The Effect of Motor, Cognitive, and Combined Fatigue on Motor Performance, Retention, and Transfer.

This dissertation aimed to synthesize existing literature on acute state motor and cognitive fatigue within a military population. Significant effort has aimed to explore the underpinnings of human fatigue, how it is perceived and appraised, and subsequent impacts on motor performance capabilities. Despite extensive exploration, a notable gap exists in exploring the combined effects of fatigue on subsequent motor performance within a controlled laboratory setting. To our knowledge, no study has examined the interaction between performance and learning under a state of combined fatigue, nor the transferability of skills acquired in practice to combat-specific environments.

Study one served as a foundational study and aimed to compare the effects of isolated fatigue (motor, cognitive fatigue) and combined fatigue on subsequent motor performance. In support of previous findings, results demonstrated that isolated motor and cognitive fatigue resulted in slower anticipatory reaction time. Notably, findings demonstrated the compounding effect of simultaneous motor and cognitive fatigue, resulting in performance deterioration that exceeded the additive effects of isolated fatigue alone.

Study two aimed to extend these findings by examining whether the observed effects would generalize to the military population, enhancing the ecological validity and increasing the applicability to real-world military operations. Consistent with study one, results demonstrated decreased military marksmanship performance following isolated motor and cognitive fatigue. Additionally, results demonstrated a negative, additive effect on marksmanship accuracy and effect when compared to isolated fatigue.

Study three aimed to expand these results further by exploring the impact of fatigue during practice on skill performance, acquisition, and transfer to real-world combat tasks. Results indicated that practice that incorporates similar demands of the performance environment resulted in improved skill acquisition and transfer. For instance, participants who practiced under fatigued conditions outperformed those who trained without fatigue when assessed during retention and transfer testing conducted under fatigue. These findings suggest that skill learning and transfer are context-dependent and contingent on the similarity of training to performance environments.

This dissertation not only contributes to the mechanistic influence of fatigue, but more importantly, demonstrates the importance of nesting task-specific training to improve motor performance, learning, and transfer.

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