The aim of this thesis was to identify physiological factors associated with decision making performance of soccer players. If a decrement in decision-making performance was observed, a second aim would be to assess the extent to which soccer players' decision-making capability could be improved and trained. To achieve these aims there were four specific objectives: 1) To measure decision-making in soccer players using a soccer-specific protocol to assess decision-making and determine the reproducibility of the protocol's measures; 2) determine the effect of soccer-specific intermittent exercise on decision-making capability of soccer players; 3) assess the influence of repeated sprints and sprint-recovery duration on decision-making performance of soccer players and 4) assess the extent to which decision-making can be trained, by comparing perceptual video training with a soccer-specific field-based perceptual training programme.Reproducibility of decision-making measures was determined by test-retest method. Ten male participants performed 10 decision-making test trials, rested for one hour then completed a further 10 trials on two occasions. Analysis revealed response time Intraclass Correlation Coefficient (ICC) = 0.91 and response accuracy ICC = 0.80. Coefficient of variation for response time was 3.4% and for response accuracy 4.6% indicated measures were reproducible. Using this protocol, 15 participants performed an experimental trial (decision-making task, before and after an intermittent treadmill protocol) and a control trial (before and after decision-making task) on separate occasions. Means were compared using a fully repeated measures factorial analysis of variance. There was an interaction for response time (p < 0.01), d = 0.64 (large) and an interaction in response accuracy (p < 0.01), d = 0.84 (large) which indicated that players' decision-making performance was impaired probably because of the physiological strain imposed.Investigating these findings, 10 male participants performed, the decision-making task separated by 10 x 10-s repeated sprints with either a 15-s or a 30-s recovery period on different occasions. Means were compared using a fully repeated-measures factorial analysis of variance. There was an interaction for response time (p < 0.01), d = 0.42 (moderate). There was also an interaction for response accuracy (p < 0.01), d = 0.85 (large) highlighting, response time and accuracy were adversely affected as a consequence of the repeated sprints.As a decrement in decision-making was observed, 24 male participants were divided randomly into one of four groups (control, placebo, perceptual training and a field-based decision-making training group) of six participants. Repeated sprints and decisionmaking performance was assessed before and after a six-week perceptual training intervention and during a retention test after a further seven days. Groups were compared using a two-way multivariate analysis of variance, by groups and occasion. Players who underwent field-based training improved their response time (p < 0.01), d= 0.34 (small) and response accuracy (p < 0.01), d = 0.88 (large) after the six-week training intervention. This illustrated that field-based decision-making training facilitated the acquisition of perceptual skill in soccer and could be used as part of players' overall training programme
