Sore throats when exercising can have two main causes. Nasal obstruction and acid reflux. Poor flow of air through the nose makes it harder to oxygenate especially during a workout.
We are inclined to open our mouths to breathe better, especially when we are out of shape. Though many of us who are in shape find it more comfortable to breathe through the mouth especially when the nose is not working properly. Mouth breathing, however, can make the throat dry and for some people the throat can feel sore as the dry air can be irritating. The mouth is meant to eat through and talk through, the nose is for breathing. We are born as obligate nose breathers and our nose is our air filter and air moisturizer.
Sore throats during exercise can also be caused by chronic acid reflux that you’re not aware of. Silent reflux can cause chronic sore throats, hoarseness and clearing of the throat. Working out soon before you digest your food can allow acid into the back of the throat as you jump up and down, this will cause pain in the throat. Many of us make thick protective mucous to coat the throat and protect from the acid but some of us don’t have enough and throat soreness is a result. Try waiting 3 hours after eating for your workout, cut down on highly acidic foods. If this is not enough you can try an OTC reflux pill 1 hour prior to exercise. If not improving then see your doctor.