Did you know DNA affects your muscle strength?

Feats of strength - The ACVR1B gene and growing muscles

From the very beginning of our existence, humans have been intrigued by strength. We have always been driven to test each other’s strength during feats of physical prowess, from the Highland games, to the Olympics. Strength athletics or strongman competitions have an ancient heritage, and are designed to truly test the strength of its participants. For instance, vehicle pull, keg toss, log throw and power stairs are only a few of the many events one will need to master if they want to become the World’s Strongest Man.

As you watch Edward Hall, the current World’s Strongest Man, deadlift the weight of a polar bear (500kg) or Big Z (Zydrunas Savickas) log press 228kg, you can’t help but wonder just how these ‘super’ humans can achieve feats of almost mythological proportions. Any one of them will attribute their success to hard work, discipline and determination, but there’s a possibility that genetics set these strongest men and women apart from the rest of us. Indeed, studies show genes can influence both muscle strength and power. For example, inheriting a specific version of the ACVR1B gene helps explain differences in muscle strength.

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With muscle, bigger doesn’t always mean stronger, because muscle strength has everything to do with the type of exercise we perform to make them grow. You grow muscles using a process called hypertrophy in two ways: You can increase the size of individual muscle cells, or you can increase the size of muscle fibres. Athletes, like strongmen, who train to lift heavy loads gain muscle strength because these types of exercises increase the size of muscle fibre, whereas the kinds of training bodybuilders use, multiple repetitions at submaximal weights, increases the size of their muscle cells to build bigger muscles. These muscles are more toned or defined but are not necessarily stronger.

The growth of our skeletal muscles is controlled by a protein called myostatin. Myostatin is a myokine, a messenger molecule used by muscles cells to talk to each other, and it inhibits muscle growth. Once released by muscle cells, myostatin binds receptor proteins found on the surface of neighbouring cells. The ACRV1B gene is linked to muscle strength and encodes one of these receptors, (activin receptor 1B). One variant of ACRV1B, rs2854464, is linked to knee muscle strength. People who carry the altered version of the ACRV1B gene are ~2% stronger than their peers with the normal version of the gene.

In another study, the altered version was found to be over represented in sprint/power athletes compared to endurance athletes and non-athletes. However, this finding was limited to a athletes of Caucasian-descent, and did not occur in a study of Brazilian athletes, suggesting the link between ACRV1B and athletic performance is ethnicity-dependent. Exactly how this version of ACRV1B affects muscle strength hasn’t been determined yet, given both myostatin and myostatin receptor levels are reduced following exercises promoting muscle growth, it’s possible changes in ACVR1B protein levels may explain the link.

Strong muscles have been linked to strong joints, strong bones and even better brain function. However, one thing to remember is that great feats of strength can often come from people we consider to be average or nondescript. Superman may have superhuman strength, but under his red and blue spandex, he’s just your average sized Clark Kent.

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