The weightlessness experienced by astronauts is fun, but it is not without consequence.
The human body was designed for lazyness. That is why it takes so little effort to be overweight, but it takes effort to stay slim. When you don't exercise, muscle is replaced with fat, and bones grow thinner.
A regular person living in 1g will at least put their legs' bones and muscles to work a little whenever walking around, and their arms muscles and bones when doing things like using forks, knives or hashi for eating. In space, the lack of weight makes these activities so much easier, so the muscles and bones get less stress. In response, they grow weaker. And it's not just the limbs. The heart and lungs start getting lazy too.
From the ESA site for kids, on bone loss:
Space research is helping scientists to understand what happens and to find a way to combat the problem.
One method is to use volunteers who stay in bed for many weeks. These bed rest studies show how bones change when no weight is being put on them.
I've been emailing them for years now, volunteering myself. I could to that in a home-office setting even.
Anyway, exercising in space helps the body stay in shape, and helps avoiding osteoporosis. If your miners do go under 1g for most of the day, then they should be getting more stress on their muscles and bones than an astronaut at ISS would. They should not need to exercise in order to avoid weightlessness related problems. They should exercise, anyway, because it takes more than just an apple a day to keep the doctor away.