FIRST AID/BLISTERS
Your body literally can get torn apart in races.
Sore, blistered feet, traumatic injury, infections, heat illness, muscle cramps/dehydration, disease and simply running out of steam all dramatically affect your (and your team's) performance.
Interestingly, heat illness, either hypothermia (too cold) or hyperthermia (too hot), ranks as the #1 reason people drop out of adventure races.
Ian Adamson - RW Guide to Adventure Racing