This interval workout is not suggested for beginners unless modified (see Figures 1 and 2). Consult with a physi- cian, physical therapist, or other trained health or exercise professional before using the exercises. People with cardio- vascular diseases or other metabolic risk factors (e.g., high cholesterol or diabetes) should be cleared for vigorous exercise by a physician. A preprogram land-based ramp assessment is also recommended for those who are consid- ered high risk. Other general guidelines include:
• Before beginning high-intensity inter- vals, you should be able to exercise for at least 20–30 minutes at 70–85% of maximal heart rate (moderate to hard), without exhaus- tion or problems.
• Build gradually. You may need 8–12 weeks of training aerobic endurance before starting high-intensity inter- vals. Begin with an interval workout one day a week and add intervals to regular workouts over time.
•The day after interval training should be only light exercise or recovery.
•Always warm up and cool down (5–10 minutes each).
• Use the perception of effort guide or a heart rate monitor to check intensity during the workout. With a heart rate monitor, you can record your aver- age workout heart rate and enter the data into a Web-based converter that estimates calories expended (www. shapesense.com/fitness-exercise/ calculators/heart-rate-based-calorie- burn-calculator.aspx).
• If your heart rate does not drop to ~50–70% of maximal heart rate (HRmax) during recovery intervals, shorten your work intervals and/or lengthen recovery intervals.