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.
Maximum Heart Rate
HRmax is calculated by subtracting age from 220. The equation "220-age" yields an estimate only, since there is variability in maximum heart rates (see "Errors in Predicting Maximum Heart Rate" below). HRmax is biologically determined and declines as you age, and the correlation to age is strong; that is, if a large number of 20-75-year-old individuals walked on a treadmill to exhaustion to reach their HRmax, the distribution of heart rates would range from approximately 200 bpm (beats per minute) for the 20-year-olds down to 145 bpm for the 75-year-olds.
What Range Should I Train At?
Most people train within an aerobic exercise training zone (40% to 85% of HRmax). Aerobic capacity (endurance) will improve faster if you train closer to 85% than if you train at 65%, but some individuals don't have the capacity to start training at 85%, or they simply prefer to start training at lower values and gradually increase the intensity over the time. Some individuals may even need to start at levels as low as 40% or 50%, depending on their age, level of fitness, or body weight. But the level that you start at isn't all that relevant. What matters most is that you get started, and then over time, as your endurance improves, you can gradually increase the intensity.
The body accommodates to both low- and high-intensity workouts by increasing the activity of respiratory enzymes and other biochemical reactions in the muscles. Anaerobic training-like intervals and speed work are helpful if you want to improve your time or perform optimally in an event like a 10K run or a 50-mile bike ride because the training prepares your body for the specific anaerobic demands of the event (like when you have to sprint or climb a hill). This type of training, called "specificity of training," is effective because it mimics the type of exertion experienced during the event.
On the other hand, if health and general levels of fitness are the goal, and not performance in a road race, then there's no need to train anaerobically unless you like to push. Instead, substantial gains in health and fitness can be accrued by aerobic training between 40% and 85% of HRmax. Volumes of research prove this.
A traditional method of aerobic training is to start at the low end of the aerobic training range, say 50% or 60%, and as training continues and the heart and muscles adapt to the challenge, the intensity is progressively increased. For example, a sedentary individual might start at 60% of HRmax and remain at that level for four weeks, and then during the fifth week increase the intensity to 65% (increases of 10% of intensity and/or duration is the standard recommendation). Again, the body accommodates to the work over time, and when higher levels of fitness are desired, the intensity needs to be increased. Training heart rate zones offer a quantifiable method of guiding workouts and determining exercise intensity.