Farm strength
Farm strength accumulates over years and years.
You get it by working everyday past the point of exhaustion while tending to your land and livestock. Muscles develop extreme stamina from this behavior and often do not bulk up.
As a result, folk with common-looking physique conceal superhuman strength.
Farmers like this do not have a gym membership. They don’t even need to exercise. The strength they have is sustained through their work. In other words, being strong is just part of what it means to be a farmer.
For the record, achieving farm strength is hard work. The hardest work. No one wants to be bad at something for months. No one wants to work when they don’t feel like it. But it’s a lifestyle when you push through those feelings.
In exchange for working at it day-by-day, a unique kind of strength will accumulate.