Evidence suggests that normal diurnal variations in testosterone and growth hormone do not play a significant role in muscle protein synthesis. A meta-analysis showed that men and women achieved similar increases in muscle with resistance training, despite men having higher testosterone levels.

While daily fluctuations in testosterone do not drive muscle protein synthesis, supraphysiological steroid doses are anabolic. Testosterone boosters come and go, but Dr. Phillips states they are ineffective, and it's better to focus on resistance exercise.

Growth hormone stimulates stature and collagenous tissue synthesis allowing tendons to become stronger. Dr. Phillips contends that excessive growth hormone may increase cancer risk, and one should exert caution. In this clip, Dr. Stuart Phillips discusses the implications of hormones in muscle mass growth and compares physiological to supraphysiological doses.