I've spent 20 years in various kitchens, pizza included, and in my experience while kitchen work is very tiring it's not very good exercise. In a well designed kitchen you will mostly be moving back and forth in a small, maybe 5 square foot, area bending over, squatting down, standing back up, and reaching a lot. Don't get me wrong, it is very active work, but it's not likely to make you much stronger or improve your cardiovascular health or conditioning much.

There's something else to consider as well. Relative to the misery, kitchen work pays very, very poorly. As a result kitchens are largely populated by those either unable or unwilling to find better paying and less demanding jobs or by those who are deeply passionate about the work. Neither of these types make terribly good workmates to a casual interloper and it would be wise to keep in mind that those around you are living out a tough life. One they mat find deeply rewarding, but tough nonetheless.

There are, however, as many types of kitchens as there are types of people, so you may find a place that fits with what you want to get out of it, it just might be a longer than average search. Good luck, though.