There are two priorities for those of us who dedicate a significant amount of our lives to the gym. The first is how to increase the amount of muscle we can make our bodies grow and the second is finding the best way to lose the body fat (BF) that hides it.
The difficulty that many have experienced is how to reduce their BF levels while preserving the lean muscle tissue they have laboured for so long to obtain. At one end of the spectrum are those that must dedicate themselves to achieving less than 10% body fat in order to enter competitions judged on visible muscularity. From bodybuilding to figure competitions, to modeling searches, there is a large population that is endeavoring to achieve just this goal. The opposing end of the spectrum is the larger proportion of the fitness population, who are those that simply want to drop body fat to see the six-pack, feel good, and earn some bragging rights. Those who must drop to very low fat levels have learned the best techniques and practices on how to do this and we can incorporate their practices into our own programs.
Many believe that the best way to decrease BF levels to competition level is to exercise at low intensity for 45-60 minutes once or twice a day pre-competition. Traditionally this approach began when we developed the knowledge of how the body uses energy to fuel long duration activity (we call it cardio). However, while the knowledge is sound, the resulting ideas of reducing BF are not as effective as it is believed.
The question is: what is the best way to preserve lean tissue, while stripping body fat? This is where the shades of grey have long been confusing the correct answer. The traditional approach for competitive figure and bodybuilding athletes is to increase cardio duration as early as 12 weeks pre-competition. The belief is that maintaining low intensity cardio activity at around 60% of max heart rate for 1 hour 6-10 times weekly is the best way to burn body fat, while preserving muscle tissue.
Is this, however, the best approach to cutting BF levels? First we need to understand the basic physiological processes that occur during exercise. Let us quickly review for anyone that is not familiar with these. For those of you who are familiar with physiology, this discussion is based on cardiovascular exercise in relation to BF reduction, as such; we will skip discussions of the creatine/phosphate system, as it is not relevant to our purpose.
The first and preferred energy source for your body during prolonged exercise is glycogen. This is simply sugar that your body converts carbohydrate into in order to fuel most processes in the body. You get glycogen from three places, stored in the liver, stored in muscle tissue, or from ingested carbohydrate.
Your next energy source to sustain activity is body fat. At a very useful 9 calories per gram, your BF stores represent the most efficient energy storage system you have. Your body knows that and works to ensure that a reserve supply is always present (12-18% for men and 18-22% for women is healthy). So this source of fuel is used once you have fully utilized the other energy systems.
The intensity of exercise is also a primary determinant for where the body uses energy. At lower exercise intensities (50-65% of max heart rate) the body’s energy use can be as much as 55-65% straight from BF storage, with the rest coming from glycogen storage, or if that is not available, catabolic muscle tissue breakdown. When exercise intensities increase to 75% to 90% of max heart rate, the fat utilization decreases and glycogen usage increases, with BF use dropping as low as 35-45% of overall energy expenditure.
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Knowing that once muscle glycogen stores have been exhausted the body will catabolize (break down) muscle tissue to make more glycogen, a high intensity long duration exercise session seems like a poor choice for reducing BF levels. Most people will exhaust glycogen levels within 20 to 30 minutes working at a higher intensity. This means that after that time they begin to sacrifice hard earned muscle in order to complete the activity.
At lower exercise intensities the body is more likely to increase BF utilization, and hence, not go to muscle catabolism for meeting energy needs. This in effect means that at 65% of max heart rate your body uses significantly more BF for energy then stored glycogen and is less likely to begin eating muscle.
Armed with this knowledge the world of bodybuilding and fitness figure modeling has adopted a less than efficient system of obtaining very low BF levels. If long duration and low intensity workouts are not the best way to decrease BF, then what is? Especially if high intensity exercise leads to muscle breakdown!