Specificity principle and endurance performance for athletes
Bulletin No. 52, Endurance Performance Part II
Parrillo Performance Products
(800) 344-3404
To maximize fat burning during aerobic exercise you should do it first thing in the morning before breakfast or else right after weight training. During these times liver and muscle glycogen are relatively depleted and insulin levels are low. These conditions promote the use of body fat as a fuel source. Aerobic exercise should be performed at moderate intensity for 30 to 60 minutes per session, generally. A good way to gage intensity is that you should be breathing hard and sweating. For maximum fat loss, don’t eat carbohydrates immediately before or during cardiovascular exercise. Even if your only goal is fat loss, it is important to include weight training as part of your exercise program. Also, don’t restrict calories too much and be sure to get plenty of protein in your diet to help prevent muscle loss while burning fat. Consume a low fat diet to ensure that the fat you burn during your aerobic exercise is body fat and not dietary fat.
Scientific Background
Last month I explained the concepts of VO2 max and the lactate threshold. These are simply scientific ways of measuring cardiovascular fitness. Briefly, VO2 max is the body’s maximum rate of oxygen consumption (1,2). This determines the maximal intensity of aerobic exercise which you can sustain. The lactate threshold is the percentage of VO2 max at which lactic acid first appears as a waste product in the blood (1,2). Lactic acid is a byproduct of anaerobic metabolism when glucose is broken down without oxygen. Thus the terms “lactate threshold” or “anaerobic threshold” are often used interchangeably. This represents the rate of energy production which can be sustained aerobically before the anaerobic pathways kick in. These concepts may sound complicated but a simple example will make them clear. Let’s take a sedentary person who hasn’t exercised in years and put him on a training program. Initially he can only ride the stationary bike for 20 minutes at low intensity because he’s so out of shape. After six months of consistent training he can ride for 20 minutes at high intensity. He has just increased his VO2 max, his maximal level of sustainable exercise. At the beginning of his training program if he tried to peddle against high resistance, after a few minutes his thighs would begin to burn and ache from lactic acid accumulation. After six months of training he can peddle for 20 minutes against high resistance with no thigh pain. He has just increased his lactate threshold.
An aerobic exercise training program will increase both VO2 max and anaerobic threshold. What does this mean? The meaning of an increase in VO2 max is pretty obvious: it means you can exercise harder. An increase in anaerobic threshold means that you can exercise at a higher percentage of your maximal ability before anaerobic metabolism begins to contribute to energy production. So not only can a trained athlete exercise harder, he can exercise more efficiently. He can exercise at a higher percentage of his maximal ability before the lactic acid burn begins to set in. That implies he can maintain a higher percentage of his maximal output for a longer time before reaching fatigue. So now you can see that VO2 max and anaerobic threshold describe somewhat different aspects of endurance performance.
Another fundamental concept we need to understand is the respiratory quotient (RQ). This is defined as the ratio of carbon dioxide produced to oxygen consumed during energy production (1,2). What does this have to do with anything? It has everything to do with fat loss and body composition. Respiratory quotient is measured by analyzing the amount of oxygen a person extracts from the air and the amount of carbon dioxide he exhales into the atmosphere as he breathes. We can learn some very interesting things using this technique. It turns out that if a person is burning pure carbohydrate as his energy source the respiratory quotient is 1.0. If he is burning fat as his fuel source the respiratory quotient is 0.7. This difference comes from the fact that the carbon atoms in carbohydrate molecules are already partially oxidized (the carbon atoms are bound to oxygen in the sugar molecule). In fatty acids the carbon atoms are bound to hydrogen, and are said to be “reduced” (the chemical opposite of oxidized). It makes sense then that fat should contain more calories per gram than sugar, because in sugar the carbon atoms are already partially oxidized before you eat it. In a fatty acid molecule the carbon atoms are not oxidized at all, so when they are burned inside cells more energy is released per carbon atom than for glucose. Also, since the carbohydrate molecule already contains some oxygen atoms built into it, it takes fewer molecules of oxygen to complete its oxidation than for a fat molecule. This is the reason burning fat as your fuel source results in a different respiratory quotient than burning carbs. A typical mixed diet containing protein, carbs, and some fat results in a RQ around 0.8.
