Dieta i trening - po jakim czasie przyjdą efekty ?

wiara wprawdzie podobno czyni cuda ale rozum czyni ich pojawienie się bardziej prawdopodobnymi

oszz ty Tyko

tak to juz jest, ze jedni maja wiedze a inni swoje 'wygodne prawdy'

a coś poza tym?
podaj proszę źroodła swojej wiedzy - może skorzystamy

zrodla? no prosze bardzo- lekarze, kolarze, instruktorzy fitness

badania, konkretne nazwiska - teklefony jak mozesz
zadzownimy pogadamy i sama zobaczysz...

Użycie poszczególnych substratów jako źródeł energii w telegraficznym skrócie :

* Metabolism is the sum of all chemical reactions with living cells to provide energy for vital processes.
* At rest, 33% of the body's energy comes from carbohydrates, or glycogen, stored within the muscles and liver. 66% comes from fat.
* During aerobic work, 50-60% of the energy comes from fats
o Primarily carbohydrates are used during the first several minutes of exercise
o For an average fit person, it takes 20 to 30 minutes of continuous aerobic activity to burn 50% fat and 50% carbohydrate
o There is approximately a 7 fold increase of fat mobilization after 1 hour of exercise
* Proteins contribute less than 2% of the substrates used during exercise of less than 1 hour.
o Slightly more proteins are utilized as a fuel source during prolonged exercise.
+ During the final moments of exercise lasting 3 to 5 hours, protein utilization may reach 5-15% of the fuel supply (Berg A & Keul J 1980; Cerretelli P 1977; Hood D & Terjung R 1990; Lemon P & Mullin F 1980; Lemon P & Nagle 1980)
o Protein can supply up to 10% of total energy substrate utilization during prolonged intense exercise if glycogen stores and energy intake is inadequate (Brooks, 1987)
* The more fit an individual, the more they use fats over carbohydrates in the diet
o Reaches steady state sooner, and stays there longer
o Sympathetic stimulation mobilizes FFA
* On a low carbohydrate diet, you burn a higher proportion from fat
o Endurance can be reduced up to 50% until body adapts
o Adaptation to a low carbohydrate diet is possible if calories from protein and fat are sufficient
o If calories are not sufficient, lean tissue (muscle) is utilized by gluconeogenesis (conversion of protein to glucose)
* Low intensity, high duration aerobics
o Low intense exercise (<30% VO2 max) relies primarily on fat whereas high intense exercise (>70% VO2 max) primarily utilized carbohydrate.
o Higher proportion of fat is expended (not necessarily more fat)
+ Lower intense submaximal exercise utilizes proportionally less carbohydrates
o During low intense exercise prolonged exercise (ie greater than 30 minutes), a gradual shift from carbohydrate to fat metabolism occurs (Ball-Burnett MH, Green H & Houston M, 1991; Gollnick & Saltin B, 1988; Ladu M, Kapsas H & Palmer W, 1991; Powers S, Riley W, & Howley 1980)
* High intensity, low duration aerobics
o More calories burned in less time
o More carbohydrates, or glycogen utilized
+ Lactate threshold
# Sedentary: 70-75% max heart rate
# Trained: 80-90% max heart rate or higher
+ Intense or prolonged exercise can rapidly deplete muscle glycogen
o Carbohydrates are used as a fuel source when more type II muscle fibers are recruited.
+ Type II muscle fibers have an abundance of glycolytic enzymes but few mitochondreal and lipolytic enzymes.
o Increased blood levels of epiniphrine also increase the metabolism of carbohydrates.
+ High levels of epinephrine increase muscle glycogen breakdown, glycolysis and lactate production (Brooks G & Mercier J 1994).
o Greater lactate production inhibits fat metabolism (Turcotte L, et al. 1995)
o More fat metabolized hours intense exercise (Mulla, et al., 2000) (Phelain, et al., 1997)
* Weight training, plyometrics, sprinting, or high intense interval training
o "It is known that the energy needs for sustaining maximal exercise of very short duration are largely met by the creatine phosphate breakdown such that its concentration decreases to almost zero at the end of maximal exercise leading to exhaustion. An almost complete creatine phosphate recovery is normally observed within rest periods lasting about 4 minutes following repeated maximal exercises of short duration." (Tremblay, et al., 1994)
o Primarily carbohydrates utilized (after limited ATP and CP stores)
o Fat is utilized many hours after anaerobic exercise

Aby poszerzyć swą wiedzę w tym temacie, na początek polecam lekturę :


Arner, P., E. Kriegholm, P. Engfeldt, and J. Bolinder (1990). Adrenergic regulation of lipolysis in situ at rest and during exercise. J. Clin. Invest. 85:893-898.

Ballor, D.L., J.P. McCarthy and E.J. Wilterdink (1990). Exercise intensity does not affect the composition of dietand exercise-induced body mass loss. Am J Clin Nutr. 51:142-146.

Costill, D.F., E.F. Coyle, G. Dalsky, W. Evans, W. Fink, and D. Hoopes. (1977). Effects of elevated plasma FFA and insulin on muscle glycogen usage during exercise. J. Appl. Physiol. 43: 695-699.

Coyle, E.F., A.R. Coggan, M.K. Hemmert, R.C. Lowe, and T.J. Walters (1985). Substrate usage during prolonged exercise following a preexercise meal. J. Appl. Physiol. 59:429-433.

Essen, B., L. Hagenfeldt, and L. Kaijser (1977). Utilization of blood-borne and intramuscular substrates during continuous and intermittent exercise in man. J. Physiol. 265:489-506.

