In the last blog, I talked about why cardio is so much more than just getting your heart rate up. With all the advice about the intensity of cardiovascular exercise lately, let’s take a look at what happens when you exercise at different intensities so you can make a choice about the right level for your body.
Oxygen: Remember that when your body has the equipment to use oxygen, it can fuel your muscles in a more sustainable way. The more equipment, the wider the range of exercise intensities your body can handle without getting tired and needing to stop. If the equipment that uses oxygen to produce energy is lacking, your body will have to go back to using the short-acting, non-oxygen-requiring system for producing energy. So, when you reach a level of exercise where your body cannot keep up with the demand for more oxygen to produce energy, your body will shift to the energy-producing system that runs out quickly.
What you practice gets stronger: This is why someone who does not move for extended periods of time will very often get tired faster, whereas a regular exerciser who has built up the equipment needed to use that aerobic system can last for a long time. Your body is a use it to keep it system. Like any good system, when one part is not working well, another part will pick up the slack in order to keep the system working. When it comes to the cardiovascular system, even if you have a disease that limits one part of that system, other parts will adapt—as long as they get the signals to do so. Cardiovascular exercise signals the whole system to get stronger in any way it can. This is why someone with lung disease or heart disease is especially in need of cardiovascular exercise, to signal the rest of the system to pick up the slack. When the heart or lungs don’t work as well, the muscles will compensate by building more equipment so they can use oxygen more effectively.
Carbon dioxide: If, during a cardiovascular exercise, you kick it up to a higher intensity, your breathing will reach an uncomfortable level. This is not your body wanting more oxygen—it is your body trying to get rid of carbon dioxide, the byproduct of the non-oxygen-using fuel system. That uncomfortable shortness of breath is called the ‘anaerobic threshold’. It is a sure sign your body won’t last much longer unless you lower the intensity.
Breathing vs. heart rate: This is why your breathing gives you a better idea about the function of your cardiovascular system than heart rate does. You can sense it, without having to measure it. Plus, without taking a special test to measure your maximal heart rate, your exercise heart rate range can only be predicted (and not very accurately). Your breathing level, however, is a real-time measure of what is happening in your body. The ‘comfort’ of your breathing lets you know if you have the equipment needed keep fueling muscles. When you are breathing uncomfortably, it is a sign the system is not prepared to keep up and your body is relying more on the non-oxygen, short-lasting fuel system.
Building stamina is possible for any body: For someone who is very fit, this happens at a much higher intensity. For someone who has not built up the oxygen-using system equipment, this happens at a much lower level. For anyone, though, when you exercise regularly, your body adapts by building more equipment for the oxygen-using fuel system, because it is a much more efficient way to fuel your muscles.
“Cardio” or “weight loss”: If you are looking to burn more calories and fat because you want to lose weight, don’t get side-tracked by trying to decide if you should do the cardio program or the weight loss program on your treadmill. Yes, your body uses more carbs at high intensity and fats at lower intensity, but in the end it really does not matter. Your body will break down fats to replace the carbohydrate (glucose) stores when you are resting after exercise. You don’t need to choose between getting more cardio or burning more fat. It’s all good.
The fine bottom line: What is more important for weight loss as well as overall fitness and health is how consistently you do cardio. Remember, after about three days of not doing cardio, the ‘equipment’ starts to get rusty. That’s why it’s important to consider how your brain perceives the exercise too. Your brain is hardwired to avoid what is uncomfortable. If you push the intensity to ‘get a better workout’ and are wishing every minute away, your brain is much less likely to want to go back and do that again—and there goes consistency.
That, my friends, is the fine bottom line of cardio. Do cardio at a moderate to motivating challenge for your breathing. Each time be sure it is the intensity level that feels good physically and mentally, so your brain wants to exercise again. Some days the motivating challenge is just getting started and enjoying a moderate intensity. Some days it could be a higher intensity because it feels good to push a bit harder. But on all days, if you are going to get the health and well-being benefits, it needs to feel motivating, not uncomfortable.