Teeth hurt when exercising hard what could this be? what to do when exercising so they don't hurt?

You might knowingly : Be clenching your teeth hard....A mouth guard can solve this if that's the issue.

Mouthguard: You may be clenching your teeth while exercising. You might want to pick up an inexpensive no-boil mouthguard at a pharmacy to see if it gives y you any relief. If it does then you can have your dentist fabricate a professional one. Good luck.

U could have nerve : Root problem in your teeth. Any gum swelling, pus , dental caries that may cause it? I suspect more of a dental than medical issue get examined!

?TMJ: It might not actually be your teeth but your tm joint. This is the hinge joint of your jaw. When exercising sometimes without noticing one will tighten up jaw or bite down on teeth a little harder. Take note next time you exercise and see if this is happening. If so your dentist can make a devise to help with this. Sometimes just the awareness of it will help you to relax. If not still see dentist.

Bruxism (clenching): Some people clench down hard on their teeth when they are exercising, especially when weight lifting. If this is the case for you consider a bite plate for when you are exercising.