We’ve all seem them; those charts on the cardio machines in gyms and those big posters on the wall talking about heart rate zones and how each zone does something different for you. Some of the lower zones being a “fat burning zone.” Somewhere on the chart it’ll also probably tell you that you can calculate your maximum heart rate by subtracting your age from 220. While there might be some validity to the chart, you can pretty much disregard the entire thing. No two people are exactly the same and while the 220 – Age formula can be used, it is not accurate when it comes to older adults, anybody overweight, anybody underweight, or special populations. Take for example, an older individual in good shape that’s in their mid 40’s with an active lifestyle. They will have a much healthier cardiovascular system compared to a sedentary individual in their 20’s that is overweight or untrained.
As previously mentioned, the charts will have different heart rate zones on them. These will typically have categories such as Red-Line Zone, Anaerobic Zone, Aerobic Zone, Weight Management Zone/Fat Burning Zone, and Healthy Heart Rate Zone. Now while there may be some correlation with heart rate and these zones, it does not mean that is exactly what you’re going to get. These terms and zones are over simplified and said in a way to attract attention. It is true that when training at a lower intensity, your body will use mostly fat as a fuel source. However that does not necessarily mean that your going to burn off all your body fat, especially if you are only going for a treadmill walk for 15 minutes within that zone. All your body is doing is using fat as a fuel source rather than protein or carbohydrates (note that there is a difference between body fat and fat sources from food). This is so because at this lower intensity, your body is not in high demand for fuel, so it uses fat for its main source of energy.
Fat has the most calories per gram but does take longer to digest and be converted into energy. So because the body isn’t in need of a lot of energy to be made as quickly as possible due to the lower intensity, the body will conserve and take the slower approach. This can be shown by testing a persons RER (Respiratory Exchange Ratio). By testing a persons RER, you are better able to show the ratio of oxygen being inhaled and the amount of carbon dioxide being expelled. This shows us what energy systems they are using and the intensity at which they are working at. As intensity in training increases, so will the ratio of carbon dioxide released and oxygen consumed. This means that higher intensities use mostly carbohydrates and lower intensities use fats. This is one of they that they had base their zones off of for the chart.
While using these lower intensities for cardio in an attempt to lose weight can help you to reach your goals, your sessions would have to be an hour long or more. However you can burn about the same amount of calories, if not more, by doing just 30 minutes of a higher intensity cardio. This is one of the reasons why HIIT (High Intensity Interval Training) has become so popular. It’s all about getting the most bang for your buck.
Now there are some physiological changes that can come from training at different intensities and for different durations; this comes due to our bodies amazing way of adapting and becoming more efficient at performing these various activities. That is another benefit that can come from training at high intensities and doing various types of workouts and changing things up. That’s why those people you see at the gym that always do the same thing, will fail to see the benefits after a while of doing it. Lets take for example a person that goes for a five mile run every day before getting ready for work. It’ll be good for them and they will see many benefits in the beginning, but once they get a month or two into this though, the effects of this stimulus will decrease because the body is adapting and now it requires very little energy to perform this task. So for this person it could be beneficial to go for a fast three mile run occasionally throughout the week or adding in other forms of high intensity training such as circuits. It is less time being spent running, but now at this higher intensity they are able to push themselves harder and will burn more calories per half hour compared to that low intensity five mile run.
When it comes to weight loss, it is all about calories in versus calories out. Training in the “Weight Management Zone” is not the secret to weight loss. It can definitely help and I encourage people to get in a lower intensity bout of cardio once or twice a week for recovery purposes. Some movement and exercise is better than no exercise. However the most calorie burning and benefits relating to weight loss will come from the higher intensity workouts. So don’t be afraid to get that heart rate up and keep moving. You be able to accomplish a lot more and in a short amount of time.
Edited By: Adriana Colon