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7.19.2011

Aerobic vs. Anaerobic Exercise

Strictly speaking, the terms "aerobic" and "anaerobic" refer to the presence and absence of oxygen, respectively.  Most of our cells prefer to get their energy by using oxygen to fuel metabolism.  During exercise with adequate fuel and oxygen (i.e., aerobic), muscle cells can contract repeatedly without fatigue.  This type of workout will be fueled mostly by fat cells stored throughout your body.  During anaerobic or non-oxygen conditions (i.e., higher intensity exercise), muscle cells must rely on other reactions that do not require oxygen to fuel muscle contraction.  Anaerobic activity relies mostly on carbs stored in your muscles as glycogen.  The burning of glycogen in the muscles produces waste molecules that can impair muscle contractions.  In other words, you fatigue!
Depending on your fitness goals will determine where most of your activity should occur.  For the vast majority, overall health and weight loss are the main goals.  For this group, about 80% of your activities should remain in the aerobic state.  These lower intensities will allow your body to burn a higher percentage of your calories from fat, resulting in a slow and steady weight loss (as long as your diet is right).  Aerobic exercise tends to be less stressful to muscles, joints, and your heart, which may be important for individuals with arthritis, heart disease, or high blood pressure.  For athletes, or those with more competitive goals, a typical week should see 40-60% of your workouts in an anaerobic state.  These workouts will teach your body to store more sugar in your muscles which will result in more rapidly improving your exercise capacities, tolerance, and performance.
When starting a training program, most trainers like to have their clients/athletes start with lower intensity exercise (i.e., aerobic exercise).  However, a high reliance on anaerobic metabolism is unavoidable for some types of exercise or activities.  For instance, lifting weights is anaerobic.  That is why muscles fatigue so rapidly with this type of training.  Other types of activities, such as walking up stairs, can also be anaerobic - especially if you are unfit or climb too fast.
Fortunately, you do not need sophisticated equipment to detect when you transition from aerobic to anaerobic exercise.  As we approach and pass our anaerobic threshold intensity, we start to breathe harder and exercise simply becomes uncomfortable.  Typically, you can’t finish a sentence without having to take a breath.  However, if you simply love gadgets, you can use a heart rate monitor to record the heart rate at which you sense these symptoms of developing over-exertion.  You then know that heart rates below this value occur when you're in your aerobic zone, and heart rates above this value reflect an increasing anaerobic contribution to your workout.
Steven Harben
Recreation Programmer
City of Wylie