What to watch with ACTN3 and Sport?

The ACTN3 R577X polymorphism (rs1815739) is the most studied genetic marker for sprint/power performance. RR genotype carriers (functional alpha-actinin-3) have advantages in explosive movements, while XX carriers (null allele) are overrepresented in endurance athletes. What to watch: XX individuals show higher risk of muscle injury and slower recovery after eccentric exercise. RR individuals may also experience muscle strains if training is not properly managed. Evidence for performance associations is strong (human studies), but for injury risk it is moderate. Important: ACTN3 is only one factor – diet, training status, and other genes (e.g., ACE) also matter. A genetic test alone cannot replace sports medicine advice. For XX genotype, consider adjusted strength training and adequate recovery. The clinical utility for everyday training is limited due to small effect sizes.