Thank you for sharing your story here. I feel like my brain kept going back and forth on this a bit. In general, recovery from workouts is just as important as the workout itself, sometimes even more important, so my first reaction when I read the headline was, "oh no, not a good idea." If I had someone, a client or friend or anyone, tell me they worked out twice a day, I would immediately assume they had exercise addiction, which can definitely be harmful and pathological. You made a good point in the end though, that a challenge is a challenge because it isn't sustainable in the long term. So true. I'm glad you gave your knees a break when they began hurting though! Good job on listening to your body while still standing up to the challenge!