Localized Muscle Fatigue Decreases the Acuity of the Movement Sense in the Human Shoulder

Purpose: The purpose of this study was to investigate alterations in the movement sense acuity during localized muscle fatigue in the human dominant shoulder.

Methods: Fourteen healthy volunteers (8 males and 6 females) with a mean age 23 +/- 2 yr participated in the study. The subjects' ability to discriminate movement velocity relative to a reference velocity imposed over the dominant shoulder was tested following two experimental conditions: 1) Light exercise (LE), repetitive isokinetic horizontal flexion/extensions at the shoulder, ranging from 85 degrees to 20 degrees relative to the frontal plane, at 10% of maximal voluntary contraction (MVC) and 2) Hard exercise (HE), same movements as in LE, but performing MVC to fatigue.

Results: The results showed that subjects had a lower probability of distinguishing between different movement velocities following HE as compared with those during the LE condition (P < 0.001). When genders were compared, female subjects had a lower probability of distinguishing correctly than male subjects (P < 0.001).

Conclusions: The acuity of the movement sense in the dominant shoulder is reduced in the presence of shoulder muscle fatigue. The possible influence of muscle fatigue via peripheral muscle receptors on movement sense is discussed.