Most of us don't have the luxury - or more likely, the desire - to work out for hours on end. The idea is to get the most out of the time and energy we spend exercising in order to improve our fitness levels and reduce body fat. For those looking to improve cardiovascular fitness, doing the same thing on the bike, treadmill, rowing machine or elliptical trainer week after week doesn't work. That's because the body is amazing at adapting to workouts. The only way to make positive gains with cardio training is to continuously challenge the body with progressive workouts.
One way to vary workouts is by using the heart rate zones. In general, there are three zones: fat burning, cardiovascular or aerobic, and interval or anaerobic. By changing the workout zone, you're better able to prevent boredom and keep motivated. Also, research shows interval or anaerobic training raises the post-workout metabolism and keeps it up longer than steady state or aerobic exercise.
The first step is to determine what your maximum heart rate is. The most popular method is to use an age-predicted formula (that is, the Karvonen formula: 220 minus age). This technique is convenient to use but it's not as accurate as some other measurements. There can be a difference of plus or minus 15 beats per minute.
Another option is to determine your respiratory exchange ratio (RER). This measures the amount of carbon dioxide you produce and the amount of oxygen you take in. If you're inhaling more oxygen than exhaling carbon dioxide (that is, a ratio of 1:0), your body's able to meet fuel demands using a high per cent of fat. On the other hand, if the RER ratio is above 1:0, you're working at a very high intensity and are producing more carbon dioxide than taking in oxygen. However, measuring RER requires special equipment.
Once you know your maximum heart rate, by using percentages of this figure you can determine where your different training zones are. Typically, the fat-burning zone is between 60 and 65 per cent of your maximum heart rate, but recent studies have found the greatest fat oxidation occurs between 68 and 79 per cent. So if you're a 40-year-old male, to burn the highest per cent of fat calories, your heart rate would be 135 beats per minute (bpm). But this doesn't burn the most calories. The higher the intensity, the greater the number of calories burned up, but the smaller percentage of fat calories.
This brings us to the next category, the cardiovascular or aerobic training zone. Here, the heart rate is anywhere between 80 and 89 per cent of maximum heart rate. Before moving on to this higher intensity, it's best to be able to maintain 30 minutes of continuous exercise in the fat burning zone. Even when fit enough to do a tough workout, it's still a good idea to continue to do low-intensity workouts to maintain a good fitness base.