Hurley, B.F., P.M. Nemeth, W.H. Martin, J.M. Hagberg, G.P. Dalsky, and J.O. Holloszy (1986). Muscle triglyceride utilization during exercise: effect of training. J. Appl. Physiol. 60:562-567. Issekutz, B., and B. Paul (1968). Intramuscular energy sources in exercising normal and pancreatectomized dogs. Am. J. Physiol. 215(1):197-204.

Jensen, M.D., M. Caruso, V. Heiling, and J.M Miles (1989). Insulin regulation of lypolysis in nondiabetic and IDDM subjects. Diabetes 38:1595-1601.

Jeukendrup, A.E., W.H.M. Saris, P. Schrauwen, F. Brouns, and A.J.M. Wagenmakers (1995). Metabolic availability of medium-chaim triglycerides coingested with carbohydrate during prolonged exercise. J. Appl. Physiol. 79: 756-762.

Kiens, B., B. Essen-Gustavsson, N.J. Christensen, and B. Saltin (1993). Skeletal muscle substrate utilization during submaximal exercise in man: effect of endurance training. J. Physiol. (London) 469: 459-478.

Klein, S., E.F. Coyle, and R.R. Wolfe (1994). Fat metabolism during low-intensity exercise in endurance-trained and untrained men. Am. J. Physiol. 267 (Endocrinol. Metab. 30):E934-E940. Mackie, B.G., G.A. Dudley, H. Kaciuba-Uscilko, and R.L. Terjung (1980). Uptake of chylomicron triglycerides by contracting skeletal muscle in rats. J. Appl. Physiol. 49: 851-855.

Martin, W.H., G.P. Dalsky, B.F. Hurley, D.E. Matthews, D.M. Bier, J.O. Hagberg, and J.O. Holloszy (1993). Effect of endurance training on plasma FFA turnover and oxidation during exercise. Am. J. Physiol. 265 (Endocrinol. Metab. 28):E708-E714.

Montain, S.J., M.K. Hopper, A.R. Coggan, and E.F. Coyle (1991). Exercise metabolism at different time intervals after a meal. J. Appl. Physiol. 70(2):882-888.

Morgan, T.E., F.A. Short, and L.A. Cobb (1969). Effect of long-term exercise on skeletal muscle lipid composition. Am. J. Physiol. 216:82-86.

Oscai, L.B., D.A. Essig, and W.K. Palmer (1990). Lipase regulation of muscle triglyceride hydrolysis. J. Appl. Physiol. 69: 1571-1577.

Phinney, S.D., Bistrian, W.J. Evans, E. Gervino, and G.L. Blackburn (1983). The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 32:769-776.

Romijn, J.A., E.F. Coyle, L.S. Sidossis, A. Gastaldelli, J.F. Horowitz, E. Endert, and R.R. Wolfe (1993). Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration. Am. J. Physiol. 265 (Endocrinol. Metab. 28):E380-E391.

Simonsen, J.C., W.M. Sherman, D.R. Lamb, A.R. Dernbach, J.A. Doyle, and R. Strauss (1991). Dietary carbohydrate, muscle glycogen, and power during rowing training. J. Appl. Physiol. 70: 1500-1505.

Terjung, R. (1995). Muscle adaptations to aerobic training. Sports Sci. Exchange 8(54), Number 1.

Terjung,R.L. B. G. Mackie, G.A. Dudley, and H. Kaciuba-Uscilko (1983). Influence of exercise on chylomicron triacylglycerol metabolism: plasma turnover and muscle uptake. Med. Sci. Sports Exerc. 15: 340-347.

Turcotte, L.P., B. Kiens and E.A. Richter (1991). Saturation kinetics of palmitate uptake in perfused skeletal muscle. FEBS Letters 279: 327-329.

Vukovich, M.D., D.L. Costill, M.S. Hickey, S.W. Trappe, K.J. Cole, and W.J. Fink (1993). Effect of fat emulsion infusion and fat feeding on muscle glycogen utilization during cycle exercise. J. Appl. Physiol. 75: 1513-1518.

Wolfe, R.R., S. Klein, F. Carraro, and J.-M. Weber (1990). Role of triglyceride-fatty acid cycle in controlling fat metbolism in humans during and after exercise. Am. J. Physiol. 258

Zmieniony przez - Tyka w dniu 2005-04-20 10:42:36

I jeszcze małe kompendium wiedzy o aerobach :


Cardiovascular Exercise Principles and Guidelines

By: Chad Tackett

For maximum effectiveness and safety, cardiovascular exercise has specific instructions on the frequency, duration, and intensity. These are the three important components of cardiovascular exercise that you really need to understand and implement in your program. In addition, your cardiovascular program should include a warm-up, a cool-down, and stretching of the primary muscles used in the exercise. This article is part one of a two part series discussing the very important principles and guidelines of a safe and effective cardiovascular exercise program. Part one will explain the proper methods of warming-up, stretching, and cooling-down and discuss the frequency and duration of a sound cardiovascular routine. Part two will discuss how to monitor exercise intensity and heart zone training.

Warming Up and Stretching: One very common mistake is stretching before muscles are warmed-up. It is important to stretch after your muscles are warm (after blood has circulated through them). Never stretch a cold muscle. First warm up.
A warm-up should be done for at least 5-10 minutes at a low intensity. Usually, the warm-up is done by doing the same activity as the cardiovascular workout but at an intensity of 50-60% of maximum heart rate (max HR). After you've warmed-up for 5-10 minutes at a relatively low intensity, your muscles should be warm. To prevent injury and to improve your performance, you should stretch the primary muscles used in the warm up before proceeding to the cardiovascular exercise.

