The 10 Minute Rule

Start every run with 10 minutes of walking and slow running, and do the same to cool down. A warmup prepares your body for exercise by gradually increasing blood flow and raising core muscle temperature, says Jerry Napp, a Tampa Bay running coach. The cooldown may be even more important. Stopping abruptly can cause leg cramps, nausea, dizziness, or fainting. The Exception It takes less than 10 minutes to rev up on warm days.