We do a lot of long hauls in our rig ... my wife does not drive (91 ft with a tag trailer is long, and when she does drive its obvious she oversteers it when I'm in the back trying to sleep so she's pretty much relegated to 225mph 1/4 mi at a time). Anyway, about every 30 minutes i let all of the air out of the driver's seat and do 50 reps of squats until my head hits the roof (not standing but a pretty good workout). Got to have it on cruise and have light traffic/good lanes, but it keeps the blood pumping (and helps you stay awake).
I used to have to fly a bunch of 8 hour flights and got very conscious of deep vein thrombosis from lack of leg blood circulation.