Most of the male skeletons in graves I study from early medieval England show a few common signs of heavy physical exertion:

• Back problems from heavy lifting (including osteoarthritis, slipped disks, and several different kinds of weight-lifting injuries), often by the mid 20s
• various kinds of deformities or injuries from lifting too much, too young (putting the body through strain while it was still developing)
• degenerative joint disease from damaging joints that were unable to properly heal
• Robust bones strengthened from heavy lifting

All of these conditions show that early medieval men put their body through heavy stresses from manual labo that started young, and continued relentlessly until death. Your average man (who spent most of his life farming) must have had very good muscle tone.

But this came at the cost of longterm health. These aren't the skeletons of people who followed balanced exercise regimes. They're the bodies of people subjected to heavy labor from an early age, with the consequence that many would have been creaking like older men by the time their children were old enough to start pulling their share of the burden.

A 6th century man I looked at yesterday had:

• An injury to his glutes from lifting (squatting) poorly
• A broken, improperly healed toe from a farm accident
• A deformed shoulder from lifting too much at a young age
• A congenital back problem exacerbated by overwork, resulting in constant back pain

He died around the age of 30, and is pretty typical for an average-to-well-off country farmer.

Women have similar signs of stress, though they're more likely to have foot problems from squatting long hours (perhaps milling grain, or making textiles) than injuries from heavy lifting. Many women had neck problems from hunching over close work (like sewing or spinning).

It's much more common to see evidence of periodic hunger (hypoplasia, Harris lines) than of over eating. People were more likely to be hungry than fat.

Ordinary Romans had similarly hard lives, though I'm less familiar with their skeletal remains so I can't make a direct comparison. The Roman empire was built on an agrarian economy, and these farmers lived in similar conditions to those of the early middle ages (though perhaps skmewhat worse, as the Roman ecomony often focused so much on grain production that dietery diversity was restricted for peasant farmers, sometimes with adverse health effects).

This varies region by region, of course, but in general: when imagining Europeans of the past, picture farmers who are lean, strong, and active, but whose bodies show stresses of overwork, degenerative wear, and lots of aches and pains.