The effect of general anesthesia on passive-knee-extension range of motion

Context: Flexibility is promoted as essential to physical fitness, but the mechanisms limiting it are not fully understood. Objective: To investigate the effects of general anesthesia on hamstring extensibility. Design: Repeated measures. Setting: Hospital operating room. Subjects: Eight volunteers undergoing orthopedic surgeries unrelated to the tested limb. Measurement: Three measurements of passive knee extension (PKE) taken before and after administration of general anesthesia. The force applied during the measurements was consistent between trials. Results: Mean PKE range of motion (ROM) was significantly greater before anesthesia (75.0° ± 11.8°) than after (53.3° ± 17°; t = 5.6, P < .001). Pearson product correlation revealed a significant correlation between the mean difference in PKE ROM between treatment conditions and subjects' body weight (r = .91, P < .05). Conclusions: The findings might be attributable to diminished neural drive to the antagonist muscle groups and suggest a more complex neural control of flexibility than simply neural drive to an agonist muscle.