Passive Stiffness and Maximal and Explosive Strength Responses After an Acute Bout of Constant-Tension Stretching

Context: Constant-tension (CT) stretching has been used to reduce hamstrings passive stiffness; however, the time course of hamstrings stiffness responses during a short bout of this type of stretching and the effects on maximal and explosive strength remain unclear. Objective: To examine the time course of hamstrings passive-stiffness responses during a short, practical bout of manual straight-legged-raise (SLR) CT passive stretches and their effects on maximal and explosive strength in healthy young women. Design: Descriptive laboratory study. Setting: Research laboratory. Patients or Other Participants: Eleven healthy women (age = 24 +/- 4 years, height = 167 +/- 4 cm, mass = 65 +/- 8 kg) participated. Intervention(s): Participants underwent four 15-second SLR CT passive stretches of the hamstrings. Main Outcome Measurement(s): Hamstrings passive stiffness was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle-torque curves generated before and after the stretching intervention and at the beginning of each 15-second stretch. Hamstrings peak torque and rate of torque development were derived from maximal voluntary isometric contractions performed before and after the stretching intervention. Results: The slope coefficients (collapsed across phase) for the third and fourth stretches and the poststretching assessment were lower than the prestretching assessment (P range = .004-.04), but they were not different from each other (P > .99). In addition, no differences in peak torque (t(10) =-0.375, P= .72) or rate of torque development (t(10) = -0.423, P = .68) were observed between prestretching and poststretching. Conclusions: A short bout of SLR CT passive stretching may effectively reduce hamstrings stiffness without negatively influencing maximal and explosive strength.