Exercise performance and capacity are both impaired in hot compared to moderate environments although the mechanisms behind the premature termination of exercise are not fully understood. It is clear that the development of hyperthermia plays an integral role and so a variety of cooling interventions have been investigated in an attempt to attenuate the reduction in exercise performance and capacity observed. Cooling the torso has received substantial attention however, based upon data from animal, human and modelling studies, cooling the neck has been proposed as a more effective site to cool. The current thesis investigated the effect of a cooling collar on running performance and capacity in hot conditions (30-32°C; 53% rh). The thesis also examined the effect of the cooling collar on the physiological, perceptual and neuroendocrinological responses to the exercise bout. Chapter 4 reported that 15 min time-trial running performance was impaired by 9.8% in hot (30°C), compared to moderate (14°C), conditions. The application of the cooling-collar improved 15 min time-trial performance in a hot environment (30°C) in subsequent studies by ~6 % and ~7 % (Chapters 5, 6 and 8 ); attenuating much of the impairment in performance observed in Chapter 4. The improvements were observed without alterations in the physiological or neuroendocrinological response to the exercise bout. The rating of perceived exertion was also unaffected, although the collar positively altered the perception of thermal sensation. Cooling the neck also improved exercise capacity in a hot environment (32°) (by ~14% ) due to a dampening of the perceived level of thermal and cardiovascular strain. Chapter 7 reported that cooling the neck had no performance benefit when the body was under insufficient thermal strain while Chapter 8 reported that there is a limit to the performance improvements that can be achieved. The data presented within the current thesis demonstrates that cooling the neck via a practical neck collar can improve running performance and capacity in a hot environment; this improvement has many potential advantages for athletes and coaches.