What role does ACTN3 play in fatigue?

The provided context contains no direct information about ACTN3 and its role in fatigue. In general scientific knowledge, ACTN3 (alpha-actinin-3) is a gene encoding a protein expressed in fast-twitch muscle fibers. A common loss-of-function variant (R577X) results in absence of the protein. Some studies suggest that carriers of the X allele may have lower sprint and power performance but potentially better endurance and fatigue resistance. However, evidence is mixed: meta-analyses show small, inconsistent effect sizes. The influence on everyday fatigue is not established. Without context-specific studies, the evidence level is unclear. Consumers should not overinterpret ACTN3 genetic test results; they are probabilistic and should complement, not replace, professional athletic or medical advice.