Muscle hypertrophy is an often sought goal of athletes and mere mortals alike. The basis of hypertrophy resides predominantly in the confluence of two processes: changes in muscle protein turnover (protein synthesis and breakdown), and satellite cell function. In this presentation I will review the evidence summarizing what we know about changes in protein turnover that drive changes in muscle mass. Evidence for the impact of protein – dose, timing, and source – will be reviewed. In addition, the impact of the amino acid leucine, as a key amino acid in stimulating muscle protein synthesis (MPS), will also be examined. I will also address the role of external load and how motor unit recruitment is an independent variable determining muscle activation and muscle fibre hypertrophy. The role of what some call intensity, as a driver of MPS and muscle hypertrophy and strength gain will also be discussed. Finally, I will show evidence that demonstrates the belief-based, not evidence-based, role of endogenous hormones in stimulating MPS and hypertrophy. Attendees will gain up-to-date evidence-based knowledge on what is currently understood about the science of muscle protein turnover and exercise adaptations.