Chemically, glycogen is a branched glucose polymer, i.e. a type of starch. About 300 g of glycogen is stored in the muscles, though this amount can increase fivefold with physical training coupled with proper nutrition. Muscle glycogen is the primary energy source during exercise. The glycogen store in human liver is about 90 g and is involved in the hormonal control of the blood sugar. Because glycogen is a carbohydrate, it contains water, making it a large and weighty molecule. Such a large molecule is unsustainable for long-term energy storage (as opposed to fat). The 70 Kg "reference man" stores only an 18-hour resting fuel supply as glycogen (or 90 minutes of exercise), compared to a 2 months' supply of fat (or 4 marathons back to back).
Think of glycogen as the "wick" in a candle and our fat stores as the "wax". If we have no glycogen, we cannot sustain a flame and therefore cannot burn energy even with lots of stored fat available. Similar to a candle, our body stores of glycogen (the wick) are very small in comparison to fat stores (the wax), but so very essential (1). In other words, we cannot burn fat without the presence of at least small amounts of glycogen. Therefore, glycogen has to be present for aerobic exercise to continue.
However, glycogen is not only a fuel source for muscles, but also the food source for our brain. Although the muscle can store glucose and burn fat, the brain does neither, but rather feeds on glucose, supplied to it from the blood stream. Since the brain has no fuel storage capacity, it is extremely sensitive to fluctuating glucose levels in the blood. It is well known that depleted blood glucose causes athletes to "hit the wall", or to "bonk" or "crash", as athletes with low blood sugar tend to perform poorly because the under-fueled brain limits muscular function and mental drive (2).
Our body derives energy from 3 main food sources: Carbohydrate, protein and fat. In general, carbohydrates are our main fuel for exercise, though the lower the intensity or longer the duration of exercise, the more we will rely on fat; the predominant role for proteins is to provide the building blocks for muscle and other tissues, but during endurance exercise, up to 15% of energy may come from protein; fats provide a concentrated source of energy and are the second most important contributor to energy demands during exercise, behind carbohydrates.
During exercise, blood glucose levels increase, while blood insulin levels fall. This occurs due to the exercise-induced rise in catabolic hormones (hormones that induce the breaking-down of fuels for energy), which inhibit the release of insulin from the pancreas. In other words, during exercise, the body doesn't need insulin for glucose mobilization, and therefore its' secretion is suppressed. As a result, glucose is released from the liver to the bloodstream, and fat is oxidized for energy. The higher the intensity of your exercise, the more insulin is suppressed.
Endurance training also causes several major adaptations in the muscles to increase fat utilization. First, endurance training increases the number of capillaries in the trained muscles, so that the muscles receive more blood and oxygen. Second, endurance training increases the ability of the muscle to burn fat (activating specific enzymes). Third, endurance training increases tissue insulin sensitivity, which means the muscles need less insulin to allow glucose in, resulting in less insulin in the blood (3). In endurance athletes, the claim that a high carbohydrate diet promotes greater body fat storage through activation of insulin is also, therefore, unfounded.
In conclusion, carbohydrate, and not fat, is the preferred energy source during exercise at or above 70% of VO2max (maximal oxygen consumption) - the intensity at which most endurance athletes train and compete. Fat supplies a secondary source of energy, but becomes more important the longer the duration of exercise. In fact, after several hours of endurance work, fat may supply up to 80% of calories (4). Even at this stage, however, fat still 'burns in a carbohydrate flame'. This means that one must still be mindful of adequate carbohydrate ingestion even at the late stages of a prolonged endurance event when fat usage is maximal.
Significant glycogen depletion occurs during endurance exercise that exceeds 90 minutes (such as marathon running). When glycogen stores drop to critically low levels, high-intensity exercise cannot be maintained. In practical terms, the athlete is exhausted and must either stop exercising or drastically reduce the pace.
However, glycogen depletion may also be a gradual process, occurring over repeated days of heavy training, in which muscle glycogen breakdown exceeds its replacement. The same process may occur during high-intensity exercise that is repeated several times during competition or training. How long does it take to replenish glycogen stores? It depends on the amount of carbohydrates in our diet, and on the timing of their consumption. Generally, it takes 24-48 hours to fully replenish glycogen, which is quite a bit longer than it takes to use it up.
In a classic study (5), glycogen synthesis was compared on a 40% vs. 70% carbohydrate diet during repeated days of 2-hour workouts (Chart 1).
