As an Internal Medicine Physician, the benefits of exercise are, of course, unquestionable. Having said that, there is now some evidence that one can overexercise especially as we all get older. I could show you quite a few studies that document this. Here is one study that suggests that there is a significant population of people that are "overexercisers" that have a higher risk of morbidity and mortality. This has been called the "J curve" of exercise that compares health status with different levels and intensity of exercise. This frequently shows that health improves with low and moderate exercise but then the mortality curve goes up with longer more intense chronic exercise especially after age 50. It has been hard though to clearly define what this more dangerous level of overexercise is.
I have been surprised how often I have seen this clinically with patients like marathon runners that presented with atrial fibrillation (an abnormal, often chronic heart rhythm problem that raises mortality) at relatively young ages. This study shows more atherosclerosis (hardening of the arteries) in marathon runners compared to people that don't exercise at all.
https://www.mayoclinicproceedings.or...14)00638-7/pdf
I am now 62 years old and have done power based interval workouts, races, century rides, etc. for at least 20 years. Now in my 60's, I have cut out the more intense intervals and don't pay much attention to my power meter anymore. I typically ride an hour or so daily and use the hills on my rides for my intervals. I usually ride at moderate aerobic levels to maintain good fitness but without overstressing my heart and body. I think there is some pretty good evidence to support this. Honestly, it has also made my cycling more enjoyable as I have gotten older.