Sensory adaptation after a 2-week stretching regimen of the rectus femoris muscle

Objective: To study the effects of a muscle stretching regimen for the rectus femoris muscle on subjective stretch sensation and range of motion (ROM). Design: A 2 X 2 crossover design comprising 2 treatments and 2 intervention periods. Setting: A military base in Sweden. Participants: A volunteer sample of 29 male military conscripts divided into 2 groups, with each group subjected to both experimental and control treatments at different time periods. Intervention: Two weeks of supervised stretching (4 times/wk) of the rectus femoris muscle (experimental treatment) and the calf muscles (control treatment). Main Outcome Measures: Subjective rating of the stretch sensation for the anterior aspect of the thigh determined on a category ratio scale. Passive knee flexion ROM determined on each test with the same applied torque, specific for each subject. Results: An additive analysis of variance revealed that the stretch sensation after the experimental treatment was decreased, compared with the control treatment (p < .01). The knee flexion, however, remained the same regardless of the treatment. Conclusion: Sensory adaptation seems to be an important mechanistic factor in the effect stretching has on ROM changes. The lack of change in knee flexion suggests that the stretching, as performed in this study, did not influence stiffness of the rectus femoris muscle. Sensory adaptation may also be an underlying mechanism in the alleviating effect of stretching when applied to tired, tender, and painful muscles.