How does Helix calculate your Muscle Composition result?

Scientists have been trying to uncover a genetic explanation of muscle composition for a long time, since before the sequencing of the human genome. That is because scientists have known that skeletal muscles, like those in your legs, come in fast twitch and slow twitch types. The proportion of each type you have is determined at birth and stays fixed throughout your life.
In trying to understand what genetic factors determine that initial ratio (spoiler: we still don’t know!), a protein was identified that is only found in fast twitch muscles. This protein, made from the gene ACTN3, is important for helping muscles to contract. Scientists quickly noticed that some people didn’t make this protein because of a specific variant in the gene. This variant is called rs1815739, and the presence of a T results in a shortened protein that can’t help muscles contract in the same way.
Knowing this information, scientists started looking at a group of people where muscle composition is really important: elite athletes. They separated athletes into two groups, those who compete in power sports requiring speed and strength, and those who compete in endurance sports. What they found was that the power athletes almost always had the full ACTN3 protein.
Helix analyzes this same variant, rs1815739, to tell you about your muscle composition result. The TT result is more common in power athletes, but it doesn’t mean everyone who has TT is going to be an elite power athlete. In fact, this one genetic variant only influences your performance ability in a very small way, if at all. In reality, it’s a fun way to compare yourself to athletes—but remember that DNA isn’t destiny, and you should let your passions drive your choice of sport.