Anaerobic and Aerobic Metabolism and Exercise

There are two types of metabolic systems used within the body to create energy for muscle contractions: anaerobic metabolism and aerobic metabolism. These metabolic systems are used to identify types of conditioning exercises, basing the classification of the exercise on the metabolic pathway supplying the majority amount of energy.

The most important difference between these two systems is the need for and use of oxygen to create energy. Anaerobic metabolism creates and uses energy without oxygen while aerobic metabolism, which converts glucose and fats into energy, must use oxygen.

Contrary to common perception, anaerobic and aerobic metabolic systems often function simultaneously. In fact, all physical activity starts with anaerobic metabolism. Since anaerobic metabolism does not require outside (of the muscle) materials (like oxygen), it can be performed within the muscle’s cells rather quickly, making this system the body’s “go-to” energy source when exercise starts. With essentially no delay from the time the body needs energy to the time anaerobic metabolism produces this energy, anaerobic metabolism provides the body with energy while aerobic metabolism (which takes longer to produce energy) ramps up.

Anaerobic metabolism can create energy quickly enough to be sufficient for sudden bursts of intense activity over a short period of time (jumping, sprints, other explosive movements). However, if physical activity lasts for longer than a few seconds, the anaerobic metabolic pathway cannot keep up with the body’s energy demands. At this point, the percentage of total energy being produced for activity through aerobic metabolism increases. Aerobic metabolism accounts for an increasing amount of energy the longer the exercise session lasts.

Exercise

As previously mentioned, both anaerobic metabolism and aerobic metabolism are used during most physical activities. The degree to which each metabolic system contributes to the total energy available is determined by the intensity and duration of the exercise. So, how do you know if you’re doing aerobic conditioning or anaerobic conditioning? Generally speaking, the “rule” used by exercise physiologists and fitness professionals is this:

If the intensity of the exercise/activity is low enough that the body has enough oxygen to create the energy needed, the exercise/activity is aerobic.
If the exercise/activity is of high enough intensity or does not last long enough for the body to process oxygen to produce enough energy, the exercise/activity is anaerobic.

Anaerobic activities cause the body to experience what’s known as an “oxygen debt”. This is why you continue to breathe hard after you’ve stopped exercising.

Anaerobic Exercise

Anaerobic exercise elevates the heart rate for a brief period and then allows the heart rate to drop (but it will still be elevated compared to the resting heart rate) during rest periods. Rest is very important during anaerobic exercise in order to allow the body enough time to recover from the oxygen debt incurred during the previous bout and to ensure that the body has replenished an adequate store of energy.

Type of exercise activity: explosive, short-duration, burst activities
Intensity level: high
% of maximal effort: 90% - 100%
Number of times per week (when out of season): 3-4
Duration of each bout: 10 seconds – 2 minutes
Work-to-rest ratio: 1:2 – 1:5 (i.e. if you sprint for 10 seconds, you need to rest 20-50 seconds between each bout). The shorter the rest period between bouts, the more intense the overall activity will be. However, shorter rest periods will also lead to a faster decline in performance during the exercise.
Examples: 60m sprints, 100m sprints, jump exercises (like those found in lower body plyometric training)

Aerobic Exercise

Aerobic activities elevate the heart rate and maintain this elevated heart rate for an extended time. These activities often involve repetitive, whole-body, large-muscle movements. As compared with anaerobic exercise, aerobic exercise is easy to regulate by simply speeding up or slowing down the pace of the activity.

Type of exercise activity: continuous, long-duration, sustained activities
Intensity level: moderate
% of maximal effort: 60% - 90%
Number of times per week (when out of season): 3-6
Duration: 20-60 minutes
Examples: running, cycling, swimming, using the elliptical, using the rowing machine

Interval Exercise

Interval training allows you to exercise at a higher intensity over a longer period of time than continuous aerobic training. Exercising in an interval-based activity allows for a more varied exercise routine, including playing recreational sports (rather than running around a track or on a treadmill for the entirety of the workout).

Type of exercise activity: intermittent burst activities mixed into a continuous activity (in other words, this combines an anaerobic exercise with aerobic exercise)
Intensity level: alternating relatively intense activities with lower intensity activities
% of maximal effort: burst activities: 80% - 100%; continuous, lower intensity activities: 30% - 60%
Number of times per week (when out of season): 2-3
Examples: running mixed with brief sprints, basketball, racquetball, 2- or 3- person volleyball, swimming mixed with brief sprints