I read this answer on Quora, I don't do crossfit and have nothing against it..But I have been burned out and had adrenal gland problems..It takes many months and therapy to recover...here is a real example I love Crossfit. I did it for four years, starting in my late thirties, and was in the best shape of my life. I love that it got me out of bed every morning and energized me for the day. I’m a major night owl with a 25–26 hr body clock. I would not have believed you if you told me 10 yrs ago that I’d be getting up before 5 am four days a week to go to the gym, and that I would be happy about it. Normally, I would find it easier to stay up until 5 am than to get up at 5 am. (I HAVE THIS GENE: Are You A Night Owl? It May Be A Gene Mutation) I love that it motivates people to get fit. Not just fit, but super fit. For no other reason than because it’s fun and it feels amazing. It teaches us to forget about “losing weight” to look good, and to think more about what we’re physically capable of. We also find out that sometimes we actually look better after *gaining* weight: *muscle* weight. It's possible to weigh more but be slimmer because muscle is much denser than fat, so it takes up much less space at the same weight. The number on the scale means nothing without more information. Muscle also revs up our metabolism, so we can eat a lot more without gaining fat. For the first time in my life, I could eat a ton more food, not only without gaining fat, but while losing fat!! I love that it teaches all of us to let go of our egos and focus on the moment. (Cherie Nixon's answer to What is the slowest thing you've ever progressed in?) I love that the results of our hard work become so evident almost every day and every workout. I know I just told you in the link above that my progress was slow, but that’s only if I compare myself to others in Crossfit. For ME, my progress in my physical fitness was amazing. I love that it makes the connection between diet and health SO evident. Coming back to Crossfit after a week of vacation and eating a lot of crap was intimidating. Every barbell felt 10 lb heavier than it did before vacation. But I knew that I’d get back to my former level of fitness within a week of getting back on track. On the flip side, it was amazing how great I felt, how much energy I had, and how much easier the workouts became when I was stricter about sticking to whole foods. I love that it brought my shoulder issue to my attention. (And no, my shoulder issue is not the reason I stopped doing Crossfit.) Due to bad posture at my desk, I was very slowly heading towards major mobility issues in my neck and shoulders that would have caused problems when I’m older. If I hadn’t done Crossfit, I wouldn’t have discovered that until it was likely too late to change it. Crossfit brought the problem to my attention and motivated me to change it. I went to a great physiotherapist who showed me what was causing it, and what to do about it. (Cherie Nixon's answer to Physical Therapy: Why does my shoulder hurt when I play racket sports, and what should I do?) OK, so if I benefited so much from Crossfit and loved it so much, why did I choose not to do it anymore? After a few years of feeling more energetic from Crossfit, I noticed that I was starting to become less and less energetic. It used to be that working out in the morning energized me for the entire day. Then I started noticing that it only energized me until about dinner time. Awhile later, I noticed that I was exhausted by late afternoon. Then by mid-afternoon. Then by noon. This happened over the span of about 6 months, after no problems during my first three years of Crossfit. I knew I couldn’t be aging *that* quickly. A friend had warned me about what can happen if you work out too intensely without enough rest, but I didn’t really pay attention until I started having problems. She had recommended a book The Schwarzbein Principle: The Truth about Losing Weight, Being Healthy and Feeling Younger: Diana Schwarzbein, Nancy Deville: 9781558746800: Amazon.com: Books, so I decided to read it. It was written by an endocrinologist who also specialized in nutrition. I had been looking for someone like that all over the internet. I was excited to discover that she takes patients from all over the country and is within reasonable driving distance from me, so now she is helping me, too. It turns out that I was heading towards adrenal exhaustion, and was in the beginning stages of adrenal insufficiency. I had a lifetime of things that contributed to this, but driving myself to my limits doing Crossfit four times a week, while averaging about 6 hrs sleep/night, and eating low carb, were a terrible combination. I was tearing everything down without giving myself the rest or the nutrients to recover. So now, as part of my recovery plan, I’m taking what I call a super rest. I’m eating tons more carbs (whole food starchy carbs) than I used to, sleeping a lot more, and exercising a lot less than I used to. I’m not even allowed to do any aerobic exercise right now. My current exercise regime is limited to walking and doing light weights max once/week. I’ve gained a lot of fat weight unfortunately, but it’s for my health. My doctor says I have to let my hormones and adrenal glands recover first, then I will lose fat weight naturally, assuming I stick to my healthy eating regime. Unfortunately, Crossfit and a “super rest” regime are not compatible. PS - To be clear, Crossfit is great for most people, as long as they get lots of sleep and whole foods, including starchy carbs. Rest is important!!!