The normal concentration of sodium in the blood plasma is 136-145 mM. Hyponatremia occurs when sodium falls below 130 mM. Plasma sodium levels of 125 mM or less are dangerous and can result in seizures and coma. Did I scare you? Good. Read on.

When you run, your body looses fluids. To run optimally, you need to replace the fluids your body looses. Your personal sweat rate (PSW) will help you determine how much you need to drink and how often while you are running. How to determine your sweat rate: