Your Brain Might be Telling You One Thing, but Your Body is Saying Something Different
Most people think they know what aerobic means, or so they say. When asked, many associate it with breathing, air, or oxygen. Or they confuse it with “cardio” at the gym, where you can also find aerobic dance classes and pool aerobics. In fact, aerobics is a relatively recent form of exercise. It’s not even 50 years old, although humans have been doing it for millions of years. In the late sixties, Dr. Kenneth H. Cooper, an exercise physiologist for the San Antonio Air Force Hospital, Texas, coined the term ‘aerobics’ to describe the system of exercise that he devised to help prevent coronary artery disease. Dr. Cooper originally formulated aerobic exercises specifically for astronauts, but soon realized that the same set of exercises such jogging, running, walking and biking are useful for the general public as well, especially those suffering from being overweight, who are more likely to develop various heart diseases. He put together all of the aspects and methods he founded in his book Aerobics, which came out in 1968 and became an immediate national bestseller.
And what about anaerobic? What does this term mean? Being out of breath after short, intense and hard activity? Sprinting 100 yards on the track, going full-speed across the length of the pool, doing pushups until your arms and shoulders ache, or for many, climbing several, or sometimes even one, flights of stairs?
Once you see the difference between aerobic and anaerobic, this knowledge can help you build better health and fitness. So let’s start with a bit of history.
Dutch scientist Anton van Leeuwenhoek was the first to describe the microscopic components of muscle fibers in the middle of the seventeenth century. (He also was the first to observe and describe bacteria.) By the early 1800s, it was clear that two different types of human muscle fibers existed. Through the microscope, one showed a red color, and the other white. In humans, muscles are made different than in other animals such as birds. In chickens, for example, whole muscles are either red or white. The red muscles—the “meat”—are found in legs and thighs, while the white make up the breast. In humans, however, most muscles contain both red and white fibers (the exceptions are jaw muscles, which are predominantly anaerobic).
In 1863, French scientist Louis Pasteur coined the words aerobic and anaerobic. He was studying bacteria—and those that live only in the presence of oxygen he called aérobie. Aerobic comes from the Greek word “aero,” meaning air and “bios” refers to life. Some bacteria could not live with oxygen or air, and Pasteur called these anaérobie—anaerobic.
Around the same time in human physiology, the terms aerobic and anaerobic were used in relation to how the body obtained energy. They referred to two different complex energy transfer processes in cells—one that required oxygen (aerobic) and one that did not (anaerobic). More importantly, the source of energy produced in each muscle fiber was different. The red, aerobic fiber used fat as its source of energy. In order to convert fat to energy, this required oxygen—a reason for the large amount of blood vessels in the human body and in these muscle fibers—and for the cell components that aided this process which are called mitochondria. These iron-containing enzymes have a reddish protein called myoglobin.
In the white anaerobic fibers, none of these structures are needed. Energy is quickly generated through a process that uses sugar (glucose) as fuel that does not need oxygen.
As a result of further scientific research, these red and white muscle fibers in humans were also called type I, and type II, respectively. The red, type I aerobic fibers contract relatively slowly, and these would be called slow twitch. Their slow contraction would enable them to function for long periods—hours and days—without fatigue. This also allows them to support the body’s structures, especially the joints, bones, and arches of the feet.
The white, type II anaerobic fibers contract two to three times faster, and these were called fast twitch. They provide speed and power. But these attributes come with a price—they fatigue very quickly as their energy lasts only a very short time—a few seconds to about a minute (coincidentally, about as long as you can hold your breath).
In time, it was discovered that there was more than one type II muscle fiber, and these would be considered subdivisions of type II. Some of these fibers are pure fast twitch while others have a combination of both fiber qualities. Today, there are seven different fiber types, and as microscopic techniques improve, more may be discovered. But there are still two main types in humans—aerobic and anaerobic.
The list below is an overview of the function of each muscle fiber.
Aerobic Muscle Fibers
- Red iron-containing cells, and packed with blood vessels
- Slow-twitch sustains long-term activity
- Resistant to fatigue
- Uses (burns) fat for long -term energy
- Supports the joints, bones, and overall posture and gait
Anaerobic Muscle Fibers
- White cells with limited supply of blood vessels
- Fast-twitch for short-term power and speed
- Easily fatigued
- Burns sugar for short-term energy
Exercise physiologists in particular refer to the aerobic system when discussing the red, slow twitch fatigue-resistant fat burning muscle fibers, and the anaerobic system referring to the white, fast twitch power and speed, sugar burning fibers.
