Despite several studies that have considered race performance, none have described the potential changes in technique that occur during the stressful conditions of maximal repeat sprinting often used in training. The aims of this article are to assess the effect of repeated sprinting and muscular fatigue on butterfly swimming technique, and to discuss the applications and implications of this research to coaching and training. Summary Points: When butterfly swimmers are tired … - The hand speed during Insweep and Upsweep is reduced, implying that propulsion is also reduced. This reduction is likely to be as a result of less effective actions of the biceps and triceps muscles, limiting the movement at the elbow; - The direction of propulsion generated by the hand during the Insweep and Upsweep is more inward and outward, rather than backward. It is likely that the limited movement at the elbow hinders the effective use of hand generated propulsion; - They spend longer between propulsive phases (i.e. in the Recovery and Catch). It is likely that swimmers slow down and speed up more in these phases when tired, increasing the energy cost of swimming; - The torso is less streamlined during the Recovery meaning that swimmers experience more resistance. It is likely that the swimmers brake during the initial part of the Recovery when tired, again increasing the energy cost of swimming. Practical Implications for Coaching: - Monitoring both stroke rates and stroke counts (the number of strokes a swimmer takes per lap), will allow a coach to assess whether a swimmer`s technique is breaking down. If a swimmer`s technique breaks down when they are tired in training, this will more than likely become their default setting when they get tired during a race. - Technically, swimmers should be coached to: 1) accelerate their hands back and out during the Upsweep; 2) maintain a flatter torso during the recovery (it is especially important that a swimmer`s chin remains on the surface of the water when breathing); 3) recover the hands low over the water; 4) limit the time spent gliding in the Catch phase of the stroke. - As part of a supplemental dry-land conditioning programme, both functional strength and specific power exercises should be incorporated into a swimmer`s training programme. - The principle of progression should be adhered to so that the necessary specific physiological adaptations to high intensity pool-training can be made without a swimmer`s butterfly technique breaking down. With this in mind, coaches should reflect on the specific aims of prescribed butterfly training sets. When planning training cycles, small and regular butterfly training sets, rather than large infrequent ones may be best. - When devising race tactics, coaches should consider pacing strategies for butterfly swimmers (e.g., going out fast but comfortable, for the first quarter of a race). Such strategies should be incorporated into training programmes and practised well in advance of major competitions.