It was mentioned earlier about the Cornish X being lazy... and they are.... but their mobility can be greatly improved with a few changes. When ours were tiny we placed them in a brooder with the food and water and lamp all in distant areas from each other. It forces them to move around a lot more. We also did something strange with out brooder (which they stay in for about 10 days or so) We built in a false floor in part of it, and dropped in a tub about 16x24x5" deep or so. We filled it about 1/2 full of a mix of sand and wood ash and place a chunk of wood on one end to act as a step in and out for them. We would sprinkle some crushed sunflower seeds and peanuts in it a couple times a day and sometimes would treat them by scattering in a handful of either dried or fresh meal worms.
Doing this with the sand tub helped keep them moving and encouraged them to scratch and forage. Now that they are out in the big coop with an attached run they rush outside as soon as we open their pop door in the morning and they often spend their whole day outside lounging in the sun, digging for scratch and generally just rolling from one area to another. We did have to put guardrails on the ramp for them, and we have food and water (again in opposite corners) out in their run. They are still pretty lazy, but not total sloths. And I think giving them scratch to look for helps slow down their eating some.
Doing this with the sand tub helped keep them moving and encouraged them to scratch and forage. Now that they are out in the big coop with an attached run they rush outside as soon as we open their pop door in the morning and they often spend their whole day outside lounging in the sun, digging for scratch and generally just rolling from one area to another. We did have to put guardrails on the ramp for them, and we have food and water (again in opposite corners) out in their run. They are still pretty lazy, but not total sloths. And I think giving them scratch to look for helps slow down their eating some.