Cooling Down: The cool down is similar to the warm-up in that it should last 5-10 minutes and be done at a low intensity (50-60% of max HR). After you have completed your cardiovascular exercise and cooled-down properly, it is now important that you stretch the primary muscles being used. Warming-up, stretching, and cooling-down are very important to every exercise session. They not only help your performance levels and produce better results, they also drastically decrease your risk of injury.

Frequency of Exercise: The first component of cardiovascular exercise is frequency of the exercise, which refers to the number of exercise sessions per week. To improve both cardiovascular fitness and to decrease body fat or maintain body fat at optimum levels, you should exercise (cardiovascularly) at least three days a week. The American College of Sports Medicine recommends three to five days a week for most cardiovascular programs. Those of you who are very out of shape and/or who are overweight and doing weight-bearing cardiovascular exercise such as an aerobics class or jogging, might want to have at least 36 to 48 hours of rest between workouts to prevent an injury and to promote adequate bone and joint stress recovery.

Duration of Exercise: The second component of cardiovascular exercise is the duration, which refers to the time you've spent exercising. The cardiovascular session, not including the warm-up and cool-down, should vary from 20-60 minutes to gain significant cardiorespiratory and fat burning-benefits. Each time you do your cardiovascular exercise, try to do at least 20 minutes or more. Of course, the longer you go, the more calories and fat you'll "burn" and the better you'll condition your cardiovascular system. All beginners, especially those who are out of shape, should take a very conservative approach and train at relatively low intensities (50-70% max HR) for 10-25 minutes. As you get in better shape, you can gradually increase the duration of time you exercise.

It is important that you gradually increase the duration before you increase the intensity. That is, when beginning a walking program for example, be more concerned with increasing the number of minutes of the exercise session before you increase the intensity, by increasing your speed or by walking hilly terrain.

You learned that cardiovascular exercise should be done a minimum of three times a week, a minimum of 20 minutes per session and should be done after a 5-10 minute warm-up (at a low intensity of 50-60% of max HR) and a 5-10 minute cool-down (at a low intensity of 50-60% of max HR) should follow. Once your muscles are warm (after warm up) and after the cardiovascular exercise, you should stretch those muscles used in the exercise.

There are two ways in which you can check your heart rate during exercise. The most accurate one is to purchase a heart-rate monitor that you strap around your chest. It will give you feedback on a digital watch that tells you exactly what your heart rate is at a specific time in the exercise session. The other way to obtain your heart rate is by palpating (feeling) either the carotid artery, the temporal artery, or the radial artery. The easiest site is either the cartoid or the radial artery. The cartoid artery may be felt by gently placing your index finger on your neck, between the middle of your collar bone and jaw line. Palpating the radial artery is done by placing your index and middle finger on the underside and thumb-side of your wrist.

When you're taking your heart rate you measure it in beats per minute (counting the number of beats for 60 seconds). For convenience, many people take their pulse for 6 seconds and multiply that number by 10, or simply add a 0 behind the number just obtained. So, if in 6 seconds you counted 12 beats, that would mean your heart rate was 120 beats per minute (bpm). Although counting for 6 seconds is most convenient, keep in mind that the longer the time interval used, the more accurate the results will be. For example, counting your heart rate for 30 seconds and then multiplying that number by 2 will give a slightly more accurate reading than counting your heart rate for 15 seconds and multiplying by 4, or 10 seconds and multiplying by 6. What ever time interval you use, be consistent.

Heart Zone Training: How do you know if you are training too intensely or not intensely enough for what you want to achieve? This is where Heart Zone Training comes in. Refer to the chart below. The top of the chart reads "Maximum Heart Rate," which is 100% of your heart rate (the fastest your heart will beat). This is different for everyone. To use Heart Zone Training you must first determine your maximum heart rate (max HR).


You can determine your max HR one of two ways. One way is to use the age predicted max HR formula, whereby you subtract your age from 220. So, if you are 40 years old, your predicted max HR would be 180 bpm. The other method, which is much more accurate and more individualized, is actually having a medical or fitness professional administer a max HR test for you, which is usually done on a stationery bicycle or treadmill for several minutes and requires very hard work. Thus, only those cleared by a physician should do this test. We do not explain how to administer this test because only trained professionals should do so. Please refer to the Global Health and Fitness Personal Training Directory for professionals in your area (may or may not be trained in administering a max HR test).

Once you have determined your max HR, you will need to decide what zone you want to train at. As you can see, there are five different training zones separated by 10% increments, each having different characteristics and benefits.


Healthy Heart Zone: The first zone is called the Healthy Heart Zone. This is 50-60% of your max HR. This is the easiest and most comfortable zone within which to train and is the one that is best for people who are just starting an exercise program or have low functional capacity. Those of you who are walkers most likely train at this zone. Although this zone has been criticized for not burning enough total calories, and for not being intense enough to get great cardiorespiratory benefits, it has been shown to help decrease body fat, blood pressure and cholesterol. It also decreases the risk of degenerative diseases and has a low risk of injury. In this zone, 10% of carbohydrates are "burned" (used as energy), 5% of protein is burned and a whopping 85% of fat is burned.


