Interval training has taught us that to get the maximum benefit from every mile you run, you need to keep the intensity high and time working low. While this is a solid strategy for general fitness, it will never get you to the front of the pack for running. Research indicates that doing most of your running (about 80 percent) at low intensity (where talking is comfortable) can improve race times significantly more than running above the ventilator threshold more than half of the time. "We believe that the runners who did more running at low intensity were less tired for the high-intensity sessions and therefore got more benefit from them," says Jonathan Esteve-Lanao, an exercise scientist at the University of Madrid. The rule: Keep 80 percent of your runs easy and hit the rest of them hard. Here's a sample week.

Tuesday: Interval Run

  • 5-minute warm-up
  • 10 x (1 minute at 5K pace and 2 minutes easy), 5-minute cooldown

Thursday: Easy Run

  • 45 minutes easy

Friday: Lactate-Threshold Run

  • 5-minute warm-up
  • 30 minutes at half marathon race pace
  • 5 minutes easy

Sunday: Long Run

  • 1 hour 15 minutes easy