Hi Jonta,
try some uphill walking as Eric F suggests on this thread:
http://forums.deeperblue.net/static-...ut-needed.html. You will burn your legs much faster, than during the walk on flat ground.
I practice apnea walks on passive exhale, the easy part is a bit shorter for me. I do this practice instead of oxygen table and I think with good results. The only problem with apnea walks is that you can hurt yourself. I partially solved this problem that I sit down at the end of the walk and hold my breath for another 10-30s. I still don't know my limits, so I do it this way.
Regards,
Jiri B