On the low carbohydrate diet: the muscle glycogen stores dropped lower with each successive day of training. After several days of the diet and exercise regimen, the athletes had low muscle glycogen stores, and could not exercise at even a moderate intensity.
On the high carbohydrate diet: the athletes enjoyed nearly maximal repletion of the muscle glycogen stores after the strenuous training, allowing them to continue the heavy training.
This study and others, suggest that athletes who fail to consume enough carbohydrates on a daily basis while training, will likely decrease endurance as well as exercise performance.
Other studies showed dose-related glycogen storage (i.e. a direct relation between the amount of carbohydrates consumed, and the amount of glycogen stored in the muscle). Three diets were consumed by athletes: 15% carbs, 55% carbs and 55-65% carbs. The highest carb-diet yielded 4 times more accumulated glycogen compared to the lowest carb-diet. When these athletes were subjected to "all-out" exercise, their exercise times were proportional to the amount of glycogen stored before the test (Chart 2).
It is suggested that athletes in heavy training should consume a carbohydrate intake of 7 to 10 g/kg bodyweight/day, to help prevent daily glycogen depletion. For example, a person weighing 70kg (154 lb) would need between 490 g a day (70*7), and 700 g a day (70*10), with consideration of total energy needs (Burke LM, 2004).
Remember, carbohydrates are important for not only endurance athletes but also those who train hard day after day and want to maintain high energy. If you eat a low-carbohydrate diet, your muscles will feel chronically fatigued. You will train, but not at your best.
At least 20 hours are required for complete restoration of muscle glycogen, provided approximately 600 g carbohydrate is consumed during that period. However, the timing is as important as the overall amount. The time immediately after exercise is known as the best "window of opportunity" for replenishment. Glycogen synthesis is at its' peak right after exercise (provided an adequate amount of carbohydrates are ingested, around 2 g/kg body weight). Two hours later, muscle glycogen synthesis is cut by a third (to 66% of the building capacity right after exercise), and four hours after exercise it is reduced almost to a half (to 50% of the building capacity right after exercise) (7). This means that delaying carbohydrate intake for too long after exercise will delay muscle glycogen restoration. The current recommendations are to consume 50-100 g carbohydrate within 30 minutes after exercise, to maximize muscle glycogen synthesis (8). Further studies show that multiple consumption over the first two hours (every 30 min.), restores even a greater amount of glycogen in the muscles (9).
Notwithstanding this important research, from a practical standpoint, ingesting this amount of carbohydrate so quickly after exercise, especially after exercise in the heat, may be difficult due to gastrointestinal intolerance. EMEND™ supplies 60 grams of carbohydrate per litre, a great starting point for replenishment of carbohydrates, and an amount that should be tolerated by most. If you can tolerate more than this based on the condition of your gastrointestinal tract, then you may supplement with other carbohydrate sources.
Not only does consuming carbohydrates immediately after exercise help restore muscle glycogen stores faster, but adding about 5 to 9 g of protein with every 100 g of carbohydrate will further increase the glycogen synthesis rate (9, 10). Extra protein on top of this will likely not alter the rate of glycogen restoration, though it will provide valuable protein for muscle repair as a part of overall adequate dietary protein intake.
Again, notwithstanding the research quoted above regarding carbohydrate replacement, from a practical standpoint, ingesting this amount of carbohydrate so quickly after exercise, especially after exercise in the heat, may be difficult due to gastrointestinal intolerance. EMEND™ supplies 60 grams of carbohydrate per litre, a great starting point for replenishment of carbohydrates, and an amount that should be tolerated by most. If you can tolerate more than this based on the condition of your gastrointestinal tract, then you may supplement with other carbohydrate sources.
It is well known that the higher the glycemic index of the carbohydrates in your post exercise diet, the quicker and the more efficient will be the process of glycogen restoration. The principle carbohydrate in EMEND™ is dextrose, having a glycemic index of 100, which tops out the glycemic index scale. A high glycemic index helps ensure rapid absoprtion and utilization of the carbohydrate. One of the reasons this happens is because at rest (recovery), a high glycemic index carbohydrate stimulates insulin secretion, which is exactly what you want to happen in order to augment glycogen restoration. Dextrose does this quite well. Dextrose is also known for it's postitive effect on sodium absorption, which is absolutely necessary for enhanced recovery.
