Day 5 on the Master-Cleanse was my first day back to the gym. I took it easy (i.e. 20min on the eliptical machine at a low resistance and 10 mins walking uphill at a 3.5 on the treadmill. I also did about 30mins lower body weights at my usual moderate intensity). Day 6 I did 30 mins of moderate intensity spinning and upper body weights. Today, day 7, I'm sore and will proably go for a long walk. On both my gym days I was REALLY suprised at how much stamina I had. I felt really strong, focused, and energized the entire time! My suggestions is wait till after you first 3 or 4 days into the MC. Start out slow with exercise and you may find you're pushing yourself a lot harder than you thought possible.