Relationship between pulmonary oxygen uptake kinetics and high-intensity running performance in professional soccer players.

The overall aim of this thesis was to identify whether oxygen uptake (VO2) kinetics are a determining factor in the performance of soccer-specific high-intensity exercise. To achievethis aim there were five objectives: 1) to design a protocol for the assessment of VO2 kinetics at the onset and cessation of moderate- and heavy-intensity treadmill running; 2) to assess thereproducibility of VO2 kinetics measured during such a protocol; 3) to quantify thecharacteristics of VO2 kinetics during the onset and cessation of moderate- and heavy-intensity running; 4) to identify if VO2 kinetics discriminate between elite and non-elitesoccer players and 5) to identify the physiological processes (VO2 kinetics, VO2 max, GET, anaerobic capacity) that determine soccer-specific high-intensity running capacity. To establish the day-to-day variability in aerobic markers of moderate- (80%GET) and heavy-(50%Delta) intensity exercise domains, the pulmonary gas exchange of nine participants was measured during an incremental treadmill test to exhaustion on two occasions. Narrow 95% limits of agreement (LOA) and low coefficients of variation (CV) indicated that such markers of intensity were reproducible. Based on these findings, eight participants performed a repeated exercise transition treadmill protocol (six moderate (80%GET) and two heavy (50%A) transitions) on two occasions. Two-way analysis of variance with repeated measures (ANOVA) revealed the phase II time constant (tau[1]) to be invariant across intensity domains for both exercise transients (tau[1]on, moderate 23.2 +/- 2.9 s vs. heavy 23.7 +/-3.1 s; tau[1off] moderate 27.4 +/- 3.5 s vs. heavy 27.1 +/- 2.4 s), while both phase II and III tau were quicker during the onset than cessation of exercise (phase III, tau[2on] 177.5 +/- 43.9 s vs. tau[2off] 396.1 +/- 52.3). The 95% LOA and CV for phase II parameters were small for both intensities and transients of exercise. Conversely, broad 95% LOA were identified for all the phase III parameters. To address this problem, the treadmill protocol was modified to include four very heavy-intensity exercise transients (80%?) to improve the signal-to-noise ratio of the phase III response. Analysis of test-retest data obtained from ten participants revealed that although the CV and 95% LOA for the phase III parameters were improved, they were still larger than for phase II parameters.Using the very-heavy intensity treadmill protocol, a relationship (bivariate correlation) was found between r1on and soccer-specific high-intensity running capacity, both for professional (Pro, n = 18) (r = -0.71; P =0.013) and amateur (Am, n = 18) (r = -0.69; P = 0.014) soccer players. However, the role VO2 kinetics plays in such exercise appears to be limited, as a mixed design two-way ANOVA revealed that the Pro players ran further in a test of soccer-specific fitness (Pro 966 +/- 153 m vs. Am 840 +/- 156 m) despite the VO2 kinetic profiles of the two groups being indistinguishable (tau[1on], Pro 24.5 +/- 3.2 s vs. Am 24.7 +/- 1.8 s; tau[1off], Pro 28.7 +/- 2.8 s vs. Am 29.3 +/-3.5 s). To identify which physiological processes did determine soccer-specific high-intensity running capacity among elite players, a longitudinal study was conducted with 16 Pro soccer players (8 = controls, 8 = training), whose soccer specific fitness, aerobic (VO[2] max, VO[2] kinetics) and anaerobic profiles (anaerobic capacity) were assessed before and after a six week high-intensity training intervention. A two-way ANOVA mixed design revealed soccer-specific fitness (P=0.015) and anaerobic capacity (P = 0.021) were the only measures that increased among the training group following the intervention. The change between the two measures was also correlated (r = 0.89; P = 0.012). It is plausible that due to the sporadic nature and high-intensity of the running performed in soccer, VO2kinetics are not a determinant of performance, and above a certain threshold of aerobic fitness, it is the capacity for anaerobic energy production that is crucial for the performance of soccer-specific high-intensity running.