[dereg]

I disagree. Here's why. I used to work out quite a bit and, with the help of P90X, I got up to 170-175 pounds of lean weight. I maintained it for a while, but adverse life events, a huge workload, and a crappy diet made me lost most of the weight (and a lot of the muscle mass) that I put on before.

Since my weight tumbled to 145 lbs, I noticed a huge difference in my physical well being, especially in sedentary positions. My posture worsened, my back constantly ached, and I started to suffer from RSI. I've been using the same chair all the while, a Herman Miller Mirra.

So, from my experience, weight and muscle mass was a primary determinant of my sedentary well being. Believe me, I was putting a lot less stress on my spine when I was doing 48 pullups in a workout, vs 8 now. I'm slowly working my way back up, and the back pain from sitting has lessened.