by chimojo » Mon May 05, 2008 4:43 pm
I have read this recommendation: 5 min for beginners, then add 5 min every 3 weeks. So, it is possible that this person was not ready for 20 min yet. Also, it could be a reaction from the exercise.
To narrow the possibilities, I would have them reduce to 5 min and see if this continues. If it does, then make sure it is not really numbness, which is a common symptom and not exactly legs falling asleep.