Localized muscle fatigue decreases the acuity of the movement sense in thehuman shoulder

Purpose: The purpose of this study was to investigate alterations in the mo vement sense acuity during localized muscle fatigue in the human dominant s houlder. 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 ove r 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 fron tal plane, at 10% of maximal voluntary contraction (MVC) and 2) Hard exerci se (HE), same movements as in LE, but performing MVC to fatigue. Results: T he results showed that subjects had a lower probability of distinguishing b etween different movement velocities following HE as compared with those du ring the LE condition (P < 0.001). When genders were compared, female subje cts 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 possibl e influence of muscle fatigue via peripheral muscle receptors on movement s ense is discussed.