Day 4. You're only doing cardio. (Most CrossFitter won’t have this problem) Yes, cardio is important for calorie burning, but a proper exercise plan includes cardio, strength training and flexibility. If you're just doing cardio, then you will be burning calories and strengthening your cardiovascular system, but you won't be really changing your body composition by building more muscle. For that you need strength/resistance training! If you are doing strength/resistance training, but not pushing yourself or increasing the weights, staying in your comfort zone your body will never adapt or change.
Get-Results Remedy: DO CROSSFIT! Or Lift weights, do body-weight exercises, such as lunges and push-ups, at least twice a week to reap the amazing benefits of resistance training; including decreased body fat, increased muscle mass and stronger bone density.
The same could go for anyone who only does weight/strength training with no cardio, you need a good balance of both for the perfect around fitness, health and strength program.
CrossFitter’s are generally stronger Lbs for lbs than people who solely lift, got a high level of endurance, energy levels and CV endurance, good flexibility/mobility, with a better understanding of what real health and fitness is, performing movements with the correct form, understanding muscles and how they work, preventing injuries/illnesses, with body composition/aesthetics been a bi-product of enjoying your fitness and training program.