The body is complex. Try not to box its functioning into simplistic principles like "it's not moving". Zen practice, for example, involves sitting as still as y

The body is complex. Try not to box its functioning into simplistic principles like "it's not moving". Zen practice, for example, involves sitting as still as you can for 25 mins at a stretch, followed by a meditation walk for a few minutes and then resuming. A retreat (called "sesshin") will typically involve such sitting for about 8-9 hours a day, for 4 days to a week. Monks have been doing this for a couple of millennia at the very least if you consider only Buddhism. In other traditions, monks may sit continuously for far longer than the 25 mins characteristic of current traditions. No longitudinal study of postures can top that record. The sitting posture matters because the spine is kept erect naturally, like a vertical pendulum. Once you get used to it, it is a pretty relaxed posture that feels quite sustainable .. compared to sitting in any chair.