Glycine is a non-essential amino acid, which, in terms of chemical structure, is the simplest of all 20 amino acids commonly found in proteins. Although the body can synthesize it itself, it plays several specific and irreplaceable roles in an athlete's body. But does its supplementation have significance for sports performance?
Key Functions in Metabolism
Glycine is an essential building block for the synthesis of other substances that directly affect muscle energy metabolism:
- Creatine Synthesis: Glycine, along with arginine and methionine, is one of three amino acids necessary for the production of creatine in the body. Creatine is crucial for ATP regeneration during short, high-intensity efforts.
- Glutathione Synthesis: It also participates in the production of glutathione, one of the most important antioxidants in the body, which protects cells from oxidative stress.
- Conversion to Serine: Within metabolic pathways, glycine can be converted to the amino acid serine with the help of the enzyme serine hydroxymethyltransferase.
- Metabolic Cycles: Glycine features in complex metabolic pathways, where it collaborates with coenzymes derived from B vitamins (specifically PLP – vitamin B6).
Manufacturer Claims vs. Scientific Evidence
In the sports nutrition supplement segment, glycine is attributed with a range of positive effects on performance. Among the most common claims by manufacturers are:
- Increased synthesis of phosphocreatine.
- Improved sprinting performance.
- Increased maximum strength
These claims, however, are based on very weak foundations. The scientific reality is as follows:
- Methodologically Weak Studies: Early studies that suggested an increase in strength after glycine supplementation (or gelatin, which is rich in glycine) were conducted with insufficient control and poor design.
- Unconfirmed Effects: Current sports science considers the ergogenic (performance-enhancing) effects of isolated glycine supplementation to be unconfirmed.
Conclusion for Athletes
Although glycine is indispensable for the natural production of creatine and cell protection, its supplementation in the form of an isolated supplement demonstrably does not lead to better sports results. For athletes, it is more beneficial to focus on sufficient protein intake with a complete amino acid spectrum, which naturally contains glycine, or on direct creatine supplementation, if the goal is to increase strength and explosiveness.
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Information Sources
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Jeukendrup, A., & Gleeson, M. (2025). Sport nutrition (4th ed.). Human Kinetics.
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