I don’t think people are physically stronger now than before. My great-grandfather, at the end of the 19th century, ran on the railway 17 kilometers in the morning and 17 kilometers in the evening, and the rest of the time he mowed the grass on hot days.
Reminds me of my dad, who used to mow a very large lawn with one of those mechanical push cutters. It was a constant load of work. As it was finished, it was almost time to start again.