Aerobic Exercise


Aerobic and Anaerobic Workouts: What is Aerobic Exercise

Aerobic exercise describes any continuous activity of moderate intensity that goes on for a sustained period of time. While we workout at this level, our pulse stays elevated above 60 but below about 80 percent of our peak heart rate (PHR).

Why do we call this aerobic exercise, and how is this this activity distinguished from anaerobic exercise? Most important, what do these terms mean for our workout plans and athletic performance? Below, we’ll cover some of the basics of aerobic exercise physiology and discuss the benefits of working out at this level. For additional information on the subject, visit our related articles on Anaerobic Exercise and Heart Rate.


What is Aerobic Exercise, and How Does it Affect Our Workout Goals

When we’re engaged in low intensity activity or just beginning to warm up, our heart rate stays just above resting levels and our muscles can handle the strain we place on them for prolonged periods of time. At this activity level, muscle tissues consume oxygen delivered via the bloodstream from the lungs (“aerobic” means oxygen-dependent), and for fuel, they rely on a substance called glycogen, which is stored in the muscles for easy access. This glycogen is broken down into glucose in order to be used by our muscle cells.

As the duration of aerobic exercise increases, the stored glycogen in our muscles is gradually used up, and our liver begins to supply glucose to our muscles directly. The liver also begins to elevate fat metabolism. At this point, our muscle cells are obtaining fuel from three sources: fat, glucose, and any glycogen stores we still have in our muscles. To convert any of these three into energy, our cells require a steady flow of oxygen.

We may be in the middle of a light, one-hour jog while this is happening. Aerobic activity is taking place in our muscles, oxygen is flowing, and our cells are deriving fuel (via an aerobic process) from a combination of fat, glycogen and glucose. A by-product of muscle activity called lactate or lactic acid is building up in our muscle fibers, but this is happening so slowly that our bloodstream can easily clear it away.

A Quick Shift to Anaerobic Exercise

In the middle of this pleasant jog, say a fierce dog suddenly jumps over a fence and chases us. To save ourselves, we run fast for the nearest tree. This requires a quick burst of very intense muscle activity that can’t be sustained for more than a few seconds. During this sprint, our muscles switch over to an anaerobic process that does not rely on oxygen. Certain muscle cells activate within our arms and legs called “fast-twitch” muscles, which burn anaerobically through a very limited supply of high energy phosphates and glucose, both of which are stored in our muscles for exactly this purpose.

This quick anaerobic burst may save our lives, but it also causes a back-up of lactic acid by-product that generates a burning sensation in our limbs. And it places a strain on the heart, which speeds up to maximum intensity (above 80% of our PHR) for just a moment.

After we’re safe, we resume our steady jog, our heart drops back below 80% of our PHR, and our muscles return to aerobic fuel burning processes. Once again, oxygen allows our cells to consume fuel from fat (more so as we stay below 70% PHR) and carbohydrates (more so as we stay between 70 and 80%).

How Can we Distinguish Aerobic from Anaerobic Exercise

While anaerobic exercise moves involve quick sprints and intense bursts of unsustainable activity, aerobic exercise involves sustained, oxygen dependent activities like jogging, marathon running, swimming, dancing, and singles tennis. If you aren’t sure an activity qualifies as aerobic, consider these signatures of aerobic exercise:

Aerobic activity can be sustained for several minutes or more without a rest.

Our muscles can keep engaging in aerobic activity despite mild to moderate burning. (Intense burning that forces us to stop moving means high lactate build-up, which suggests anaerobic muscle activity).

Aerobic activity keeps our heart rate above 60% but below 80% of our PHR.

The Benefits of Steady Aerobic Exercise

Making aerobic exercise a regular part of your workout routine can have several benefits, including the following:

  1. Aerobic exercise builds strength in the lungs and the muscles that control them. Over time, our lungs increase their capacity and our respiration and oxygen intake become more efficient.
  2. Aerobic exercise strengthens the heart muscle, which means we get more work out of each strong beat. Blood pressure drops, arteries become more flexible, and oxygen delivery improves.
  3. Aerobic exercise increases strength and conditioning in all of our muscles.
  4. Aerobic exercise burns body fat.
  5. Sustained aerobic exercise trains our bodies to store more carbohydrates and glycogen within our muscle tissue, which increases endurance.
  6. Aerobic exercise may help increase the number of red blood cells circulating in our bodies, which can improve oxygen delivery to our cells. This can cause a cascade of benefits in every area from mental health to disease resistance. 

Can a Fit Lifestyle Include only Aerobic Exercise

While aerobic exercise is a key component of endurance and cardiovascular health, aerobic activity alone might not provide a complete and balanced workout regimen, especially for athletes who depend on quick bursts of activity for peak performance.

Anaerobic exercises, for example sprints and strength training, can help develop the metabolic pathways that support fast twitch muscle activity. Adding anaerobic exercise to your routine can also help develop strength in the upper body, an area often neglected by popular aerobic exercises that tend to focus on the legs.

A combination of aerobic exercise and anaerobic exercises, usually called interval training, can support strength and conditioning through both pathways. A great interval training workout pushes the body back and forth between steady, endurance-focused, aerobic exercise moves and intense bursts of fast-twitch, anaerobic exercises. See our related articles on Heart Rate and Interval Training for more detail.

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