Influence of Stretch Speed and Arousal State on Passive Ankle Joint Mechanics

Studies investigating the mechanisms influencing maximum passive joint range of motion (ROM_max) and stiffness have not objectively assessed the possible influence of stretch speed and/or arousal state. The purpose of this study was to assess the effects of arousal state and stretch speed on healthy individuals ROM_max, stiffness, gastrocnemius medialis, and soleus electromyographic activity (EMG). Fourteen participants performed one familiarization and then one testing session on separate days in the laboratory. In the familiarization (Session 1), participants practiced fast (30°/s ankle dorsiflexion) and slow (5°/s) plantar flexor stretches on an isokinetic dynamometer with the knee extended. In the experimental session (Session 2), they performed two slow, then two fast, stretches under three randomized arousal conditions: control (no music), arousing, and relaxing music. Dorsiflexion ROM_max, ankle joint stiffness, muscle activity during stretch, mean heart rate, and perception of arousal were measured. Perception of arousal was greater in the arousing than relaxing condition (p = 0.001). ROM_max was greater during fast (69.1° ± 7.8°) than slow stretches (64.9° ± 10.8°; p = 0.002) with no effect of arousal. Stiffness and EMG were higher at faster speeds, with a significantly greater percentage of stiffness observed in the arousing than the other conditions during faster stretches (p = 0.04). ROM_max was greater at the faster stretch speed despite greater stiffness and muscle activities being produced during the stretch. Thus, despite reflexive muscle activity and viscosity being higher during faster stretches, a greater, not lesser, ROM_max was observed. Arousal state, at least when altered by music, did not seem to affect ROM_max but somewhat influenced stiffness in the faster stretches.