How do airline pilots relieve the physical stress and discomfort of sitting for long periods of time? Airline pilots are required to sit in the cockpit for quite a considerable amount of time during their day. For example, during the preflight, climb and descend portions of the flight, there are many events going on in the cockpit that requires both pilots' attention. The amount of time they are required to spend sitting in the cockpit is, surely, longer than that of a passenger on the same flight.

How do they relieve the physical stress/discomfort and other physiological issues associated with sitting for a long time? For example, during cruise, is it normal for one of the pilots to unbuckle the seatbelt, get up and stretch his legs in the cockpit? Do they do some simple exercise for a few minutes during the turn around?

Note: This question is not about how pilots deal with the mental stress of boredom in a long flight. This is about how they deal with the physiological discomfort associated with remaining in the sitting position for a long time.
I was on an EMB-145. The longest flight we usually had were 3.5 hours so my experience doesn't compare to Trans Pacific routes. As a crew-member I could get up to use the restroom, but there wasn't enough room to stand on the flight deck. You learn to sit different ways (one leg under you) to makes adjustments. Then the other leg under you later and so one. Some sort of seat Yoga I guess you could call it. My strategy was to walk, walk, walk, and stay off the plane as long as I could between turns. Your body adapts to the environment after awhile regardless of your body being in great shape or not.