Hamstring flexibility increases the same with 3 or 9 repetitions of stretching held for a total time of 90 s.

OBJECTIVE: To determine if stretching for a constant total time with differing repetition durations and number of repetitions over a 6-week period produced different changes in hamstring flexibility measured by knee extension range of motion (ROM). DESIGN: Randomized Control Trial. SETTING: University laboratory. SUBJECTS: 34 volunteers, 18-25 years old with tight hamstrings as determined by a greater than 30° loss of knee extension with hip flexed to 90° participated in the study. MAIN OUTCOME MEASURES: Change in knee extension ROM was assessed in participants who were randomly assigned to a control, or to a stretching group of either 10 s for 9 repetitions or 30 s for 3 repetitions, for a total stretch time of 90 s. Each group stretched 6 days a week for 6 weeks. RESULTS: Pre to post stretch comparison indicated both stretching groups were successful in increasing joint ROM (11.6 ± 5.25°-13.4 ± 5.36°) over the control (F = 19.77, p < 0.003). However, there was no significant difference between the stretching groups (p = 0.9). CONCLUSION: Stretching for 6 weeks for total of 90 s showed increased joint ROM regardless of the number of repetitions or the duration of each individual stretch.