Field hockey is a fast moving territorial sport involving bouts of high-intensity energy release, separated by periods of low-intensity activity (Boyle, Mahoney & Wallace, 1994) which has undergone considerable change. The implications of such changes on playing position and fatigue experienced during single match-play or during a tournament environment have not been extensively studied. The research presented in this thesis was undertaken to examine the physiological demands of elite-standard women's field hockey, assess whether the physiological strain is independent of playing position and investigate the demands of tournament match play and potential benefits of nutritional supplements. Study one highlighted the match play demands of women's field hockey. Players spent the majority of match play engaged in low-intensity activity (55.5%), while moderate (38.1%) and high-intensity (6.4%) activity accounted for the remaining time. Players in a forward position had notably different activity patterns, spending a greater percentage of play at high-intensity and covering a greater percentage of distance sprinting than other outfield positions (P<0.001). Study 2 demonstrated that players experienced a 12% decline in second half sprinting distance and a 7.8% decline in the distance covered at high-intensity. The percentage time performing low-intensity activity (P<0.001) increased in the second half, whilst the percentage time performing moderate (P<0.001), and high-intensity (P=0.002) activity declined. Study 3 demonstrated that over the duration of a multinational tournament players experienced a 9.2% and 3.4% decrement in total distance and mean speed. Whilst high-intensity activity was maintained, low-intensity activity increased. Study 4 investigated the effects of tournament play on match analysis and biochemical markers of immune and endocrine function and muscle damage. A rise in creatine kinase (CK) following matches played on a consecutive days (F=0.015) did not influence match play activity patterns. Study 5 demonstrated that sodium bicarbonate did not improve prolonged intermittent running or hockey skill performance, however did show that a split dose protocol was effective in inducing metabolic alkalosis prior to exercise. Study 6 investigated the effects of caffeine on prolonged intermittent running, hockey skill performance and cognitive function. No improvements were observed in performance, however, reaction time in complex cognitive function was enhanced. The data from the experimental chapters presented in this thesis demonstrate that tournament play can result in a change in player's match activity profiles and a decrease in match intensity, whilst fatigue during single match play was manifested as a second half reduction in high-intensity activity and sprint distance. Sodium bicarbonate and caffeine had no performance enhancing effect during prolonged intermittent running and hockey skill test performance. This may have been a reflection of the overall intensity of the exercise protocols replicating the minimum demands of field hockey.