• 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 average 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.