Hello! Being able to brush a medical insurance card for fitness doesn't mean going to the gym doesn't cost money. The money in the medical insurance card is your money. Go to the gym and spend all the money in your card. If you need to swipe your card in case of illness, you will have no money and have to pay cash. Thanks for reading!
Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.