Whew! So what does this have to do with bodybuilding and fat loss? By measuring the RQ of people while they are exercising we can determine the fuel substrate which is being used. At rest and during sleep mostly fat is used as the body’s fuel source. During low intensity exercise, such as walking or low intensity biking, still mostly fat is used. At the other extreme, during very high intensity exercise such as weight lifting the predominant fuel source is carbohydrate. And at moderate exercise intensity a mixture of fat and carbs is used for fuel. If you think about the biochemical pathways of energy production this makes perfect sense. High intensity exercise like weight lifting is primarily fueled by the anaerobic pathway. This is because the muscle’s demand for energy is so high that oxygen cannot be supplied to the muscle fast enough to keep up with the demand, so the muscle has to turn to anaerobic metabolism. Anaerobic metabolism can supply rapid bursts of energy very quickly, but cannot be sustained for a very long time. This is why you can ride the bike for hours but can only do squats for about a minute before you fatigue. The body can use carbohydrate as a fuel for anaerobic energy production (glucose is converted to pyruvate in the glycolytic pathway and pyruvate is subsequently converted to lactate). However, there is no such thing as anaerobic fat metabolism. Fat requires oxygen to be converted to usable energy. Simply put, you can’t burn fat fast enough to keep up with the rigorous energy demands of intense weight lifting, so you have to use carbs. On the other hand, the oxidation of fat makes the perfect energy source for lower intensity exercise such as walking.
Many people use this rationale to advocate low intensity exercise (such as walking) as the ultimate exercise for fat loss. At first thought, this makes good sense. It is true that during low intensity exercise a higher percentage of the energy expended is derived from fat. The problem is that during low intensity exercise you burn very few calories, so even if almost all of the calories are derived from fat, that’s still not much fat loss. During moderate intensity aerobic exercise, such as jogging or a brisk bike ride against moderate resistance, a higher percentage of the calories you burn come from carbs, but you burn so many more total calories that the overall result is still greater fat loss. So it’s not just the percentage of energy derived from fat that’s important, but also how many total fat calories you burn. If you do your aerobics at moderate to high intensity you will burn more carbs along with the fat, but you’ll end up burning a greater amount of fat in the long run because you expend more calories.
To put this in perspective, don’t let me leave you with the wrong message. Walking is a great exercise for fat loss, it’s just that you’ll have to walk for hours everyday to see really noticeable results. I’m not against walking, I just don’t think it’s the best choice for serious fat loss. Just as there are plateaus you encounter while gaining muscle, you will also hit plateaus during fat loss. Probably the best way to stimulate accelerated fat loss is to increase the intensity of your aerobics. In your own experience, who’s leaner - the guy who walks three miles a day or the guy who runs three miles a day? The runners I know are leaner than the walkers. I’ve worked with a lot of bodybuilders who could never really get into contest shape until they started running.
Last month I talked about some of the metabolic adaptations that occur as a result of endurance training. One is an increase in the vascular supply to muscles. The harder the muscles are forced to work, the more blood they need. Another important adaptation is an increase in the fat-burning capacity of muscle cells. Endurance training causes an increase in the cellular content of mitochondria and enzymes responsible for burning fat. I don’t think you get much of a metabolic adaptation to low intensity exercise. Sure, you can burn fat if you walk long enough, but you really won’t increase your capillary density or beef up your fat-burning enzyme pathways significantly unless you train hard. The concept of intensity applies to endurance training just like it does to resistance training. If you want to see a big change in your body you have to force it to adapt by providing an intense training stimulus. If you still don’t believe me, just try it. It won’t cost you anything and you have nothing to lose. Try doing low intensity aerobics for a month (walking) and measure your body composition before and after. Then do moderate to high intensity aerobics for a month (jogging or fairly strenuous biking) and again measure your body composition. You’ll see. I’ve done this kind of thing with competitive bodybuilders about a zillion times, so I know what will happen.
Practical Applications
How do we put this all together to get the best results? Do moderate to high intensity aerobics for 30 to 60 continuous minutes a minimum of three days a week, and seven days a week is better. You should be breathing hard and sweating. Remember, fat metabolism requires oxygen. If you’re not breathing hard you’re not consuming much oxygen and so you can’t be burning much fat. It’s not that complicated. What about heart rate? If you want to measure heart rate, that’s fine. Probably between 70-85% of your theoretical maximum heart rate is a good goal to both burn fat and accrue the metabolic adaptations of endurance training (increased capillary density and increased fat-burning machinery). Your theoretical maximum heart rate is 220 minus your age. This is a pretty crude way to do it however because how your heart rate responds to exercise depends on your level of training.