Fitness Zone: The next zone is the Fitness Zone, which is 60-70% of your max HR. Once again, 85% of your calories burned in this zone are fats, 5% are proteins and 10% are carbohydrates. Studies have shown that in this zone you can condition your fat mobilization (getting fat out of your cells) while conditioning your fat transportation (getting fat to muscles). Thus, in this zone, you are training your fat cells to increase the rate of fat release and training your muscles to burn fat. Therefore, the benefits of this zone are not only the same as the healthy heart zone training at 50-60% but you are now slightly increasing the total number of calories burned and provide a little more cardiorespiratory benefits. You burn more total calories at this zone simply because it is more intense.


Aerobic Zone: The third zone, the Aerobic Zone, requires that you train at 70-80% of your max HR. This is the preferred zone if you are training for an endurance event. In this zone, your functional capacity will greatly improve and you can expect to increase the number and size of blood vessels, increase vital capacity and respiratory rate and achieve increases in pulmonary ventilation, as well as increases in arterial venous oxygen. Moreover, stroke volume (amount of blood pumped per heart beat) will increase, and your resting heart rate will decrease. What does all this mean? It means that your cardiovascular and respiratory system will improve and you will increase the size and strength of your heart. In this zone, 50% of calories burned are from carbohydrates, 50% are from fat and less than 1% is from protein. And, because there is an increase in intensity, there is also an increase in the total number of calories burned.


Anaerobic Zone: The next training zone is called the Threshold or Anaerobic zone, which is 80-90% of your max HR. Benefits include an improved VO2 maximum (the highest amount of oxygen one can consume during exercise) and thus an improved cardiorespiratory system, and a higher lactate tolerance ability which means your endurance will improve and you'll be able to fight fatigue better. Since the intensity is high, more calories will be burned than within the other three zones. Although more calories are burned in this zone, 85% of the calories burned are from carbohydrates, 15% from fat and less than 1% are from protein.


Red-line Zone: The last training zone is called the Redline Zone, which is 90-100% of your max HR. Remember, training at 100% is your maximum heart rate (maximum HR), your heart rate will not get any higher. This zone burns the highest total number of calories and the lowest percentage of fat calories. Ninety percent of the calories burned here are carbohydrates, only 10% are fats and again less than one percent is protein. This zone is so intense that very few people can actually stay in this zone for the minimum 20 minutes, or even five minutes (you should only train in this zone if you are in very good shape and have been cleared by a physician to do so). Usually, people use this zone for interval training. For example, one might do three minutes in the Aerobic Zone and then one minute in this Redline Zone and then back to the Aerobic Zone.


Overcoming Cardiovascular Exercise Plateaus: Cardiovascular exercise should be done a minimum of three times a week, a minimum of 20 minutes per session and intensity should be between 50-85% of your maximum heart rate (max HR). Your heart rate should be monitored by either the palpating method of checking your heart rate or by using a heart rate monitor. People of low functional capacity (out of shape) who are just starting out should begin training at a low intensity, probably between 50-65% of their max HR. All cardiovascular exercises should be done after a 5-10 minute warm-up (at a low intensity of 50-60 percent of your max HR) and a 5-10 minute cool-down (at a low intensity of 50-60 percent of your max HR) should follow. Once your muscles are warm (after warm up) and after the cardiovascular exercise, you should stretch those muscles used in the exercise. For example, after bicycling, stretch your quadriceps, hamstrings, calves, hips, and low back. After doing the rowing machine, stretch your legs, back, biceps, and shoulders.

It is important that you understand and implement the different methods of cardiovascular exercise into your program. It's critical that you realize the different options of a cardiovascular program so you can overcome any plateaus you encounter and prevent boredom. Both eventually happen if you continue to do the same exercise and the same training style. You should always be going through a "momentum phase" in your cardiovascular exercise program where you continue to achieve good results. Thus, when you reach a plateau, you want to change your routine and implement a new method. I will now discuss the three different training methods that you should work into your cardiovascular exercise program.


Continuous Training: The first method, the most common and traditional way of doing cardiovascular exercise, is called continuous training This means that you do one form of cardiovascular exercise for the full duration. So your entire cardiovascular exercise session is one continuous activity, such as riding a stationary bike. As a result you're using large muscle groups (your legs) continuously for at least 20 minutes at 50-100 percent of your max HR intensity. You may get bored with this and want to increase the intensity, so the next method will be something to eventually incorporate into your program.


Interval Training: Interval training is an intermediate method of cardiovascular training and thus should not be done by beginners or those of low functional capacity. Interval training consists of repeated intervals of relatively light intensities such as walking interspersed with relatively hard intensities such as jogging or running. The "light" interval should be done at an intensity ranging from 50-70 percent of your max HR, depending on functional capacity and personal goals and interests. The "hard" interval should be done at an intensity ranging from 70-100 percent of your max HR (you should first get cleared by your physician to train at an intensity greater than 80 percent of max HR), depending on functional capacity and personal goals and interests. The light interval, or the walking interval in this example, should take approximately the same time to complete as the hard or jogging/running interval. Intervals typically last 2-10 minutes in duration. Many times, however, the light interval lasts longer than the hard interval, especially for those of low functional capacity or those of high functional capacity training at an intensity greater than 80 percent of max HR). These intervals should be repeated until you have reached the desired duration, usually 20-60 minutes.

