The maximal oxygen uptake (V-dotO2max) is considered an important physiological determinant of middle- and long-distance running performance. Little information exists in the scientific literature relating to the most effective training intensity for the enhancement of V-dotO2max in well trained distance runners. Training intensities of 40-50% V-dotO2max can increase V-dotO2max substantially in untrained individuals. The minimum training intensity that elicits the enhancement of V-dotO2max is highly dependent on the initial V-dotO2max, however, and well trained distance runners probably need to train at relative high percentages of V-dotO2max to elicit further increments. Some authors have suggested that training at 70-80% V-dotO2max is optimal. Many studies have investigated the maximum amount of time runners can maintain 95-100% V-dotO2max with the assertion that this intensity is optimal in enhancing V-dotO2max. Presently, there have been no well controlled training studies to support this premise. Myocardial morphological changes that increase maximal stroke volume, increased capillarisation of skeletal muscle, increased myoglobin concentration, and increased oxidative capacity of type II skeletal muscle fibres are adaptations associated with the enhancement of V-dotO2max. The strength of stimuli that elicit adaptation is exercise intensity dependent up to V-dotO2max, indicating that training at or near V-dotO2max may be the most effective intensity to enhance V-dotO2max in well trained distance runners. Lower training intensities may induce similar adaptation because the physiological stress can be imposed for longer periods. This is probably only true for moderately trained runners, however, because all cardiorespiratory adaptations elicited by submaximal training have probably already been elicited in distance runners competing at a relatively high level. Well trained distance runners have been reported to reach a plateau in V-dotO2max enhancement; however, many studies have demonstrated that the V-dotO2max of well trained runners can be enhanced when training protocols known to elicit 95-100% V-dotO2max are included in their training programmes. This supports the premise that high-intensity training may be effective or even necessary for well trained distance runners to enhance V-dotO2max. However, the efficacy of optimised protocols for enhancing V-dotO2max needs to be established with well controlled studies in which they are compared with protocols involving other training intensities typically used by distance runners to enhance V-dotO2max.