What causes a stitch?

Question

When your exercising and you receive a pain in your side. What is happening?

Answer 1

tight muscles and a lack of water.

Answer 2

It's a muscle cramp.  When you excercise & sweat a lot, you can become slightly dehydrated, which also causes you to lose electrolytes (i.e. salts, magnesium, potassium, etc.) which will definitely contribute to the cramping.  That's why they tell you drink sports drinks such as gatorade.  They don't contain a whole lot of electrolytes, but enough to help the average person working out.