Cognitive cost of motor reorganizations associated with muscular fatigue during a repetitive pointing task.

Muscular fatigue is known to impair motor performance and to catalyse the development of upper limb musculoskeletal disorders. In order to delay the deleterious effects of muscular fatigue, the central nervous system (CNS) employs compensatory strategies. The cognitive cost of such compensatory strategies was assessed in 10 male subjects who alternatively performed two dual-task protocols before and immediately after an exhaustion procedure specific to upper arm abductor musculature. The main motor tasks were an isometric force-matching and a rapid multi-joint pointing. A secondary probe reaction time (RT) task was performed during both protocols and served as an indicator of attentional demands. Overall motor task performance was maintained despite fatigue. Kinematic and electromyographic data revealed that subjects used motor reorganization during the pointing task when fatigued. The RT increased with fatigue in both dual-task protocols, but this increase was significantly higher during the pointing task than during the force-matching task. The results highlight that the motor reorganization used by the CNS under muscular fatigue states require higher attentional demands than the initial motor organization. Finally, the capacity to delay the deleterious effects of muscular fatigue seems to depend on the proportion of cognitive resources available to plan the compensatory motor strategy.