I would say that our knights would be massively strong, but not big. Harnesses show us that knights weren't beefcakes, but the act of repeated combat will toughen you up. For instance, I don't look impressively strong at all. There are a million football players that make me look small, but I'm stronger than most of them. Also, weightlifting builds muscle and was developed by bodybuilders. It's mostly bulk.
There are guys that can out lift me but they cannot actually do some of the things I can do. Most "weight training" I get is pushing 600lb bales of hay and things that involve no weights. I'm also good at projecting my strength, which means I can hit harder and throw around 150lb friends (or opponents) around like ragdolls, while technically stronger people cannot. I think knights might have been good at this also...
Knights would be very smiler. Not very big, but can project some serious force.
Also, tone is overrated. I beat the kids w/ washboard abs on the crunch machine all day. Studies have shown that having extreme tone is in fact not ideal for activities knights would do. Your body needs something to feed on when your food energy is gone. That's how you lose weight. If you don't have this "buffer" your body will begin to cannibalize itself. Starting with the muscles. So for prolonged extremely strenuous activities (battle) it's actually decremental to be wickedly toned. The only reason modern marathon runners and such do not do this is because they can accurately predict what the activity is going to be, energy used, and eat accordingly. When your armies encamped in enemy territory, and you don't even know if the enemy will give you a chance to get breakfast, you better have some reserve source of energy.