Why do i get nosebleeds with exercising?

Blood pressure?: Nosebleeds occur due to small superficial blood vessels in the front part of the nose. Increases in blood pressure can sometimes cause these blood vessels to open up especially the area around them has been traumatized. You should see and ear nose and throat doctor to have your nose looked at and cauterized.

Also, Dryness: In addition to the other items listed, your nose may be drying out. Make sure you are well hydrated before, during, and after exercise. You might also try a otc saline nasal spray to help moisturize the nose.