Bad ergonomics can destroy you body. Sitting all day doesn't guarantee that you won't be a broken physically.
I expect there are jobs that are "medium duty" that are actually health-enhancing. Somewhere between back-breaking labor and sedentary engineer.
Maybe being a mail carrier and walking most of the day.
- Wake up early -- not too many chances for late-night drinking then feeling bad about it.
- Walk a long way, whatever the weather. The post office supplied excellent waterproofs (this is Denmark).
- Walk up so many stairs. Many apartment buildings have the letter boxes in each apartment's door.
- Occasionally run away from a dog.