Day 11

Fitter, Faster Short bouts of challenging aerobic exercise and brief periods of less difficult "recovery" work--boosts calorie burn and improves cardiovascular strength.

Interval Training--alternating short bouts of challenging aerobic exercise and brief periods of less difficult "recovery" work--boosts calorie burn and improves cardiovascular strength. New research in the Journal of Applied Physiology indicates that it may take even less time to get significant results: as little as six minutes of intense exercise three times a week (plus rest and recovery time).

At first, moderately active men and women who cycled at 80 percent of their maximal aerobic capacity fatigued after 26 minutes. But after performing three short sprint sessions a week for two weeks, it took an average of 51 minutes to reach the same point of fatigue. Their endurance levels nearly doubled--results that would require hours of lower-intensity exercise.

Because you work at such a challenging pace, even for a minimal amount of time, your body learns to work harder and your muscles adapt and get stronger. To boost your endurance, try the program outlined below three days a week for two weeks. Stick to low-impact activities to reduce your risk of injury.

Action	Duration	Effort Level
Warm-up	2 minutes	Easy
Sprint interval	30 seconds	Maximum, all-out effort using strong resistance
Recovery	4 minutes	Easy, using no resistance (or stop completely)

Repeat interval and recovery 4 to 6 times total.
Total time: 20 to 29 minutes