Obesity rates in North America have risen significantly across recent years. In 2002, the Canadian Fitness and Lifestyle Research Institute (CFLRI) determined a 55% national obesity average for young adults aged 20 years and up. Canadian health professionals continually strive to battle this epidemic, in hopes of fostering a preventative approach to disease and obesity. This article will provide answers to some of the more common inquires posed by overweight individuals; how does exercise reduce body fat, and what form of training is best for me?

In order to successfully answer these questions, a brief explanation of the metabolic systems associated with exercise and physical activity is required. By understanding the methods in which the body harnesses energy, one is able to cater their workout in order to improve their performance, appearance, or both.

ATP-PC System:
 The ATP-PC (Adenosine Triphospate-Phosphocreatine) system is the initial method of energy production in the body. This system (like all systems to be mentioned) provides our muscles with ATP; a molecule needed in order to generate a skeletal muscle contraction. The ATP-PC system is typically associated with anaerobic exercises such as resistance training, sprinting, power lifting - actions which require a higher level of perceived effort, in a short period of time. This system is responsible for the ATP produced within the first 30 seconds of exercise. Individuals ingesting creatine supplements attempt to increase the recovery rate of this energy system.

Anaerobic Glycolysis:
 The energy harnessed following the ATP-PC system stems from Glycolysis, or, the breakdown of sugar. When ingested, carbohydrates are broken down and transported to various locations in the body, including our muscles. As a result, muscle cells contain a finite concentration of stored glucose. The breakdown of glucose aids in muscle contraction by generating ATP. This catabolic process is said to occur in our skeletal muscle cells after the ATP-PC system has been exhausted. Anaerobic glycolysis is the dominate method of energy transfer between 30 and 90 seconds of an exercise bout. Activities requiring short bursts of high intensity effort would utilize both the ATP-PC, and anaerobic glycolysis methods of energy transfer.

Oxidative Phosphorylation:
 This aerobic method of energy production makes use of oxygen, among other substrates, to form ATP. It yields the greatest amount of Adenosine Triphosphate with respect to the systems above, and is the method of energy transfer associated with lipid oxidation - fat loss. This system is the dominant form of energy production after 2 minutes of exercise, and remains so until cessation of physical activity. Oxidative phosphorylation occurs within our cells via an organelle known as the mitochondria. This system is associated with endurance type activities; marathons, biking, hiking, and so forth.

To summarize, there are three energy systems which predominate prior to performing a bout of physical activity. The energy system associated with lipid oxidation (fat burning) is oxidative phosphorylation. This process takes place in the mitochondria of our cells. It is the dominant form of energy production after approximately 2 minutes of exercise.

In order to maximize lipid oxidation, an individual should:

  • Perform low-moderate* intensity exercises for a minimum of 20 minutes a session
  • Resistance train most, if not all areas of the body
  • Ingest the greatest proportion of your allotted carbohydrate intake for the day, prior to performing an exercise routine

*I will address the notions behind the intensity of the routine in the explanatory paragraph below

These are the 'secrets' to fat loss most organizations attempt to conceal from the public, as silly as it seems. Keep in mind this article is not meant to address nutrition; it is solely covering the training adaptations associated with fat loss.

For those interested as to why these reasons work, so that you may personalize or modify a given routine, please read on. Those who have attained the information they were seeking may disregard what is to come.

The breakdown of each reason and why it works:
Perform low-moderate intensity exercises for a minimum of 20 minutes a session

Most 'health professionals' encourage the idea of low to moderate intensity exercise for three reasons:
1. It is a safe way to initiate an exercise regimen without risk of injury or heart attack.

2. It entices overweight individuals to engage in physical activity. Members of the sedentary population would much rather prefer 'moderate' intensity exercise as opposed to 'vigorous' or 'high intensity'. By propagating the notion that exercise doesn't always have to be 'all-or-nothing', participation levels are likely to increase.

3. As mentioned above, the energy systems associated with a higher level of perceived effort are the ATP-PC and Anaerobic Glycolysis systems. These systems rely on substrates like glucose and creatine for the provision of ATP to produce a contraction. As an exercise bout lengthens in duration, the concentration of glucose within skeletal muscle cells depletes. The order in which the body utilizes fuel for activity is dependent on a variety of factors, one of them being dispensability. Glucose, being the most 'dispensable', is consumed first; lipids (fat) next. Glucose molecules are easily broken down, and release approximately 4 calories of energy for every gram. Fat releases 9 calories of energy per gram; more than twice that of a single glucose molecule. How is this significant? The longer one engages in a bout of physical activity, the greater the energy demands of the body. Fat provides a significant amount of energy to working muscles in comparison to glucose, and as a result, is the ideal compound for prolonged periods of exercise. A moderate intensity exercise session promotes lipid oxidation, as it does not require major contribution from other energy systems, except for when initiating the exercise. The minimum recommendation of 20 minutes is derived from calculating the Respiratory Quotient for a given individual and will not be discussed in this article. The longer one performs an aerobic bout of exercise, the greater the degree of lipid oxidation.

Resistance train most, if not all areas of the body:

As mentioned above, oxidative phosphorylation occurs within the mitochondria of our cells. Studies have shown that individuals who strength train, in conjunction with aerobic training, yield the best results when considering fat loss. Some suggest the increased amount of calories burnt when combining the two is the cause for this heightened response. Others believe that an increased mitochondrial density (a higher proportion of mitochondria per muscle cell) which accompanies training is responsible for the accelerated metabolism seen in athletic individuals; the more one trains, the more efficient the individual's metabolism, the greater the proportion of fat consumed. Both theories in my mind are plausible, but to say one is more correct than the other would be erroneous. I'll leave this one up to you.

Ingest the greatest proportion of your allotted carbohydrate intake for the day prior to performing an exercise routine:

While this isn't an article addressing nutrition, the notion of proper nutrient intake cannot be undermined. An adequate amount of carbohydrates should be ingested prior to, and after a workout. The specifics of nutrition will be addressed in a future article.

Patience and perseverance