Repetitive low-back-level arm activity to fatigue diminishes limb position sense

• Position sense awareness of the shoulder was determined for 9 males and 9 females before and after performing repetitive low-level arm activity to fatigue. The activity consisted of continuous horizontal internal and external rotations. Position sense awareness tests were performed with subjects blindfolded and seated with the arm in a motorized rig. The subjects were asked to actively reproduce test positions of 10°, 25°, 55° and 70° randomly assigned, while starting at 40° (relative to the sagittal plane). The tests were conducted immediately before and after the fatiguing activity. An ANOVA revealed that the absolute error, measured as test position minus reproduced position, was significantly increased following fatigue for the subjects as a group (p<0.001 ). Furthermore, females had overall higher error than males (p<0.05). The results indicate that repetitive low-level activity to fatigue leads to proprioceptive deficits. These deficits can create a non-optimized motor control, causing an increase in the co-activation of agonist and antagonist muscles and thus increasing the work-load. This could create an unfavorable cycle of events, which would further impact proprioception and thereby enhance the risks for muscle pain and injury. The higher incidence of injuries for female athletes compared to males may be attributed to gender differences in proprioception.

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