Pain sensitivity and torque used during measurement predicts change in range of motion at the knee

OBJECTIVE: To determine the extent to which changes in knee range of motion (ROM) after a stretching program are related to sensory factors at the time of testing and the amount of force used during the measurement of ROM, rather than changes in soft-tissue properties. DESIGN: Randomized, single-blind design. Participants were randomly assigned to a control or stretching group. SETTING: Research laboratory. PARTICIPANTS: Forty-four healthy volunteers (22.8±2.8 years of age; 23 men). INTERVENTIONS: The stretching group undertook static stretching twice a day for 8 weeks. The control group continued with routine activity, but was discouraged from starting a flexibility program. MAIN OUTCOME MEASURES: ROM and tissue extensibility was assessed using a Biodex3 dynamometer, and ratings of thermal pain were collected at baseline and at 4 and 8 weeks by an examiner blinded to group assignment. Multilevel modeling was used to examine predictors of ROM across time. RESULTS: The stretching group showed a 6% increase, and the control group had a 2% increase, in ROM over the 8-week program. However, when fixed and random effects were tested in a complete model, the group assignment was not significant. End-point torque during ROM testing (p=0.021) and the ratings in response to thermal testing (p<0.001) were significant, however. CONCLUSION: ROM measured in a testing session was not predicted by assignment to a stretching program. Rather, ROM was predicted by the ratings of thermal stimuli and the peak torque used to apply the stretch.