Glycine or creatine: which is better for recovery and muscles?
For muscle building and recovery, creatine has considerably more evidence behind it than glycine, about which the available studies say nothing. Creatine is safe at normal doses and works best for short, explosive exercise.
Creatine has the strongest support for both muscle building and recovery. Many studies combined conclude that it increases lean body mass, muscle strength, and performance during short bouts of intense exercise. It is one of the most thoroughly studied supplements in sports science.
When it comes to recovery after hard exercise, creatine lowers blood levels of creatine kinase, a marker of muscle damage, by an average of around 31 units compared with a dummy supplement. That effect was measurable up to 96 hours after exercise. A smaller study of 40 participants also found that muscle strength returned noticeably faster in people taking creatine, and that they experienced less muscle stiffness and fatigue. That study was partly funded by a pharmaceutical company, but the authors state this had no influence on the results. For another marker of muscle damage, lactate dehydrogenase, the picture was mixed: only at 48 hours after exercise was there a clear reduction; overall there was not.
A notable difference between the sexes was found: women had less swelling after exercise when using creatine, while that effect was not visible in men. This is a small finding that deserves further research, but it suggests that women may benefit particularly from creatine for recovery.
For combat sports athletes, creatine is effective for explosive strength and power, especially during short, high-intensity efforts. In programmes lasting 6 weeks or longer, lean body mass also increases. One drawback: creatine raises body weight, which can be a problem for athletes who need to meet a weight category. For endurance, recovery, and fatigue in combat sports athletes, the supplement showed no measurable effect.
Glycine as a standalone supplement for recovery or muscle building was not examined in the studies provided. Nothing can therefore be said about it based on the available sources. Anyone choosing on the strength of current evidence should choose creatine. At controlled doses, no serious side effects have been reported in healthy athletes.
The evidence for creatine rests on several large reviews, including an overarching analysis that pulled together many reviews and many studies, supplemented by a study with randomly assigned participants (40 people) and focused reviews for combat sports and football. For glycine taken on its own, no studies were found in the sources provided; no conclusions about glycine can therefore be drawn. The researchers themselves point to variation across the recovery studies and an average risk of bias, so the recovery figures are a guide, not a firm answer.