I read through an old thread on exercise and aerobic threshold, since I'm currently stuck lying down to OI and don't want to get all weak and such. And maybe so I can tell any doctors to bugger off if they get on my case for laying down all the time So I read the papers from Pacific Fatigue Lab. Basically the idea is to do very short bits (30 seconds) of non-aerobic (under 55% maximum heart rate) exercise to keep muscles functional, and maybe improve functionality as well. The first thing that I noticed (and experienced) was confusion over what anaerobic exercise is, as discussed in those documents. The problem is that the heart rate range for typical anaerobic exercise is above that of aerobic exercise, so it's not really possible to get your heart rate into that anaerobic range without first going into the aerobic range. But the advice is very clear about staying under 55% of max heart rate, so obviously they aren't talking about the anaerobic exercise stage that is at 80-90% of maximum heart rate. My impression is that they use "anaerobic" when they mean "sub-aerobic". So even though sprinting is an anaerobic activity, it requires raising the heart rate too high, so it's not what's being recommended for us. If lacking actual testing to show the limit you need to stay under, the general calculation for the limit is (220 ? age) x .55. So at the ripe old age of 33, I shouldn't be going over 103 beats per minute (220-33 = 187 max heart rate, and 187 x .55 = 103). This is a problem because just standing up currently sends my heart rate to something between 100 and 110. So it would seem that I shouldn't be standing up any more than is absolutely necessary. I need an activity that is somewhere between doing nothing (laying around) and doing too much (standing up) that benefits my muscles. I'm at 70-80 when laying down, and 85-95 when sitting up for a bit, so instead of being completely inactive, I can probably do some sub-aerobic activities while horizontal. But the difficulty is in finding activities that can be done in that position - even Pacific Fatigue Lab isn't very helpful on this point. The "stage 1" activities include step-ups, wall push-ups, modified chair dips, and toe raises. Aside from stretching and breathing exercises, which are listed for between real exercises, these all involve standing. So what are some sub-aerobic activities we can do for 30 seconds or less while lying down? I think my arms are doing okay due to my excessive typing, but I worry about my legs and abdomen.