UNDERSTANDING PSYCHOLOGICAL INFLUENCE ON HUMAN PERFORMANCE: THE ROLE OF CEREBRAL CORTICAL AND NEUROMUSCULAR ACTIVATION DURING MAXIMAL EXERTION KNEE EXTENSION

Abstract

The dissertation describes a programmatic research effort involving a series of studies (study one, two, three) to address the phenomenon of cognitive strategies facilitating and contributing to enhanced motor performance. Cognitive strategies consist of various mental approaches used before or during the execution of a motor task to improve performance. Psyching, one of the common strategies, typically involves a combination of elements intended to modify arousal and attentional focus to enhance performance. Prior findings within the sport psychology literature have revealed positive effects of psyching on performance, however, the underlying mechanisms of effect are not well understood. To further understand changes in musculoskeletal performance as a result of psyching, the present research used a multidimensional approach (psychological + psychophysiological + kinetic) by employing the measures of electroencephalography (EEG) - cortical activity, electromyography (EMG) - muscle activity, and isokinetic dynamometry - peak torque during maximal exertion to achieve peak torque of a dynamic knee-extension skeletal muscle action. In each of the three studies, participants performed the psychomotor task under three different preparatory strategies, a task-related attentional focus strategy and for comparative purposes mental arithmetic (MA) and reading comprehension (RC) strategies serving as attentional distractions. Participants were characterized as untrained. The results of Study One provide evidence that task-related attentional focus, compared to distracting attentional strategies, is associated with increased force production. The EEG results of study two provide further evidence suggesting that during preparation for movement, the task-related attentional focus distributed neural resources toward task-related regions and away from task-irrelevant regions. Such a phenomena is consistent with the notion of the alpha (i.e., inhibitory) gating as described by Jensen and Mazaheri (2010). A novel contribution of study two was the experimental manipulation of cognitive strategies (RC, MA, PSY) in order to isolate on the element of task-related attentional focus. The primary focus of the program of research was Study Three. Participants were characterized as expert (highly strength trained athletes) with a training status identified as advanced. An additional comparative “resting” condition was implemented to engage the degree of cortical arousal during the three kicking conditions. Individualized alpha power (IAF) as an index as inhibition was subjected to a 4 Strategy (EO, MA, RC, PSY) x 6 ROI (central, frontal, left temporal, right temporal, parietal, occipital) x 4 Time (-20 to -15 s, -15 to -10 s, -10 to -5 s, and -5 to 0 s relative to knee extension initiation) repeated-measures ANOVA. Integrated EMG (iEMG) was subjected to a 3 Strategy (MA, RC, PSY) x 3 Muscle (rectus femoris (RF), vastus medialis (VM) and vastus lateralis (VL)) x 2 Time (-1 to 0 s, 0 to +1 s, respectively corresponding to “pre” and “post” initiation of the knee extension) repeated-measures ANOVA. Peak Torque was subjected to a 4 Strategy (BL, MA, RC, PSY) one-way repeated-measure ANOVA. The BL strategy consisted of maximal exertion during an orientation session in the absence of attentional manipulation. Study three replicated and extended the results of study one and study two suggesting that the use of task-related attentional focus leads to better performance, via the influence of brain and muscle activity. More specifically, enhanced motor performance was achieved via the task-focus cognitive strategy through heightened localized brain activity. In the evaluation of elite athletes, it appears that motor cortex activation is robustly elevated compared to rest across all three strategies in the motor region. Accompanied by heightened inhibition in non-motor regions as a results of the task-related focus. EMG revealed that task-related attentional focus was associated with an increase of neuromuscular activation of the quadriceps muscles. Although beyond the scope of this research, a cascade of events provides a model for explaining the influence of cognitive strategies on maximal skeletal muscle performance. Namely, the focused brain dynamics associated with the task-related focus leads to elevated motor unit recruitment which translates to heightened musculoskeletal performance (peak torque). The findings of this research program extend the neural efficiency model of human performance and support the gating-by-inhibition phenomenon as a central factor. That is, the attentional focus translated to heightened localization of motor activity in the brain resulting in elevated performance.