Physiological response to brief maximal intermittent exercise: with particular reference to testing procedures and performance determinants
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Purpose: The activity patterns of many sports are intermittent in nature, fluctuating randomly from brief periods of maximal or near maximal work to longer periods of moderate and low intensity activity. Attempts to examine the complex energy demands of this type of work have typically utilised repeated bouts of brief (< 6-s) maximal work interspersed with relatively short (< 60-s) recovery periods. However, despite years of research, many issues concerning the physiological response to this type of activity remain unresolved. The principal aim of the present thesis was to focus on one of these issues, namely the influence of aerobic fitness on sport-specific repeat sprint ability. Methods: Physically active students from the University of Edinburgh were used in all studies. Each investigation utilised two distinct maximal intermittent (20 x 5-s) test protocols with contrasting recovery periods (10-s or 30-s). The protocols were designed to simulate the range of work to rest ratios often experienced in sports such as badminton, rugby, soccer, and squash. All tests were conducted on a friction-braked cycle ergometer. Results: Both of the intermittent test protocols were found to have good degrees of test-retest reliability in measures of power output and fatigue. Moreover, the highest degrees of test-retest reliability were found to occur after the administration of two familiarisation trials. Although the quantification of fatigue during intermittent work had received a number of different approaches, the percentage decrement score was determined as the most valid and reliable means of assessing this parameter. Differences in recovery duration between the two intermittent test protocols had considerable effects on measures of maximum power output, mean power output, blood lactate, and fatigue. Between-protocol differences in maximum power output were attributed to the potentiation effect associated with Protocol 2 (30-s rest periods). In contrast, differences in mean power output, blood lactate and fatigue were most likely the result of between-protocol differences in the magnitude of the phosphocreatine (PCr) contribution to each sprint. Relative to controls, training-induced improvements in aerobic fitness, as evidenced by a 10.2% increase in V02max, corresponded with substantial improvements in intermittent performance measures of maximum and mean power output (range: 3.2 to 8.2%). Endurance training also impacted on the ability to resist fatigue, the magnitude of which increased with increasing recovery duration. Correlations between V02max and fatigue were also dependent on recovery duration supporting the idea that the principle role of aerobic metabolism during brief maximal intermittent work is in the iii restoration of homeostasis during intervening rest periods. Conclusions: The ability to produce and maintain high power outputs during prolonged periods of brief maximal intermittent work is an important determinant of performance in many sports. The results of the present thesis demonstrate the considerable influence of aerobic fitness in this respect, the magnitude of the effects being largely determined by the duration of the intervening rest periods. Although the precise mechanisms of action require further investigation, the improvements in repeat sprint performance that accompany increases in aerobic fitness are likely to be the result of enhancements in the recovery of power output via improved offtransient inorganic phosphate and PCr kinetics.