Daniel West, graduate student in the Department of Kinesiology at McMaster, and lead author in both studies, explained that many people, including experts, have been convinced for a long time that anabolic hormones are vital for muscle protein synthesis, a process that eventually leads to larger muscles.
"A popular mindset for weightlifters is that increased levels of hormones after exercise play a key role in building muscle. That is simply not the case."
First study - intense leg exercisesThe investigators set out to find out what the responses were to intense leg exercises - they studied both male and female adults. Even though they detected a 45-fold difference in testosterone level increase, they all managed to make new muscle protein at precisely the same rate.
Participants managed to make new muscle protein at the same rate, despite huge differences in testosterone levels
As muscle proteins eventually lead to muscle growth, their finding was an important one, the authors explained.
"While testosterone is definitely anabolic and promotes muscle growth in men and women at high doses, such as those used during steroid abuse, our findings show that naturally occurring levels of testosterone do not influence the rate of muscle protein synthesis."
Second study - Post-exercise hormonal responsesThe investigators had 56 male participants, aged from 18 to 30 years. They trained five days each week, for a total of 12 weeks. They analyzed their post-exercise hormonal responses.
Muscle mass gains ranged from negligible to over 12 pounds (about 5 kilograms). However, the scientists found no relationship between muscle growth and their levels of testosterone and growth hormone after exercise. In other words, muscle growth or strength increase were not linked to growth hormone or testosterone levels.
Muscle growth and strength increases were not associated with raised levels of testosterone or growth hormones after weight training
However, they did find a link between cortisol levels and muscle mass gains. This was surprising, because cortisol is supposed to have the opposite effect - it is thought to break down tissue and reduce protein synthesis.
Co-author, Professor Stuart Phillips, said:
"The idea that you can or should base entire exercise training programs on trying to manipulate testosterone or growth hormone levels is false. There is simply no evidence to support this concept."
Written by Christian Nordqvist