Please note: before doing your interval training, start with a warm-up of the same cardiovascular activity for about 5-10 minutes at 50-60 percent of max HR, stretch the muscles used, then begin your light interval, hard interval, and so on. For example, if you are in moderate shape and you want to train cardiovascularly for 30 minutes, you should: begin with a warm-up of the same activity (walking in this example) for 5-10 minutes at a light intensity (50-60 percent of your max HR); do a light interval of walking slowly, increasing the intensity for about 5 minutes; do a hard interval by either jogging or running for about 5 minutes. Do this two more times and you have completed your cardiovascular workout and trained at several different heart rate zones, gaining several different benefits. Be sure to cool-down for 5-10 minutes at a light intensity of 50-60 percent of your max HR. Stretch the primary muscles used.


Composite Training: The third training method is called composite training. This is a combination of several different cardiovascular exercises, one after the other. One example is bicycling 15 minutes (after a warm-up and stretching the muscles used) to a track or running course, running or jogging 10-15 minutes, then bicycling back home, followed by a cool-down and stretching those muscles used. Or, if you work out in a health club, you could walk on a treadmill for 10 minutes (after warm-up and stretching the muscles used) and do the stairstepper for an additional 10 minutes. If you're shooting for 30 minutes total in duration, you could then go right to the rowing machine and finish with a final 10 minutes, followed by a cool-down and stretching the same muscles as before. This is another way of fighting boredom and also increasing the intensity and results.

If you want to take it one step further and really try something intense and exciting, incorporate the interval and the composite training. While you're on the treadmill change the speed from walking to jogging every other minute, or from flat to a 5 percent grade. Then, after 10 minutes of treadmill, move on to the stationary bike changing the resistance from intense to less intense, every other minute. Remember, always begin with a warm-up of 5-10 minutes at a low intensity and stretch the muscles used, and conclude your workout with a cool-down of 5-10 minutes at a low intensity of 50-60 percent of max HR. Stretch the same muscles as before


Cardiovascular Exercise Safety Precautions: Cardiovascular exercise has received a lot of attention over the last 15 years as the centerpiece of physical fitness, weight management, and cardiorespiratory (heart and lung) health. The terms cardiovascular exercise, cardiorespiratory fitness and aerobic exercise are all synonymous. This kind of exercise requires large muscle movement over a sustained period of time, elevating your heart rate to at least 50% of maximum level. Examples include walking, jogging, biking, swimming, and any other repetitious activity that can be performed over an extended period of time.

Cardiovascular exercise has numerous benefits. They include a decreased blood pressure, increased HDL (good) cholesterol (high-density lipoproteins responsible for removing LDL (bad) cholesterol from the cells in the arteries and transporting it back to the liver for removal from the body), decreased LDL cholesterol, decreased body fat, decreased glucose-stimulated insulin secretion (this increases capillary density and blood flow to active muscles), increased heart and lung function and efficiency, and decreased anxiety, tension, and depression.

All of these benefits combine to help lower your risk of cardiovascular disease by reducing risk factors like obesity, hypertension, and high blood cholesterol. In addition, cardiovascular exercise serves as a foundation for the activities of daily living, sports, and other outdoor activities. Activities such as tennis, golf, skiing, dancing, basketball, volleyball, boxing, hiking, and strength training programs all benefit from cardiovascular exercise. Your enjoyment of day-to-day and physical activities will also greatly benefit because you will have more stamina, less fatigue and less risk of injury.

However, there are several precautions you should take to help maximize exercise safety.

Post-meal Exercise: Cardiovascular exercise soon after a full meal can compromise oxygen and nutrient delivery to the working muscles, and cause gastric discomfort. Thus, you should wait at least 60-90 minutes after a full meal before engaging in cardiovascular exercise. The level of exercise and the amount and type of food consumed affect the time required for digestion to be completed before beginning exercise. The higher the exercise intensity and/or the greater the amount food consumed, the longer the time should be between eating and exercising.


Exercising in Hot Weather: Another factor that increases the risk of injury and complications is exercising in hot weather. The following are guidelines to prevent heat stress: 1. Allow 1-2 weeks for acclimatization to a hot environment 2. Avoid training in the hottest part of the day, usually between 10 a.m. and 4 p.m., during the summer. 3. Drink water before, during and after exercise. During prolonged cardiovascular exercise, drink 4-6 ounces of fluids (preferably water) every twenty minutes. 4. Wear loose-fitting clothes that allow for evaporation of sweat. 5. Decrease training intensity by monitoring heart rate in hot environments. 6. Take a 10-15 minute rest for every 45-60 minutes of physical activity. 7. Give special consideration to, and use caution if you are a heat-sensitive person (obese, unfit, history of heat stroke, etc.).


Pollutants: Have an adverse effect on the body in many ways. This is of concern if you exercise outdoors in or near big cities. Some common ones include ozone, carbon monoxide, and sulfur dioxide. The most problematic of these pollutants is ozone, or smog, which is caused by the combination of ultraviolet light and emissions from internal combustion engines. Ozone exposure may impair lung function during cardiovascular exercise. Carbon monoxide is another common air pollutant that can reduce exercise safety and effectiveness. This is caused by exposure to crowded freeways or smoke filled rooms. Sulfur dioxide is not a major irritant for most people, but those with asthma or bronchospasms tend to be adversely affected by it.

Cardiovascular exercise provides many important benefits that cannot be achieved by any other exercise or activity. Cardiovascular exercise is also very convenient; you can do it in the outdoors or inside while watching television or reading a book. However, when enjoying this great form of physical activity, be sure to adhere to these precautions so that your program is not only effective, but safe as well. Good luck: I hope you enjoy all the wonderful benefits of a safe and effective cardiovascular exercise program.

