ACTN3
Alpha-actinin-3 gene
What it does
ACTN3 produces a protein found specifically in fast-twitch muscle fibres, the ones that generate rapid, forceful contractions used in sprinting and heavy lifting. The gene's activity shapes the balance of your muscle performance.
The variants that matter
A common variant switches the protein off. People with two working copies tend toward power and sprint performance, while those with two non-working copies, very common in many populations, lean toward endurance.
If you carry the notable variant
Carrying the non-working version does not stop you building strength, it means your natural lean may be toward endurance, and your training and expectations can be set accordingly rather than fighting your wiring.
Why it matters in India
The non-working variant is common across South Asian populations, which is part of why endurance-style training and progressive strength work often suit the regional physiology well.
The honest caveat. ACTN3 explains only a small slice of athletic performance. Training, nutrition, sleep, and consistency matter far more than any single gene. No variant here makes or breaks an athlete.