Position sense acuity is diminished following repetitive low-intensity work to fatigue in a simulated occupational setting

Repetitive work to fatigue is soundly associated with work-related musculos keletal disorders (WMSD), although the underlying mechanisms are poorly und erstood. In the present study, we tested the hypothesis that fatiguing work leads to proprioceptive deficits, which can be an initiating factor for th e occurrence of WMSD. Thus, the position sense of the shoulder was determin ed for 13 males and 13 females before and after performing repetitive low-i ntensity arm work to fatigue in a simulated occupational setting. From a st arting position of 45 degrees to the sagittal plane, position sense tests c onsisted of subjects attempting to actively reproduce target positions of h orizontal movements to 15 degrees and 30 degrees (shoulder adduction) and t o 60 degrees and 75 degrees (shoulder abduction). An analysis of variance r evealed that the absolute error was significantly increased following fatig ue for the subjects as a group (P < 0.001). Furthermore, females had an ove rall higher error than males (P < 0.01). No difference in error was detecte d for the shorter movements versus the longer movements. However, the overa ll absolute error for adduction was significantly higher than for abduction (P < 0.001). The results of the present study support the hypothesis of di minished proprioceptive acuity following low-intensity work to fatigue. A r eduction in position sense acuity could lead to impairment in motor control , which would further impact on position sense. Thus, a vicious cycle may b e activated that might result in WMSD. The poorer position sense acuity obs erved for females may contribute to the explanation of why females demonstr ate a higher incidence of WMSD than males.