What Makes 'Physical Outliers' So Strong: Breaking Down Size, Genes, and Talent

In a cross-sectional study of 68 adults aged 18–30, people with a larger build (BMI) had greater absolute maximal strength on combined leg press and chest press (BMI vs. maximal strength, r=.49). But the star of the show isn't fat. Body weight correlated strongly with fat-free mass — muscle, bone, water minus the fat (r=.70–.80) — and that fat-free mass was what tracked with the weights lifted. So 'heavier people are stronger' because of the muscle that accumulates as the body grows larger (ten Hoor et al., 2018). Note that this is about absolute strength, a separate question from strength divided by body weight.

r=.49

BMI vs. absolute maximal strength

r=.70–.80

body weight vs. fat-free mass

Sumo wrestlers are the textbook case. Comparing 37 professional wrestlers, 14 bodybuilders, and 26 untrained men, the wrestlers' fat-free mass exceeded the bodybuilders'; six topped 100 kg, with a maximum of 121.3 kg (height 186 cm, weight 181 kg). Even though the wrestlers carried more body fat (26.1% vs. 10.9%), they still had more muscle and bone beneath it (Kondo et al., 1994). The same structure — more fat-free mass than the frame suggests — explains how a heavy-set comedian who recently went viral in Japan benched 100 kg on his first attempt. And the reason bears and wild boar are so powerful comes down, in the end, to sheer absolute muscle mass.

121.3 kg

highest fat-free mass among wrestlers

6 wrestlers

over 100 kg of fat-free mass

26.1%

wrestlers' mean body fat

Size, however, struggles to explain explosiveness. Enter the ACTN3 gene, which encodes alpha-actinin-3, a protein in fast-twitch fibers (they contract fast and hard but tire quickly). A meta-analysis pooling ~20,000 people found the R variant of this gene was somewhat more common in elite power athletes (odds ratio ≈1.20; more clearly in women at 1.58). Yet the effect size is small, and elite athletes turn up in every genotype (Tharabenjasin et al., 2019). The kind of burst that lets someone out-sprint a national record holder lives in this territory of predisposition — but no single gene decides it.

OR 1.20

R allele vs. elite power athletes (overall)

OR 1.58

same association in women

The other genetic thread is myostatin, a hormone that brakes muscle growth. When that brake is genetically ineffective, muscle develops to an extreme. Double-muscled Belgian Blue cattle and the beefy 'mighty mouse' are the classic examples, and in 2004 came a report of a human child who was strikingly muscular from birth, carrying a loss-of-function mutation in the MSTN gene (Schuelke et al., 2004). Part of why animals are biologically strong lives here. That said, this is a single case of an extremely rare mutation — worth stressing that it does not apply to ordinary people.

n=1

human case report (rare mutation)

To sum up, the making of a physical outlier is the overlap of a large fat-free mass and a genetic predisposition. But any single gene's effect is small, and how easily you build muscle — and the character of your fibers — is also shaped heavily by environment: how you train. Flip that around and the room to grow, for most people, lies not in a lucky roll of the dice but in patiently building an ample build (fat-free mass) through training and nutrition. Given that even a simple strength marker like grip strength is tied to future health, steadily adding your own fat-free mass tends to pay off more than envying the 'monsters.'