With all of the misinformation about cardiovascular training in the fitness industry today, clients are confused about the best way to train. Tag lines like, “The fat burning zone” “Interval training for fat burning” and “Two 10 minute workouts a day is all you need” have most people exhausted before they even begin their cardiovascular workout! Additionally, most people have no idea how hard or for how long they should be working out to achieve their training goals.
What is the Fat Burning Zone?
The “fat burning zone” is a phrase that has been hyped up and advertised as a selling tool by some equipment manufacturers as well as supplement companies directed at the consumer. People buy the idea because it suggests that working out at a lower intensity is better for burning fat. The truth is there is a degree of intensity at which a greater percentage of fat is being used as the primary source of energy during a workout. This is typically during a lower intensity workout. However, if the client’s goal is weight loss then what matters most is total caloric expenditure. Considering the fact that this information has been available for quite some time now, it surprises me how few people actually understand it.
It is simple math, at lower intensity levels, the ratio of fat burned to carbohydrate may be 50:50. If total caloric expenditure is 100 calories during your workout then you will have burned 50 fat calories. As the intensity increases, the ratio of fat to carbs may look more like 30 percent fat, 70 percent carbs. But if the total output of energy is 300 calories, you will break down 90 fat calories and 210 carbohydrate calories giving you a greater total expenditure of fat burned.
It is also important to note that no single energy system acts in isolation. Energy transfer during exercise is best thought of as a continuum with considerable overlap from one system to another. The relative contribution depends on duration and intensity as well as the available type of energy and the client’s fitness level. As the client’s fitness level increases, oxygen consumption is increased for energy production as well as the ability to shunt fat into the muscle to be burned as energy during higher intensity workouts.
Another consideration is the fact that fat oxidation during exercise is sensitive to the interval of time between eating carbohydrates and the onset and duration of exercise. Eating carbohydrates before beginning to exercise reduces the mobilization of the free fatty acids into the plasma, thereby reducing "fat burning" for energy. The body relies heavily on carbohydrates and less on fat when carbohydrates have been eaten during the previous few hours. While it may be preferable (in terms of burning fat) not to "carbo-load" shortly before a workout. I am not suggesting one should not eat carbohydrates before a workout, especially if your client has a history of hypoglycemia
Studies conducted from the University of Texas in a recent article of The Sports Science Exchange suggest that when working in the “fat burning zone,” increased fat burning may not go into effect for up to 100 minutes after the commencement of cardiovascular activity. This was demonstrated when working out 4 hours after only 140 grams of carbohydrates had been consumed. Conversely, and interesting to note, exercising a couple of hours after a meal will help oxidize fat, so that less fat will be stored. This is a strong case to encourage your clients not to exercise on an empty stomach in an effort to burn fat.
The point here is not to discourage exercise at lower intensity, it is simply to debunk the myth of the “fat burning zone.” Working out at lower intensities does serve our clients’ needs in many instances, for example, the client/ athlete who needs a day of active recovery. For many of my more “intense” clients just getting them to workout for a long duration at a lower intensity is a workout! Another example would be the sedentary client who is working his/her way up to greater oxygen consumption and incremental increases in aerobic capacity or peripheral adaptation. Clients recovering from illness or injury may also benefit from this type of workout as well as someone who needs to focus on increased joint stability.
Exercise is a powerful tool that we can use to control fat cell size and number. If burning fat is the goal, then efforts should be made to perform as much work possible in the time available.
Interval training is one of the most effective ways to burn a large number of calories while conditioning both the cardiovascular and muscular systems. Because muscle is the primary organ that oxidizes fat, it makes sense to increase the amount of muscle fibers through strength work. Additionally, since lean tissue is metabolically more active than fat, when the percentage of lean tissue increases, so does the resting metabolic rate. For example one pound of muscle will burn between 30 to 50 kcal per day conversely, one pound of fat will burn two kcal per day. If our clients gain 10 pounds of muscle, that can add up to 300 to 500 extra kcal expended per day at rest! An additional 500 expended calories per day will equate to one pound of fat loss per week. To some clients, one pound of fat does not seem like a huge motivator but when I tell them to imagine a three-pound can of Crisco, three pounds in three weeks becomes substantial! And with age causing atrophy of muscle and increased fat gain, it makes sense to reverse the effects of aging. Considering that an extra 10 pounds of fat will only burn a grand total of 20 kcal per day compared to three to 500 kcal if it were muscle, the benefits of fitness become obvious.
Interval training (short repeated bouts of intense exercise over a period of time) is a great way to shock the body, increase physical adaptation, power and speed. Besides the many physiological benefits, it will help your clients’ self-confidence. I have found that most people are stronger than they think they are and using interval training to push my clients (gradually) has proven successful to increase personal strength and self awareness. Interval training, whether done on the treadmill, in a cycling class, in a circuit training session or with weights,is a great use of time, energy and calories. (For ideas on interval training, refer to my article "Treadmill Interval Training" under "related content" at right).
I am in favor of interval training for the ultimate fat burning effects both during and after the workouts. In my experience, the benefits of interval training are seen fairly rapidly in cardiorespiratory response, adaptation and lean body mass. Interval training is also a great road map for my clients. It is easy to set performance benchmarks which give them a good idea where they are starting and a clear vision for where they need to go. Additionally, with interval training I can easily identify structural weakness and design a program that will be beneficial to my clients overall fitness needs/goals
An important point and something that I rarely see discussed in the fitness publications is the after-effects of increased metabolism due to exercise. According to the ACSM, total energy expenditure by muscles at rest can account for about 25 percent of total expenditure but exercise can increase this expenditure by as much as 50 times. And by exercising for 30 to 60 minutes at 70 percent VO2max, a woman can increase her expenditure by nine to 18 percent and burn an extra six to 12 grams of fat each day - at rest! Under the same conditions a male can increase daily additional expenditure by 13 to 26 percent and burn an additional 16 to 31 grams of fat at rest. Additionally we know that fat oxidation and carbohydrate utilization is enhanced for many hours following a workout. Therefore, when we eat after a workout, we will oxidize more fat from the meal thereby reducing the amount of fat stored.
In conclusion, with a true and accurate understanding of the benefits of long, low intensity workouts, versus short, intense interval-type training, both can be of benefit to our clients. And frankly, both should be incorporated into a varied workout program. We never do our clients a favor by offering the same routine each day of the week. Since no one energy system works in a vacuum, if the goal is weight loss, the focus needs to be a measure of increased energy expenditure and decreased caloric intake. Bottom line, eat less exercise more.
- Coyle, Edward F. Fat metabolism during exercise. Sports Science Exchange Vol. 8, 1998
- Mole, P.A. Daily exercise enhances fat utilization and maintains metabolic rate during severe energy restrictions in humans. Sports Medicine, Training and Rehabilitation 7:39-48, 1996
- Mole, P.A. Exercise and the fat balancing act. ACSM Health and Fitness Journal. May/June 1997
- Smith, Jessica. Revisiting energy systems. IDEA Health and Fitness Source. May 2002