Sustained muscle activity minimally influences dynamic position sense of the ankle

Cross-sectional study.

The purpose of this study was to determine if a sustained fatiguing contraction of the dorsiflexor muscles alters the dynamic position sense (proprioception) and the associated central nervous system processing time of information from the ankle.

Ankle injury has been hypothesized to be related to altered proprioception as a consequence of fatiguing exercise. Previous reports assessing proprioception include tests of motor performance (balance and limb repositioning) or tests of a joint under static conditions. This study used a novel experimental approach to test the effects of exercise on the somatosensory system of the ankle.

Nineteen healthy subjects were tested on their ability to extend the metacarpophalangeal joint of their left index finger when their left ankle was passively plantar flexed (0 degrees-40 degrees, 10 velocities) through a predetermined target angle (20 degrees). Testing occurred before and after a fatiguing contraction of the dorsiflexor muscles.

Subjects accurately indicated the ankle target angle up to ankle velocities of 70 degrees/s (300 ms) both before and after the sustained fatiguing contraction. At velocities above 70 degrees/s all subjects could no longer scale to accurately indicate the target angle with the index finger and consequently overshot the target. The central nervous system processing time was estimated to be approximately 85 milliseconds before and after the sustained contraction.

These results indicate that a sustained activity of the dorsiflexion muscles of the ankle minimally affects dynamic position sense and the ability to process dynamic position sense information. Understanding the impact of exercise on sensory system processing will be integral to establishing the scientific basis for rehabilitation programs that purport to train proprioception.