If you do an internet search on “weight loss,” you’ll find many sites proclaiming that aerobic exercise is the best type of activity to lose weight. They usually suggest doing your workout first thing in the morning or hours after you’ve eaten so that your body will burn fat instead of carbohydrates.
Unfortunately that approach doesn’t work for every person’s schedule. It also doesn’t do anything to prevent the new fat deposits that form precisely because of eating carbs. However, an examination of biochemistry shows why anaerobic exercise can be more effective than cardio, regardless of the timing of your work out.
Cellular Respiration
Cellular respiration refers to the metabolic reactions that take place in cells in your body to make use of chemical energy from food. Cells cannot directly use the energy stored in carbohydrates, fats or proteins. They must first be broken down into a more usable form known as adenosine triphosphate (ATP).
Glucose metabolism begins with a process called glycolysis. It occurs in the cytoplasm of the cell and does not require the presence of oxygen. During glycolysis, a single molecule of glucose is converted into 2 molecules of pyruvate, an important biochemical compound. The net output during glycolysis of one molecule of glucose is 2 molecules of ATP.
If oxygen is present, pyruvate is converted to acetyl-CoA which then enters the Krebs cycle. This multi-step process, also known as the Citric acid cycle, results in the production of 36 additional molecules of ATP. The net output of aerobic respiration is 38 molecules of ATP for every molecule of glucose used.
During anaerobic respiration (respiration in the absence of oxygen), glucose is broken down to form only 2 molecules of ATP. Since oxygen is not available for the conversion of pyruvate to acetyl-CoA, lactic acid is formed instead. Therefore, under anaerobic conditions, glycolysis is the only source of ATP and only 2 molecules of ATP are produced for every molecule of glucose used up.
Aerobic and Anaerobic Exercise
During aerobic exercise, oxygen is a reactant in metabolic reactions. Many types of activities are aerobic; the common factor is a moderate level of exertion for an extended period of time. Examples include: jogging, cycling, swimming and cross-country skiing. Anaerobic exercise is high-intensity activity done over a relatively short period of time. Weight training, sprinting and resistance training are anaerobic activities.
Because of the availability of oxygen, energy use during aerobic activity is efficient with 38 molecules of ATP being produced from every molecule of glucose. In contrast, anaerobic work is inefficient, producing only 2 molecules of ATP for every molecule of glucose. Thus, to generate the same amount of usable energy (ATP), anaerobic exercise consumes 19 times the amount of glucose that aerobic exercise does.
Carbohydrates are broken down during digestion to glucose. Increasing blood glucose levels stimulates insulin to be released from the pancreas. The role of insulin, among other things, is to convert excess glucose to triglyceride and store it in adipose tissue. Anaerobic activity results in the rapid consumption of glucose in the bloodstream, making it unavailable for conversion to fat by insulin. In this way, anaerobic exercise prevents the storage of fat.
If the concentration of glucose in the bloodstream falls below desirable levels, triglycerides stored in fat cells are converted by glucagon into free fatty acids (FFA). FFA are broken down in cell mitochondria to produce acetyl-CoA which then enters the Krebs cycle to produce ATP. By keeping blood glucose at sub-optimal levels, anaerobic exercise can be an effective way to burn stored fat.
Disclaimer: This information is for educational purposes only and should not be considered as medical advice. It does not replace the advice of the physician who cares for you. All medical advice and information is incomplete without a physical exam, which is not possible without a visit to your doctor.
Adrienne Larocque - Dr. Larocque is an award-winning scientist who has published more than 20 articles in peer-reviewed scientific journals.
