Many people believe that they will be fit and healthier if they train intensely like professional athletes.  However, those athletes compete at a very high level, and their allostatic loads are specific to their sport. There is no need to work that intensely if you participate in recreational sports. Generally, I like to keep workouts at moderate levels. There are times when I keep intensities high. Examples are clients who want to lose weight within a short period of time, competitive athletes, or clients focusing on muscle hypertrophy. Those are the only times.  Most people train intensely yet do not recover appropriately. They have nutritional deficiencies that can lead to excessive protein catabolism. This is a big reason why we continually reassess to avoid overtraining. Your training load should be just enough to meet your functional requirements. Staying fit is about getting stronger, increasing flexibility and improving stamina.