The time course of passive stiffness responses after an acute bout of static stretching has received little research attention, particularly in older adults.
PURPOSE: To determine the time course of the acute effects of static stretching on hamstring passive stiffness in elderly men.
METHODS: Fifteen elderly men (70 ± 7 yrs.) underwent one passive straight-leg raise (SLR) assessment before (Pre) and at 0 (Post0), 5 (Post5), and 10 (Post10) min after two randomized conditions that included a control treatment (quiet resting for 2 min) and a stretching treatment. During the SLR, participants laid in a supine position with the knee braced in full extension. Each SLR was administered manually by the primary investigator who applied force against a load cell attached to the heel, while the leg was moved toward the head. All SLR assessments were performed on the right leg to the point of discomfort, but not pain as indicated by the participant, which was regarded as the max range of motion (ROM). An electrogoniometer was used to measure the hip joint angle. For the stretching treatment, four 15-s SLR static stretches were completed in the same manner as the SLR assessments; however, when max ROM was reached, the leg was held at this position for 15 s. Each 15-s stretch was separated by 15 s of rest. Passive stiffness was calculated during each SLR assessment as the slopes of the initial and final phases of the angle-torque curve.
RESULTS: Passive stiffness (collapsed across phase) was lower at Post0 (0.92 ± 0.27 Nm·°-1; P = 0.029) and Post5 (0.95 ± 0.19 Nm·°-1; P = 0.042) but not Post10 (1.03 ± 0.26 Nm·°-1; P > 0.999) compared to Pre (1.07 ± 0.23 Nm·°-1) for the stretching treatment. There were no significant differences (P > 0.999) in passive stiffness between any of the time points (Pre = 1.07 ± 0.25 Nm·°-1; Post0 = 1.10 ± 0.36 Nm·°-1; Post5 = 1.09 ± 0.24 Nm·°-1; Post10 = 1.06 ± 0.24 Nm·°-1) for the control.
CONCLUSION: These findings showed that hamstring passive stiffness in elderly men decreased after four 15-s SLR static stretches but returned to baseline values within 5-10 min. Given the transient nature of these changes in stiffness, we recommend that acute bouts of SLR static stretching be performed on older adults 5 to 10 min prior to physical activity or exercise, as this may ensure lower stiffness and perhaps, greater performance at the start of the event.