So which system—aerobic or anaerobic—is working in you right now as you’re reading these words? The surprising answer is both. It’s easy to see that aerobic activity is important all the time—to maintain various functions such as posture and movement, long-term, consistent energy, and circulation. But even though we’re not sprinting or lifting heavy objects, the anaerobic system is always performing some basic tasks such as burning sugar. In fact, within the complex metabolic pathways of energy production, burning some sugar helps maintain fat burning. In addition, the anaerobic system is always prepared to take action if necessary—humans have a “fight or flight” mechanism waiting to act should the need arise.
The real question is which system is predominating—which are you relying on? Is your body burning mostly sugar and less fat? If this is so, your anaerobic system is the one turned on more than your aerobic body. While you may not notice this, especially if it’s an ongoing problem, but your energy and endurance is not what it should be, you are vulnerable to aches and pains, body fat content is too high, and you’re under too much stress as the anaerobic system is connected with our fight or flight stress mechanism. In short, your health is compromised.
Instead, you want long-term energy to be free of fatigue, maximum support for your joints and bones, injury-free muscles, good circulation, and increased fat burning to slim down. You want both optimal health and great fitness.
Aerobic vs. anaerobic exercises
Certain types of exercise will provide benefits that will build the aerobic system long term. I refer to these simply as aerobic workouts, meaning they will provide the stimulus to improve fat burning for more energy, continuous physical support, improved blood flow throughout the brain and body, and reductions in body fat. Easy activities, such as walking, running, biking, swimming, and the many types of aerobics classes can accomplish this if the intensity of these workouts is not too high. Your heart rate is an accurate indicator—lower heart rate exercise is aerobic while performing the same workout with a higher heart rate would be anaerobic.
This is where the issues get more complicated. In the short term, any activity can help build the aerobic system, even very hard efforts. But continue these kinds of exercise routines for too long and your body will break down from injury, fatigue and ill health. You’ll become a casualty of the fit but unhealthy crowd.
The one important feature that differentiates aerobic exercises from anaerobic type—in addition to lower versus higher heart rate—is time. Just because a workout stimulates the aerobic system to burn more fat doesn’t necessarily means you should keep doing it. If maintaining such a workout regularly for, let’s say two or three months, it could suddenly turn on you, reducing aerobic function, lowering fat burning, suppressing the immune system, and causing physical stress with a reduction in aerobic muscle function. Whether it takes two months, two weeks, six months or a longer time frame, this type of workout program would be an anaerobic one. Anaerobic workouts performed for weeks can temporarily build the aerobic system, but at a cost.
For a workout to be truly aerobic, you should be able to exercise the same way for many weeks and months with continued benefits. And, when you’re finished each workout, you should feel great—not tired or sore, and certainly not ready to collapse on your couch. Nor should you have cravings for sugar or other carbohydrates—your workout should program your body to burn more fat, not sugar. Burning too much sugar during a workout means it’s anaerobic, using up stored sugar (glycogen). It can even lower blood sugar. The result is that you crave sweets.
This is a key to differentiating an aerobic exercise program from an anaerobic one. While even a hard weight-lifting session can produce some of these benefits short term, it does not in the long term.
Eventually, even moderately anaerobic workouts soon can reduce fat burning and even lower the number of aerobic fibers your muscles contain. Scientists have demonstrated this fact. They have measured this decline. It’s not something based on anecdotal evidence. I have measured it too, in couch potatoes, aerobic dancers, walkers, and professional athletes.
In a laboratory or clinical setting, the process of fat burning can easily be measured with a gas analyzer – a device that assesses the air you breath. By comparing the amount of oxygen you consume from the air, and the carbon dioxide your body expires, one can determine quite accurately the amount of fat and sugar you burn. As exercise improves fat burning long term, it reflects improvements in the aerobic system. Not so with anaerobic exercise.
For most individuals, the best way to determine whether an exercise is truly building your aerobic system is to check your heart rate – following the 180-formula.
For more information on aerobic and anaerobic workouts, the relationship to food intake, and other factors, including stress, see The Big Book of Endurance Training and Racing.