If you think of Classical Greek sculpture, which operated as a gold standard for beauty for so long, you tend not to have strain. Muscles register the distribution of weight, tension, but not strain.
There's a bit in Gombrich's Story of Art book where he contrasts an Italian and a German rennassaince self portrait and remarks disparagingly on the latter's "self conscious intensity" i.e a kind of strain and more generally what happens as the rennassiance moves north out of the warm Mediterranean climate is that ugliness appears, not just because the people are uglier, but because they strain against their environment, by necessity.