In resistance training the weight lifted and the repetitions completed can be altered in order to maximise muscle growth. The American College of Sports Medicine suggests that short-moderate rests (30-90s) between sets is ideal for increasing concentrations of ‘anabolic’, muscle building, hormones, with the assumption that these ‘growth’ hormones drive the muscle building response. However, others contest the role that these ‘growth’ hormones play in muscle building. Muscle building is extremely important to many athletes, and so evidence to support long or short rest intervals for optimal muscle growth is needed. Therefore, the aim of this research is to gain a greater understanding of how rest interval length influences the long-term muscle building response to resistance training. The findings from this study will be published in scientific journals and presented at international conferences with the aim of changing the way athletes across the world train to maximise muscle mass gains with resistance training.