If you sit for most of the day and you run for one or two hours, you are a sedimentary person and an athlete, but sadly not healthy.
Both extreme are unhealthy, and you are probably going to develope two different sets of injury from both behaviours.
You are going to get the usual degeneration cause by sitting like: bad posture, osteoarthritis, sciatica etc. And probably some injuries from your high exercise load, like: tendonitis, shin splints, ligament tears etc.
Human body's don't need exercise they need movement, there is a huge difference between the two. Exercise is done for the sole purpose of exercising, like doing twenty squats in a row. Movement has a secondary purpose, for example I am going to hinge from the hips to pickup something from the floor.
When you move the intensity, frequency and the variety of movements you do is different. Compared with doing reps and sets.
Think of exercise like a nutritional supplement, it is a concentrated, isolated source of something you need within the context with everything else. This makes it incredibly easy to get to much, the same way it is easy to overdose on a vitamin supplement.
So you should treat exercise the same way you treat nutritional supplement, you should try to take as much of the nutrition from the food you eat and supplement as least as possible only if is close to impossible to get a certain nutrient from your diet.
Exercise is healthy in small quantities and detrimental in large quantities. There are several trends of exercise that seem a little excessive to me. Like running marathons and ultra marathons, CrossFit, body building etc.
Sadly these are perceived by the public as health promoting. High loads of exercise are definitely unhealthy as they increase your risk of injury.
As far as I am concerned if you are an adult, you can do whatever you want for as long you are not hurting anyone else. You can smoke, drink alcohol or run a marathon. But of course these things are not good for you.
I don't necessarily think that you shouldn't exercise at all, exercise is great at rehabilitating certain parts of your body. Like the stretch that I recommend.
Also modern life with all the convenience, underutilises the human body. Which could cause it to break down, like a car that you keep parked in your garage for a long period of time.
So there are two other forms of exercise that I think are necessary for modern humans.
Walking and some resistance exercise.
