Aerobic Exercise for Weight Loss
Viewer question: I've heard that exercising at a lower heart rate burns more fat but fewer calories than exercising at a higher heart rate. Which form of exercise (slow or fast) will help me lose weight the fastest?
Author's response: At lower intensities of exercise, muscles burn a higher percentage of fat than carbohydrate, but not necessarily more total fat, or more total calories, than at higher intensities. This is a subtle distinction, but it's an important one. Here's some background to help understand why.
Aerobic exercise facts
- Aerobic exercise is sometimes known as "cardio"- exercise that requires pumping of oxygenated blood by the heart to deliver oxygen to working muscles.
- Aerobic exercise stimulates the heart rate and breathing rate to increase in a way that can be sustained for the exercise session. In contrast, anaerobic ("without oxygen") exercise is activity that causes you to be quickly out of breath, like sprinting or lifting a heavy weight.
- Examples of aerobic exercises include cardio machines, spinning, running, swimming, walking, hiking, aerobics classes, dancing, cross country skiing, and kickboxing. There are many other types.
- Aerobic exercises can become anaerobic exercises if performed at a level of intensity that is too high.
- Aerobic exercise not only improves fitness; it also has known benefits for both physical and emotional health.
- Aerobic exercise can help prevent or reduce the chance of developing some cancers, diabetes, depression, cardiovascular disease, and osteoporosis.
- An aerobic exercise plan should be simple, practical, and realistic. Specific equipment (such as cardio machines) may be used but is not necessary for successful aerobic exercise.
What is aerobic exercise?
Imagine that you're exercising. You're working up a sweat, you're breathing hard, your heart is thumping, blood is coursing through your vessels to deliver oxygen to the muscles to keep you moving, and you sustain the activity for more than just a few minutes. That's aerobic exercise (also known as "cardio" in gym lingo), which is any activity that you can sustain for more than just a few minutes while your heart, lungs, and muscles work overtime. In this article, I'll discuss the mechanisms of aerobic exercise: oxygen transport and consumption, the role of the heart and the muscles, the proven benefits of aerobic exercise, how much you need to do to reap the benefits, and more.
It all starts with breathing. The average healthy adult inhales and exhales about 7 to 8 liters of air per minute. Once you fill your lungs, the oxygen in the air (air contains approximately 20% oxygen) is filtered through small branches of tubes (called bronchioles) until it reaches the alveoli. The alveoli are microscopic sacs where oxygen diffuses (enters) into the blood. From there, it's a beeline direct to the heart.
Getting to the heart of it
The heart has four chambers that fill with blood and pump blood (two atria and two ventricles) and some very active coronary arteries. Because of all this action, the heart needs a fresh supply of oxygen, and as you just learned, the lungs provide it. Once the heart uses what it needs, it pumps the blood, the oxygen, and other nutrients out through the large left ventricle and through the circulatory system to all the organs, muscles, and tissues that need it.
A whole lot of pumping going on
Your heart beats approximately 60-80 times per minute at rest, 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime! Every beat of your heart sends a volume of blood (called stroke volume -- more about that later), along with oxygen and many other life-sustaining nutrients, circulating through your body. The average healthy adult heart pumps about 5 liters of blood per minute.
Oxygen consumption and muscles
All that oxygen being pumped by the blood is important. You may be familiar with the term "oxygen consumption." In science, it's labeled VO2, or volume of oxygen consumed. It's the amount of oxygen the muscles extract, or consume from the blood, and it's expressed as ml/kg/minute (milliliters per kilogram of body weight). Muscles are like engines that run on fuel (just like an automobile that runs on fuel); only our muscles use fat and carbohydrates instead of gasoline. Oxygen is a key player because, once inside the muscle, it's used to burn fat and carbohydrate for fuel to keep our engines running. The more efficient our muscles are at consuming oxygen, the more fuel we can burn, the more fit we are, and the longer we can exercise.