Active stretching, performed for three minutes three times per week, resulted in significant improvements in hip flexor passive range of motion among subjects with either normal or limited hamstring flexibility, according to recent research.

The study, “Comparison of active stretching technique in males with normal and limited hamstring flexibility,” involved 138 males with an average age of about 22 years, all of whom reported engaging in moderate physical activity on a regular basis.

In order to establish baseline hamstring flexibility, each subject participated in an initial testing session. The test involved executing a maximum passive straight-leg raise on each leg. The researchers used an inclinometer to evaluate the point of maximum hip flexion, measuring both legs twice and taking the average of the scores.

Those with maximum hip flexion of 80 degrees or greater were placed in the normal hamstring flexibility group, and those with maximum hip flexion less than 80 degrees were placed in the limited hamstring flexibility group. Within each of these groups, subjects were then randomly assigned to either a stretching group or control group.

Both stretching subgroups performed active stretching for 180 seconds three times per week for a total of 12 weeks. The stretching consisted of two unilateral and two bilateral unassisted active stretching exercises. Six sets of hamstring stretching exercises were performed for 30 seconds per set. There was a 20-second rest period between each stretch, during which the hip extensor muscles returned to a neutral position. Subjects in the control period performed no stretches for 12 weeks.

Besides the baseline measurement of maximum hip flexion, participants also were tested for maximum hip flexion at weeks four, eight and 12. For subjects in the stretching groups, hip flexor passive range of motion was always tested two days after the last stretching session.

Results of the research revealed significant improvements in hip flexor passive range of motion among both stretching groups at each four-week testing session. Hip flexor passive range of motion did not improve among subjects in either control group.

“Furthermore, after four and eight weeks of the stretching program, both normal and short hamstring stretching subgroups showed significant improvement in hip flexion [passive range of motion],” state the study’s authors. “Therefore, a plateau effect was not reached.

“However, it should be noted that although the magnitude of improvements in hip flexion [passive range of motion] during the last four weeks were statistically significant, they were lower compared to those in the previous eight weeks,” the researchers continued. “Thus, it may be suggested that the effects of the stretching program were diminishing and a plateau effect may be approaching.”

Authors: F. Ayala, P. Sainz de Baranda, M. De Ste Croix and F. Santonja.

Sources: University of Murcia, Murcia, Spain; University of Castilla La Mancha, School of Sport and Exercise, University of Gloucestershire, Gloucester, United Kingdom; University of Murcia, Spain; and Department of Traumatology, V. de la Arrixaca University Hospital, Murcia, Spain. Originally published in 2012 in Physical Therapy in Sport.