Nothing stops you from standing up, getting out of your seat and walk around the cabin every hour or so. I would even call this practice a necessity for your own, and thus your crew' and passenger's health and wellbeing.
Since locked cockpit doors all the airlines I've flown for this is an absolute No NO. So forget about crew's well-being. No sure how the pilot strolling around then cabin helps with pax well-being. The captain strolling around the cabin on long-haul flights and shaking hands with all and sundry has been a thing of the past for many years in the EU world and USA I suspect.
Amazingly, speaking to mates in various airlines, a B737 crew can do Canaries - Scandinavia up and back with only 2 pilots locked in their box for >6.00hrs before a very short leg stretch and then a repeat performance. Same is true for flights from N.Europe to Egypt or Gambia. Meanwhile a long-haul carrier from the national carriers, with an a/c designed for the job and thus large cockpit, does a 12.00hr single sector with 3 pilots and bunks, even down to S.Africa with no time change. Go figure.