Anaerobic Workouts: What is Anaerobic Exercise
Anaerobic exercise causes our muscles to consume fuel in ways that don’t require the presence of oxygen. An anaerobic workout (which literally means “without oxygen”) relies on a unique set of metabolic processes briefly described below. These processes take place when our bodies are moving at a level of intensity that pushes our heart rate above 80 percent of its maximum speed (PHR).
Anaerobic exercise can benefit our overall health and can provide excellent support to a well-balanced fitness regimen. But as you add an anaerobic component to your routine, it may help to know more about what these anaerobic pathways do for our bodies and why we have them in the first place. A better understanding of anaerobic muscle activity can help you build strength during short bursts of intense activity, which can have a powerful effect on athletic training.
What is Anaerobic Exercise
As we begin exercising and steadily increase our activity levels, our heart rate speeds up in order to keep pace with our body’s growing demand for oxygen and fuel. In order to function, muscle cells require both oxygen (supplied by the lungs) and energy, which is initially supplied by glycogen stored in our muscle tissue. As muscle glycogen is depleted, the body turns to glucose supplied by the liver and fat taken from storage and metabolized in the presence of oxygen.
During aerobic activity, in which the heart rate stays below 80 percent of our PHR, our muscles rely on oxygen and these three sources of fuel: glycogen, glucose and fat. All three are used up over time. But as it happens, we’re designed with a life-saving mechanism that retains a very limited supply of glycogen and specialized phosphates in reserve within our muscle tissue. When we need a sudden burst of speed, aerobic pathways are bypassed and our muscles tap these reserves using a non-oxygen-dependent, or anaerobic, process.
When we push our heart rate above 80 percent, these anaerobic pathways activate. As this happens, we become capable of a powerful burst of strength that can last for only a few seconds or about two minutes at the most. During that time, the lactic acid by-products of muscle metabolism, which are usually cleared away by the bloodstream, become backed up. This causes a burning sensation in our limbs which coincides with almost immediate exhaustion and complete muscle failure.
A Few Examples of Anaerobic Exercise
Anaerobic exercise pathways can help us call on a ready (if small) supply of energy for explosive actions. Very few of us can keep our heart rates above 80 percent of our maximum for more than a minute or two at time. But while we exist in this zone, our muscles, hearts, and other systems are being taxed and then forced to recover in ways that can greatly increase our strength and conditioning over the long term.
Anaerobic exercises include sprints (but not long runs), swim sprints (but not sustained laps), power lifting, and burn-down resistance training or lifting to the point of failure. These anaerobic exercises are embraced by athletes who rely on short bursts of controlled speed and power on the sports field. Many track and field teams rely on training routines with an anaerobic component. Body builders tend to use anaerobic moves as well, even though their goals are usually focused on mass rather than strength. While shifting our metabolic pathways, anaerobic exercises also tend to over-tax our muscle fibers. This leads to the miniscule damage, called hypertrophy, that makes muscles grow bigger.
How can you tell if an activity can be categorized as aerobic or anaerobic? The line between these two metabolic pathways is not always clear, through heart rate can be a reliable indicator. If your heart rate falls below 80 percent of your maximum, chances are you’re burning glycogen, glucose and fat and you’re doing it using oxygen (i.e., you’re still in the aerobic zone). This is true no matter how tired your body becomes.
But if your heart rate rises above 80 percent and you feel the burning sensation of lactic acid building up in your muscles, you’ve probably crossed the threshold into anaerobic exercise. You won’t be able to stay in this phase for long. But a good anaerobic workout will provide you with just enough rest time to recover your muscle function before sending you back across the line again.
The Benefits of Anaerobic Exercise
Anaerobic exercise can build muscle strength, which is one of the primary reasons it’s embraced by athletic trainers everywhere. Regular anaerobic training can make a quick burst of speed much quicker and a short burst of force much more powerful.
Regular anaerobic training also improves and conditions the specialized muscle fibers (often called fast-twitch muscles) that are called upon when the body needs those small reserves of phosphates and glycogen. When the anaerobic pathway springs into action, well-developed fast-twitch muscles are quicker to respond and better able to recover afterwards.
Anaerobic exercise, especially resistance training and high impact activities like jumping rope, can build bone strength. This can ward off the effects of osteoporosis and generally make our bones more resistant to fracture.
Can a Healthy Workout Routine Involve only Anaerobic Exercise
A balanced, healthy path to fitness should include a blend of both aerobic and anaerobic exercise. Too much aerobic exercise with no anaerobic component can neglect the strength of the upper body and prevent the development of fast-twitch muscles and anaerobic fuel reserves.
Too much focus on anaerobic exercise is more difficult than the reverse, since it isn’t easy to move back and forth between resting and anaerobic heart rate zones. But it’s also unwise. For example, lifting alone with no regard for overall aerobic conditioning or cardiovascular strength can place strain on the heart, and can also stand in the way of your lifting goals, whatever they may be.
Depending on your athletic performance requirements, a professional trainer or coach can help you balance aerobic and anaerobic exercises to make the most of both. Consider adding interval training to your routine, a workout strategy that moves the body back and forth across the aerobic-anaerobic threshold. See our article on Interval Training for more detail.