THE EFFECT OF TIME ON STATIC STRETCH ON THE FLEXIBILITY OF THE HAMSTRING MUSCLES

Background and Purpose. To date, there are no reports comparing durati on of static stretch in humans on joint range of motion (ROM) and hams tring muscle flexibility. The purpose of this study was to examine the length of time the hamstring muscles should be placed in a sustained stretched position to maximally increase ROM. Subjects. Fifty-seven su bjects (40 men, 17 women), ranging in age from 21 to 37 years and with limited hamstring muscle flexibility (ie, 30 degrees loss of knee ext ension measured with femur held at 90 degrees of hip flexion), were ra ndomly assigned to one of four groups Three groups stretched 5 days pe r week for 15, 30, and 60 seconds, respectively. The fourth group, whi ch served as a control group, did not stretch. Methods. Before and aft er 6 weeks of stretching flexibility of the hamstring muscles was dete rmined by measuring knee extension ROM with the femur maintained in 90 degrees of hip flexion. Data were analyzed with a 4x2 analysis of var iance (group xtest) for repeated measures on one variable. Results. Th e data analysis revealed a significant group xtest interaction, indica ting that the change in flexibility was dependent on the duration of s tretching. Further Post hoc analysis revealed that 30 and 60 seconds o f stretching were more effective at increasing flexibility of the hams tring muscles (as determined by increased ROM of knee extension) than stretching for 15 seconds or no stretching. In addition, no significan t difference existed between stretching for 30 seconds and for 1 minut e, indicating that 30 seconds of stretching the hamstring muscles was as effective as the longer duration of 1 minute. Conclusion and Discus sion. The results of this study suggest that a duration of 30 seconds is an effective time of stretching for enhancing the flexibility of th e hamstring muscles. Given the information that no increase in flexibi lity of the hamstring muscles occurred by increasing the duration of s tretching from 30 to 60 seconds, the use of the longer duration of str etching for an acute effect must be questioned.