Many people have difficulty determining the difference between aerobic and anaerobic exercise, but the difference is simply the amount of oxygen received by your muscles. Your body does not receive the same amount of oxygen during an intensive exercise period as it does during a lighter period of exercise, making it impossible to maintain a high-intensity workout for too long. The current trend in conditioning is higher intensity training protocols for cardiovascular conditioning and weight management (anaerobic) versus the traditional focus on steady state low-moderate intensity training protocols (aerobic).
To make sense of this trend you need to understand how the body responds to high intensity anaerobic interval training from a cardiovascular standpoint. There are two types of metabolic/energetic pathways used for generation of energy in all our cells: aerobic and anaerobic. Aerobic means with oxygen and requires the presence of oxygen in the cell producing energy. Anaerobic means without oxygen when you have worked so hard that your demand for oxygen overcomes your supply, and cells produce energy without the presence of oxygen, but rather on the calories that you have stored in your body through eating. A single cell can either produce energy aerobically or anaerobically at any given time, but never both at the same time.
When a muscle has sufficient oxygen present it will burn glucose aerobically. This provides much more energy than burning glucose anaerobically which happens when the cell does not have enough oxygen.
Muscles can also generate energy from fat aerobically. Fat provides much higher amounts of energy than glucose, but burning fat requires even more oxygen availability relative to the amount of energy needed per unit of time.
When a muscle cell needs to produce a lot of energy in a hurry, it is forced to use anaerobic energy pathways, including burning glucose. This results in the by-product of lactic acid. When it is forced to burn glucose anaerobically, muscle will rapidly use large amounts of glucose. So the higher the intensity of exercise, the more the muscle cells will be forced to use anaerobic metabolism to burn glucose, rather than burning glucose aerobically or using fat for a fuel. This rapid depletion of glucose, along with the buildup of lactic acid, then limits how long a muscle cell can keep generating energy anaerobically.
Intensity is different for different people depending on their fitness levels. For example, walking on flat ground at 3 MPH is low intensity exercise for fit runners. Their muscles can generate most of the energy required aerobically because they have sufficient oxygen delivery capacity to the working muscles relative to the amount of energy required per unit of time. However, for a severely de-conditioned person walking at the same pace, this is an anaerobic exercise because there is not sufficient oxygen delivered to generate the required energy aerobically. Thus, the muscles are forced to go anaerobic.
Exercises requiring short intense efforts that cannot be maintained for long periods (less than 2 mins.) are classified as anaerobic and exercises that are less intense and can be maintained for long periods of time (over 2 mins.) are classified as aerobic. The best conditioning response will occur if the work interval time, work/rest ratio, and work interval intensity of the conditioning program are matched to the specific energy requirements.
For example, if a football lineman wanted to train for his specific position, he would take into account the fact that the average play lasts from 4-20 seconds with a recovery period of 10-60 seconds. He would want to focus on doing high intensity intervals where he reaches a high level of fatigue in 20 seconds so that he has stressed and caused adaptation of the specific anaerobic energy pathways required for the position. He would then match the recovery to that of this position or make it shorter to increase the challenge as he adapts to the exercise stimulus. For a soccer half-back athlete, he/she would need to use much longer intervals as well as a corresponding lower intensity to condition the athlete for the longer duration efforts required by this sport.
Stay tuned to next month’s NewsShaper for the continuation of Anaerobic and Aerobic Conditioning. We will discuss HIIT and Cardiovascular Conditioning, as well as the hormonal effects of High Intensity Short Duration Interval Training versus Steady State Cardiovascular Training.