I am 185cm tall and not so flexible. I sometimes have to sit for prolonged periods of time (~1 hour or more) on the floor to use a low table, e.g. to eat or use a computer. It typically hurts my legs and back. How can I sit ergonomically on the floor when using a low table?
There are a few tricks which can make the cross-legged position comfortable:
- Sitting more "crossy" - if you are not flexible enough to align your heels one in front of another, cross your ankles or even cross your shins.
- Elevate the hips above your knees (by using a cushion, blanket or yoga-block)
- Support your knees (again using cushions or something similar).
These "tricks" come from yoga practitioners:
If you choose to sit cross-legged, it is important to have your knees level with or below your hips. If you are having difficulty maintaining an erect spine while sitting cross-legged, begin by sitting on the edge of a cushion, bolster, or rolled blanket. For additional support, place rolled blankets or bolsters under your knees. (You may find that with the knees supported, the inner groins relax and that when you take the supports away, your knees drop further easily.)
You can see this demonstration video
Apart from this, when you feel physical strain, a good idea is to make a break and stand up for a few minutes. This doesn't apply just to sitting on the floor, by the way, because sitting for a long time (regardless of the position) is connected with health risks and some experts recommend a break from sitting every 30 minutes.
I don't have references for this part: the pain you are feeling might be caused by low flexibility (especially in the hips), but also week abdominal and paravertebral muscles (both of which are important for a good, straight-back posture). Working on these issues over time might help, but, as with any exercise program, you need to be aware of your general health and whether you have any specific health issues, so that you can exercise safely.