Heart Rate Training Zone
It seems as though the concept of a heart rate training zone has been around forever. But I wonder how many people really understand how it works. In this article, I discuss the concept and how to determine your own zone.
The Main Idea
A heart rate training zone is a range that defines the upper and lower limits of training intensities. It is calculated using an age-related predicted maximum heart rate (HRmax) and a special equation called heart rate reserve (see "Calculating a Target Heart Rate Zone" below). The values are expressed as a percentage of maximum heart rate (for example, 70% of HRmax), and the range is based on (1) metabolic systems in your body that fuel your muscles during exercise, and (2) how hard you want to train. Training from 40% to 85% of HRmax is aerobic exercise ("cardio"). Aerobic means "with oxygen." Training above 85% of HRmax is anaerobic exercise. Anaerobic means "without oxygen."
The primary fuel during aerobic and anaerobic training is fat and carbohydrate, respectively, but it is very important to understand that both fuels are burned simultaneously at virtually all levels of exercise; it is not just one fuel or the other, except at the very highest intensities (close to 100% of HRmax). Resistance exercise and sprinting are examples of anaerobic training, whereas walking and jogging are typically considered aerobic, although you could walk or jog fast enough to make it anaerobic. It's likely that you are working anaerobically (above 85%) if you're out of breath during a workout and working aerobically (less than 85%) if you're only slightly out of breath.