Chad Tackett, the President of Global Health and Fitness (GHF), has degrees in Exercise and Heath Science and Nutrition, is a Certified Personal Trainer, and is a regular guest lecturer to both professional and lay audiences on the principles of effective exercise and eating habits.

I jeszcze parę słówek na temat spalania tłuszczu w czasie ćwiczeń, również w zależności od diety i wybranych suplementów


Fat Burning During Exercise: Can Ergogenics Change the Balance ?
John A. Hawley, PhD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 9 - SEPTEMBER 98

In Brief: Endurance athletes and dieters are eager to burn more fat during exercise; athletes hope to conserve carbohydrate stores, while dieters wish to decrease fat stores. This article briefly reviews the role of fat as an energy source for physical activity, discusses how exercise intensity and duration affect fat and carbohydrate metabolism, and assesses the nutrition strategies athletes are most likely to use in attempts to promote fat burning during exercise: caffeine ingestion, L-carnitine supplements, medium-chain triglyceride supplements, and high-fat diets. Of this group, caffeine ingestion is the only strategy scientifically proven to enhance athletic performance.

In recent years, a multitude of dietary supplements and nutrition strategies have been promoted as "magic bullets" to boost fat metabolism, reduce body fat, and improve athletic performance. Though some of these substances may enhance exercise capacity and, in particular, fat metabolism, most claims are based on anecdote, testimony, and inventive marketing, rather than sound science.

The search for strategies to improve athletic performance has prompted a recent surge of interest in nutrition practices that, in theory, could promote fatty acid oxidation, slow carbohydrate utilization, and improve exercise capacity. However, most of these interventions have little or no scientific basis and should not be recommended for use by healthy individuals or athletes to improve exercise performance.

Fat as an Energy Source

Compared with the body's limited carbohydrate stores, triglyceride reserves are plentiful. In a healthy, untrained individual, between 70,000 and 100,000 kcal of energy is stored as fat, mainly in the peripheral adipocytes. Even highly trained athletes who have little adipose tissue have fat stores that far exceed their athletic requirements. Although most fat is stored in adipose tissue, endurance athletes have small but physiologically important amounts of triglyceride within muscle cells; active muscle mass may contain up to 300 g of fat, most stored within the myocyte as small lipid droplets.

As a stored source of energy, fat has an advantage over carbohydrate: the energy density is higher while the relative weight is lower. Fatty acids provide more adenosine triphosphate (ATP) per molecule than glucose. However, to produce the equivalent amount of ATP, the complete oxidation of fatty acids requires more oxygen than the oxidation of carbohydrate.

Exercise Intensity and Fuel Use

The relative contributions of fat and carbohydrate to energy vary with exercise intensity. Low-intensity activities such as walking strongly stimulate lipolysis from peripheral adipocytes, while intramuscular triglycerides contribute little or nothing to total energy expenditure (1). The rate of carbohydrate use is also low: carbohydrate needs are met predominantly by circulating blood glucose, with little or no muscle glycogen breakdown (figure 1: not shown). The rate of appearance of fatty acids into the plasma peaks during low-intensity exercise (25% to 30% of VO2 max) and then declines as exercise intensity increases.

In contrast, the rate of fat oxidation is highest during moderate activity such as easy jogging (65% of VO2 max). At such an intensity, plasma free fatty acids and intramuscular triglyceride contribute equally to the overall rate of fat oxidation. During high-intensity exercise (85% of VO2 max), the rate of total fat oxidation falls, mainly because the appearance of fatty acids into the plasma is suppressed. At the same time, lipolysis of intramuscular triglycerides does not rise substantially when exercise intensity increases from 65% to 85% of VO2 max. This would not affect recreational athletes because most cannot sustain high-intensity exercise for more than 10 to 15 minutes without accumulating high (greater than 10 mM) concentrations of lactic acid in the working muscles and blood, which would cause discomfort and stop activity.

When low-intensity exercise continues more than 90 minutes, the pattern of substrate metabolism changes little relative to the first 20 to 30 minutes of exercise. The same is true of moderate-intensity exercise (65% of VO2 max): the rate of total fat or carbohydrate oxidation changes little after 2 hours of jogging or cycling at this intensity compared with the first 30 minutes. However, this level of exercise induces a progressive increase in the mobilization of fatty acids from peripheral adipocytes into the plasma (1). Therefore, the contribution of intramuscular substrates (triglyceride and glycogen) to total energy expenditure probably decreases when the duration of moderate-intensity exercise increases beyond 90 minutes.

Nutrition Tools to Change Metabolism

Endogenous carbohydrate reserves are limited, and muscle and liver glycogen depletion often coincides with fatigue during endurance events and many team sports (2). Consequently, methods that promote fatty acid oxidation and conserve carbohydrate stores might improve exercise capacity. Both endurance training and nutrition strategies are used in pursuit of this goal.

The effects of endurance training on fat metabolism are well documented: it enhances total fatty acid oxidation by increasing intramuscular triglyceride storage and maximal fatty acid flux. These processes conserve endogenous carbohydrate stores and prolong intense exercise.

As for nutrition strategies, many so-called ergogenic aids have been investigated for their potential to increase fat utilization. Among them are caffeine, L-carnitine, medium-chain triglycerides, and high-fat, low-carbohydrate diets.

