PhD Defense: Kevin Phillips, MS
Department of Kinesiology and Integrative Physiology
The Influence of Temperature on Neuromuscular Fatigue and Prefrontal Cortex Activation During Upper Extremity Exercise
ABSTRACT: Alterations in body temperature (i.e. thermal strain) is experienced by many individuals and can diminish performance during exercise. However, thermal interventions such as cold water immersion may also be used to attenuate fatigue during exercise and accelerate recovery. Currently, there is little research examining how thermal alterations influence brain activation during fatiguing tasks. For my dissertation, I used a variety of methods including functional near-infrared spectroscopy, surface electromyography, electrical stimulation, load cells and psychological questionnaires to investigate how changes in temperature can alter neuromuscular fatigue, prefrontal cortex (PFC) activation, and the perception of discomfort during upper extremity exercise.
I examined how cold ambient temperatures affect climbing specific finger flexor performance. The results showed that exposure to 10 °C for 30 min did not hinder maximal finger flexor strength, however time to failure during the fatiguing task was greater (364 ± 135 vs. 251 ± 97 s; P < 0.01) compared to performance in a thermoneutral environment (24 °C). These results suggest that rock climbers should consider the importance of thermoregulation for improved performance. This study was published in the European Journal of Sport Science.
I investigated how heating and cooling arm musculature prior to exercise influences PFC activation, neuromuscular function and perceptual demands during a fatiguing task of the elbow flexors. Performance of a low intensity contraction for 5 min resulted in greater PFC activation (oxygenation) in the hot (13.3 ± 4.5 μmol/L) and neutral conditions (12.4 ± 4.4 μmol/L) compared to the cold condition (10.3 ± 3.8 μmol/L; P < 0.001). Reductions in maximal strength were greater for the hot (25.7 ± 8.4%) and neutral (22.2 ± 9.6%) conditions compared to the cold condition (17.5 ± 8.9%; P < 0.01). Lastly, rating of muscular discomfort, perceived exertion and task demand were perceived as lower in the cold condition. These results suggest that muscle cooling can reduce the development and perception of fatigue during low intensity exercise.
I explored how passive recovery vs. cold water immersion of the forearms affected repeated climbing specific finger flexor performance, PFC activation, muscle fatigue and perceptual demands. Following the cold water immersion recovery intervention, time to task failure was greater (243 ± 78 vs. 154 ± 43 s; P < 0.001) compared to passive recovery. This improvement was accompanied by a slower increase in PFC activation (3.60 ± 1.64 vs. 5.38 ± 2.63 μmol/L/min; P < 0.01). Additionally, muscle discomfort and muscle fatigue were similar at the end of the fatiguing task, despite a longer time to failure following cold water immersion. These results helped expand our understanding of how climbing performance is improved following cold water immersion of the forearms.
Taken together, these results provide psychophysiological evidence that cooling can improve muscle performance, reduce PFC activation and alleviate perceptual demands during low to moderate intensity fatiguing contractions of the upper extremities.
Monday, April 1 at 10:00 am to 11:00 am
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