Know when to stop.
Credit: Greg Wood / AFP Getty Images

Cramping is common enough – if you feel a side stitch, or a sudden muscle contraction, slow down. Have a sip of Gatorade if it persists and ease back to your normal pace when it goes away. But if you have to change your gait – to favor a leg, avoid pain, or get through that cramp – it's probably an injury where you need to stop. Once you're limping or hopping, it's time to call it a day, rather than putting yourself on a months-long injury reserve.