Caffeine

The use of caffeine as a potential ergogenic aid is not new; the Medical Commission of the International Olympic Committee (IOC) first banned caffeine in 1962, rescinded the ban a decade later, and recently reclassified it as a restricted drug (an illegal dose is greater than 12 mg/L in urine). Most athletes consume caffeine as strong, black coffee; others take over-the-counter antidrowsiness preparations that contain caffeine.

Once ingested, orally administered caffeine is almost completely absorbed. Plasma caffeine concentration peaks about 45 to 60 minutes after a single 250-mg dose, although individuals vary in their response. Under normal ingestion regimens, it is highly unlikely that any individual could exceed the current IOC limit.

Caffeine affects almost every organ system, with the most obvious being the central nervous system. The stimulant increases alertness, reduces perceived effort during exercise, and decreases reaction time. At high doses (more than 15 mg/kg body weight), caffeine can also produce bradycardia, hypertension, nervousness, irritability, insomnia, and gastrointestinal distress (3).

In the first study (4) of caffeine as an ergogenic aid, a single dose (5 mg/kg body weight) ingested 60 minutes before exercise increased time to fatigue by 20% during intense cycling (80% of VO2 max) (4). Other laboratory (5) and field (6) studies confirmed the benefits of caffeine for endurance performance. The postulated mechanism for the improved exercise capacity was a rise in circulating free-fatty-acid concentration, an increase in fatty acid oxidation, and a reduction in carbohydrate utilization during exercise.

Evidence of a glycogen-sparing effect--most apparent during the early stages of exercise--has been found in every study that has determined muscular glycogen levels after caffeine ingestion (7,8). There is little doubt among scientists that caffeine positively affects fat metabolism, and that ingestion in legal quantities can improve performance in continuous, moderate-intensity exercise (submaximal exercise lasting more than 15 minutes) (3). When compared with placebo, caffeine (150 to 250 mg) has also been shown to improve 5-minute running and cycling performance in moderately or well-trained athletes who perform at or near their VO2 max (3). In contrast, caffeine has no ergogenic effect on maximal anaerobic (sprint) events lasting less than 30 seconds or maximal graded exercise to exhaustion (9).

L-Carnitine Supplementation

Carnitine plays a central role in the metabolism of fatty acids by transporting them from the cytosol to the mitochondrial matrix for beta oxidation. Long-chain fatty acid oxidation in all tissues is carnitine dependent; therefore, hereditary and acquired carnitine deficiencies cause triglyceride to accumulate in the skeletal muscles, impair fatty acid utilization, and reduce exercise capacity. Carnitine supplementation can usually reverse these changes (10).

It has been hypothesized that carnitine supplementation in healthy people increases fatty acid transport into the mitochondria and subsequent oxidation. If this were true, supplementation would significantly benefit endurance athletes and individuals wishing to lose weight.

The normal carnitine pool in a healthy 70-kg adult is about 100 mmol; more than 98% resides in skeletal and cardiac muscle, 1.6% in the liver and kidneys, and only 0.4% in the extracellular fluid (11). More than 50% of the daily need for carnitine is normally supplied by the diet from meat, poultry, fish, and some dairy products; the rest is endogenously biosynthesized from methionine and lysine. Daily urine losses are usually less than 2% of the total body carnitine store.

Many well-controlled studies have examined the effects of carnitine supplementation on metabolism and athletic performance in moderately trained individuals (12,13) and well-trained athletes (14,15). The doses used in these studies have varied from 2 to 6 g/day, and the length of supplementation from 5 days to 4 weeks. The results of these and many other investigations (16) convincingly demonstrate that carnitine supplementation has no effect on fuel utilization at rest (12) or during exercise (12,14).

Because supplementation does not alter lipid metabolism during exercise, it is not surprising that the rate of muscle glycogen utilization does not change (15). Lactate metabolism is not reduced (12,14) and blood pH does not change during submaximal (15) or maximal (14) exercise. Even when carbohydrate availability has been compromised before exercise by reducing muscle glycogen stores, carnitine supplementation still fails to alter lipid metabolism during submaximal exercise (17).

Because of carnitine's role in fatty acid metabolism, it is not surprising that it has been targeted as a potential promoter of fat loss. Carnitine is vigorously marketed to athletes in sports that require making weight or maintaining low body fat (wrestling, rowing, gymnastics, bodybuilding). However, there is no scientific evidence that carnitine enhances fatty acid oxidation, helps reduce body fat, or helps athletes "make weight."

Finally, many studies have shown little or no loss of carnitine from skeletal muscle during low- or high-intensity exercise (16), suggesting that training does not substantially reduce muscle carnitine levels in healthy athletes eating conventional diets. Massive doses of carnitine increase muscle carnitine levels by only 1% or 2% (18). Therefore, there is little or no reason for moderately active individuals or athletes in hard training to take carnitine supplements.

Medium-Chain Triglycerides

Medium-chain triglycerides contain predominantly fatty acids with a chain length of C6-10. Appreciable amounts of medium-chain triglycerides are not found in the diet. Compared with long-chain fatty acids, medium-chain triglycerides--when ingested with carbohydrate--are emptied very rapidly from the stomach and are absorbed almost as fast as glucose. Consequently, recent interest has focused on the potential ergogenic effect of ingesting medium-chain triglyceride solutions for endurance events.

The first investigators to compare the effects of medium-chain triglyceride ingestion to glucose during exercise (2 hours of cycling at 65% of VO2 max) found that the contributions to total energy requirements during exercise were similar (19). A more recent study (20) combined carbohydrate with medium-chain triglyceride during 3 hours of moderate-intensity (57% VO2 max) exercise in well-trained cyclists. About 70% of the triglyceride was oxidized when ingested with carbohydrate, compared to 33% when ingested alone. Toward the end of exercise, the rate of medium-chain triglyceride oxidation approached the rate of ingestion. Even so, the maximum contribution of ingested medium-chain triglycerides to total energy expenditure was only 7%.

