After a long engineering career and many hours spent sitting on the crapper reading technical magazines, I have discovered the cause for and solution to numb legs after reading a couple good articles.
The numbness comes from your arms/elbows crushing the main blood vessles in your legs as you lean on them whilst perusing the latest EETimes, RF Design or Microwave Journal. The longer you sit there, the more numb your legs get, and the less likely it is that you'll even be able to walk after standing up. Trust me, I've been there.
There are two possible solutions. 1) Do not lean on your legs when reading, or 2) get high tech. Believe it or not, I have a piece of 1/4" thick plywood that is cut about 3 inches wide and 15 inches long that I carry into the can to lay atop my legs near the knees. Leaning on that wood distributes the weight across a much greater area, and that reduces the crush factor enough to permit indefinite reading periods. It's miraculous!
Hey, no need to thank me. Just "giving back" to the community that has been so good to me.