This isn't in muscle tone in the sense of being out of shape (although I am) but in the clinical sense. One of the unexpected discoveries to come from my adventures at the OT was that my muscles' default resting state is rather more relaxed than is usual. This means I tend to flop and slouch, to lean on things or drape myself over them. It's also why I tend to drop things: my muscles underestimate how hard they have to grip to hold onto something.
This means I have a habit of leaning forwards when I'm typing, resting quite a lot of my weight on my elbows. I've taken to putting a cushion between myself and the table to minimise it, but even so I have quite a forward lean going on.
The problem is that now I'm getting sore elbows and patches of skin irritation from the pressure. As you can see, the pillow isn't really fixing anything, so I have to find another way around this.
When I'm not typing, I tend to sit on the couch, leaning back with my legs braced against the coffee table. This is overall more comfortable and my posture's better. But it's not very comfortable to type in that position because the keyboard's too low, so my wrists have to bend backwards unnaturally.