In a separate study (21), the same researchers examined the effects of medium-chain triglyceride ingestion on the rates of muscle glycogen utilization during 180 minutes of moderate-intensity cycling. Ingesting medium-chain triglyceride (10 g/hr) did not affect the rate of total carbohydrate oxidation or the rate of muscle glycogen utilization. Even when subjects commenced exercise with low muscle glycogen, medium-chain triglyceride ingestion had no effect on carbohydrate utilization (21).

To date, only one study (22) has reported a beneficial effect of medium-chain triglyceride ingestion on performance. Large doses (about 30 g/hr) of medium-chain triglyceride in a carbohydrate solution improved performance 2.5% over a carbohydrate solution alone in a 40-km cycle time trial undertaken after 2 hours of moderate-intensity exercise (22). Researchers attributed the enhanced performance to the larger doses of medium-chain triglyceride used in this study relative to those used in studies that did not show an effect. The higher dose produced higher levels of fatty acids in the blood and, presumably, subsequent increased oxidation. As noted, however, this study is the exception. Moreover, ingestion of larger amounts (30 g/hr) is likely to produce gastrointestinal problems in most athletes, which would probably hurt performance.

High-Fat Diets

Altering an individual's diet 24 to 48 hours before exercise is a well-known, effective tool for modifying the patterns of substrate utilization and improving performance (2). Consuming a diet high in fat (greater than 60% of energy intake) and low in carbohydrate (less than 15% of energy) for 1 to 3 days significantly reduces resting muscle glycogen content, shifts exercise metabolism in favor of lipid oxidation, and impairs submaximal exercise capacity (23). On the other hand, some evidence suggests that longer (5- to 7-day) high-fat-diet periods may induce adaptations that "retool" the working muscle to increase its capacity for fatty acid oxidation (24).

The most frequently cited study (25) supporting the use of high-fat diets compared the effects of 28 days of a high-fat diet (85% of energy) with those of an isocaloric high-carbohydrate diet (66% of energy) on submaximal cycle time to exhaustion. Although the high-fat diet reduced resting muscle glycogen content by 47% (143 mmol/kg of wet weight of muscle for the high-carbohydrate diet vs 76 mmol/kg of wet weight of muscle for the high-fat diet), the mean exercise time for the five subjects under investigation did not differ significantly (147 minutes for the high-carbohydrate diet, 151 minutes for the high-fat diet). These results, however, should be interpreted cautiously because one subject rode almost 60% longer after the high-fat diet, skewing the average result.

Probably the longest exposure to a carbohydrate-restricted diet was a recent investigation (26) in which two groups of 10 untrained subjects participated in a 7-week endurance program while consuming a high-fat (62% of energy) or high-carbohydrate (65% of energy) diet. Cycling time to exhaustion at 70% of VO2 max increased by 191% after the high-carbohydrate diet, but only 68% after the high-fat diet. To determine if the performance impairment in the high-fat group could be reversed, subjects switched to a high-carbohydrate diet during the eighth week of the study and repeated the exercise task. Even after a week of ingesting carbohydrate, the mean performance time improved by only 12 minutes, leading researchers to conclude that "a combination of training and a fat-rich diet did not reveal an additive effect on physical performance (26)."

Recently, the idea of "nutritional periodization" for endurance training has been proposed. Athletes might train for most of the year on a high-carbohydrate diet, consume a high-fat diet for 2 to 3 days early in the week before a major event, then carbohydrate-load 48 hours before competition (27). Such periodization would permit endurance athletes to train hard throughout the year and maximize their endogenous carbohydrate stores before competition while, in theory, also optimizing their working muscles' capacity to oxidize fatty acids during a major race. The hypothesis requires scientific testing before any recommendation can be made to athletes.

Even if such a dietary regimen were shown to enhance performance, high-fat diets still increase the risk of a number of diseases (28,29). Though regular physical activity attenuates these risks (28), individuals should limit their long-term exposure to high-fat diets. Short-term use of high-fat diets is associated with insulin resistance in the liver (30), which results in a failure to suppress hepatic glucose output and leads to a reduction in liver glycogen synthesis. For these reasons, caution should be exercised when recommending high-fat diets to athletes.

Individualized Fueling Strategies

Athletes use many nutritional strategies to promote fat oxidation, conserve carbohydrate stores, and improve athletic performance. However, many of these practices, such as the "zone diet (31,32)," have not been rigorously tested.

Even agents shown to have an ergogenic effect when tested under well-controlled conditions may be ergolytic in certain individuals. Negative effects may not be known because there are likely to be many scientific studies that, because they lacked a positive finding, were never published. Accordingly, it is important to recognize that individuals vary in their response to ergogenic substances. Nutrition strategies require the supervision of qualified medical personnel, and should always be fine-tuned during daily training.

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Dr Hawley is associate professor in the department of physiology at the University of Cape Town Medical School and scientific director of the High Performance Laboratory at the Sports Science Institute of South Africa, both in Newlands, South Africa. He is a fellow of the American College of Sports Medicine. Address correspondence to John A. Hawley, PhD, Dept of Physiology, Sports Science Institute of South Africa, Box 115, Newlands, 7725, South Africa.