When performing team sports such as soccer, rugby and hockey in hot climates, the ingestion of water is often favoured over sports drinks containing carbohydrate. This is because the onset of fatigue under these environmental conditions is typically the result of hyperthermia and dehydration rather than carbohydrate depletion. However, during other modes of exercise conducted in hot environmental temperatures drinking a dilute carbohydrate–electrolyte solution (CES) has been shown to increase exercise performance when compared with plain water. There is currently a dearth of knowledge regarding the benefits that may be derived from consuming these solutions during prolonged, intermittent high-intensity exercise in the heat. One reason for this is the impracticalities associated with measuring core temperature during unconstrained exercise. Therefore, the aim of this thesis was to determine a reliable means of continuously measuring core temperature wirelessly during unconstrained exercise. Thereafter this methodology was used to investigate the influence of ingesting water and a 6% CES during a protocol that closely simulates the demands of intermittent field sports in 30°C.