Do your aerobic exercise for at least 30 minutes per session. It takes a while to liberate fatty acids from adipose tissue and really start burning much fat. You probably don’t burn much fat until about 15 minutes or so into the exercise session. Do your aerobics on an empty stomach. First thing in the morning before breakfast is a great time. Then your glycogen levels are somewhat depleted from your overnight fast and insulin levels are low. Since insulin blocks fat metabolism, aerobic exercise right after eating carbs is a bad idea. No carb drinks before or during your aerobics. Another good time to do your aerobics is right after weight training. The weight training depletes your glycogen levels so your body will be forced to burn fat instead of carbs. Also, weight training increases catecholamine levels (epinephrine and norepinephrine) which stimulate fat metabolism. So you’ll start burning fat right from the start of your aerobic exercise session that way.
The particular type of exercise you do doesn’t matter. Running, rowing, biking, stair climbing, skiing, in-line skating, and aerobics classes are all okay. Pick something you like and can stick with. I suggest mixing it up for variety. Just make sure you are breathing hard and try to work up a sweat. One technique to help keep the intensity up is circuit aerobics. Five minutes on the stair climber, five minutes on the treadmill, five minutes on the bike, and five minutes on the rowing machine, then repeat the circuit.
So we’ve covered the type of exercise, the training intensity, the training duration, the training frequency, and the timing of the training session. I can’t close without talking a little about nutrition. There are four key points I’d like to make. First, don’t cut calories too much. If you are faithful to the diet as outlined in the Nutrition Manual, you probably won’t have to cut calories at all. If you eat according to the diet, do your weight training, and do your aerobics, you will automatically get lean without having to cut calories. If you do need to reduce calories, do so very modestly. Ten percent below your maintenance requirement is plenty. If you reduce calories too drastically you will lose muscle, and thereby decrease your metabolic rate and your ability to burn fat. Remember, muscle is the engine that burns fat. Maintaining muscle mass is a priority. Second, eat a low fat diet. The aerobics program as described here is designed to maximize fat burning. If you don’t eat any fat in your diet, then the fat you burn during your aerobics has to come from stored body fat. If you have much fat in your diet then when you exercise you’ll simply burn the fat you just ate. You’ll be spinning your wheels and won’t get leaner. If you burn fat during exercise, but don’t eat fat, then you’ll have to lose body fat. It’s that simple. Third, get plenty of protein. This is key to preserving muscle mass while losing fat. During aerobic exercise, especially at high intensity, some of the fuel is derived from amino acids. This can result in muscle loss if you’re not careful. I’ve had very good results using a scoop of Hi-Protein powder before aerobics. This supplies very little carbohydrate and does not raise insulin levels significantly. The Hi-Protein increases the blood levels of amino acids, so that any aminos which are oxidized during the exercise session are derived from the protein powder instead of being extracted from muscle tissue. Here’s the strategy: if you exercise in the morning, get up and have a cup of coffee and a scoop of Hi-Protein powder, then do your aerobics. If you do your cardio work after weight training, then have a scoop of Hi-Protein between the weight training and the aerobics. This will prevent any loss of muscle tissue and will not inhibit fat metabolism. Fourth, follow your body composition. All serious bodybuilders follow their percent body fat and lean body mass. You have to in order to know what’s going on with your body composition. Scale weight is just not enough. The Body-Stat Kit is an invaluable tool in this regard. It includes a detailed manual that explains how to modify your diet and exercise to keep things moving in the right direction, and discusses specific problems commonly encountered while dieting for contests.
Parrillo Performance. We’re here to show you how.
Parrillo Performance Products
(800) 344-3404
References
1. McArdle WD, Katch FI, and Katch VL. Exercise Physiology: Energy, Nutrition, and Human Performance. Lea & Febiger, Philadelphia, 1991.
2. Wilmore JH and Costill DL. Physiology of Exercise and Sport. Human Kinetics, Champaign, IL, 1994.
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