeks of exercises performed daily improved trunk flexor muscle performance; and (3) training of isolated tasks, such as hip flexibility or trunk strengthening activities, did not produce the desired outcome in the economy of walking or running. Possible reasons for the results are discussed.