20 minutes total training time

Interval training can be a very effective and efficient means for achieving higher levels of cardiovascular fitness. It presents almost unlimited variations with respect to the exercise protocol, and provides a more interesting workout than standard steady-pace training. Because interval training can be more physically demanding than even-paced exercise, be sure to check with your physician before giving it a try. You may also want to consult with a personal trainer or fitness instructor to design an appropriate interval training program for your present level of cardiovascular fitness.

Wayne L. Westcott, Ph.D., is Fitness Research Director at the South Shore YMCA in Quincy, MA., and author of several books on fitness including Building Strength and Stamina, and his most recent publication, Strength Training Past 50.