This thesis consists of five studies, the main objectives of which were to establish a reliable method for conducting surface electromyography (EMG) in water over prolonged submersion (Study 1); to develop a specific method for dividing the contemporary breaststroke leg kick into phases independent of the different techniques used by elite swimmers (Study 2); and to identify the role of neuromuscular activity in effort (Study 3) and performance levels (Studies 4 and 5) in elite contemporary breaststroke swimming. In total, twenty-one participants (twelve students and nine elite swimmers) volunteered to participate. Muscle activation was measured with EMG from eight muscles on the right side of the body. Kinematic variables were measured from twenty-one retro-reflective markers placed on the swimmer's body. Data from these markers were captured in 3D using automatic motion tracking.