What role does ACTN3 play in stress?

The provided context does not contain direct evidence for a role of ACTN3 in stress. ACTN3 encodes alpha-actinin-3, a protein in fast-twitch muscle fibers. Its well-known association is with sprint vs. endurance performance (R577X polymorphism), not with psychological or physiological stress. Some mechanistic hypotheses (e.g., effects on muscle metabolism and stress hormones) exist, but robust human studies are lacking. MyBody-X is a wellness test, not a clinical diagnostic. Its relevance to stress is currently unclear. Evidence: mechanistic/speculative.