In my professional opinion avoid anything with “extreme challenge” in it or any other variation of it. As fitness professionals and fitness lovers we see it all over advertisements and social media egging you on to do the next 21 day or 90 day extreme challenge. If that is what gets you going by all means continue doing it and more power to you. But in my own personal and professional experience challenges will only lead to burn out, increased risk for injuries in the long term and potentially overtraining if you do it hard enough.
What you need instead is something that is sustainable where you can do for life. That is how health and fitness works. Improving your health isn’t a sprint it’s a marathon.
Charles Trinh MS, PES, CSCS, LMT