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.