Dextrose, therefore, was selected as EMEND™'s primary carbohydrate for several important reasons:
Furthermore, a sports recovery drink must be sweetened to enhance its' taste. Currently, there are several ways to sweeten a drink:
These include Nutrasweet™ (Aspartame), Splenda™ (Sucralose) and Sweet One™/Sunette™ (Acesulfame K). At EMEND™, we don't like artificial sweeteners, for several reasons:
While there are many natural sweeteners, most commonly used in sports drinks are fructose (fruit sugar) and sucrose (cane/table sugar). Fructose has a low glycemic index (GI = 24), is known to irritate the gastrointestinal tract, making it a bad choice for a product designed to help athletes recover from exhausting exercise. These negative effects increase in direct proportion to the fructose concentration in the product .
Sucrose is the logical choice for EMEND™. It is natural, provides a good source of carbohydrate energy (sucrose has a Glycemic Index of 64), and does not produce gastrointestinal tract irritation. It is easily absorbed and pleasantly sweet, improving palatability. Some people are concerned about sucrose, and some companies take advantage of this concern by continuing to perpetuate the myth that a little table sugar is somehow going to lead us to our destruction! In truth, no one single carbohydrate should be the principle carbohydrate in our diets, and for some people, sucrose is the principal carbohydrate ingested on a daily basis. The medical staff at EMEND™ agree that this is not ideal for optimum health. However, some sucrose in our diets is perfectly fine and safe, and as a palatable, non-nauseating natural sugar that offers rapid absorption and fueling, sucrose works very well, and by far is the best choice for sweetening sports nutrition products.
A final note is the stevia plant, which produces a natural, no calorie sweetener that is being used more and more in various foods/products on the market. Our problem is this: if it doesn't have any calories, it is of no use either during or after exercise i.e. it is analogous to any of the other non-caloric sweeteners like aspartame, sucralose or acesulfame K in this regard. We not only rely on our sweeteners to sweeten, but also to provide an easily absorbed carbohydrate source to help replenish our glycogen stores - stevia, while pleasantly sweet, does nothing to replenish our glycogen stores, so is of minimal use in a sports recovery product. Save this one for diet products!
Protein is a group of nitrogen-containing compounds formed by amino acids (the building blocks of protein). Protein serves numerous functions in our bodies:
Proteins are constructed from a variety of essential and non-essential amino acids.
All sports involve the breakdown of muscle tissue, or catabolism. In trying to make athletic gains, you intensify the process. Instead of doing the same workout every day, which keeps you at the same level of fitness, you add repetitions or distance to increase your endurance, or weight to increase your strength. Sometimes, in an attempt to step up to a higher performance level, you really challenge your body. To varying degrees, the result is muscle breakdown, possibly even with micro-injuries to the muscle tissue, and the notorious DOMS (11). DOMS, or delayed onset of muscle soreness, usually occurs a day or two after intense training.
Because certain amino acids are the building blocks of protein, they are major key players in fighting muscle wasting, repairing muscle tissue, and advancing muscle recovery and development. In short, the answers to "why protein?" are (12)
The amount of protein needed is one of the oldest arguments in sports nutrition. Although it has long been a popular belief among athletes that additional protein increases strength and enhances performance, sports dietitians and physiologists generally hold that data are not available to support this thesis. Basically, the small amount of protein required for muscle development, is easily met by the average diet, which contains 12-15% protein, or an amount of 1.2-1.4 g of complete protein per kg body weight per day for the endurance athlete, and 1.6-1.7 g of complete protein per kg body weight per day for the strength athlete. The reference 70 Kg (154 lb) endurance athlete will need about 84 to 98g, and the strength athlete about 112 to 119 g of protein a day (13). However, these amounts of protein depend on two main factors:
In conclusion, the right amount of daily protein is either 12-15% of daily calories, or 1.2-1.4 g/kg/day for endurance and 1.6-1.7 g/kg/day for strength athletes. These guidelines are predicated on the assumption that complete proteins are being ingested and that the diet is calorically sufficient.
As in carbohydrates, protein synthesis and tissue recovery is at its' best right after training, and no later than 30 minutes from the moment you climb off of your bike, step off the track or drop your weights. But replenishment doesn't stop there. As in the case of glycogen, muscle recovery and protein need is a 48 hour process, therefore whole meals with a mixture of proteins and carbohydrates should be consumed, if possible, every 2-3 hours over this period. Vegetarian based proteins, like soy, while generally healthy, are not complete proteins, and therefore their biological value is not as high as animal based proteins. So, use of vegetable based proteins requires combining various vegetable sources to achieve the full complement of essential amino acids required for health. If you are a strict vegetarian, therefore, you must ensure that these concepts are taken into account to maximize your recovery.
In the first 30 minutes, you should aim for at least 5-10 grams, in combination with carbohydrates. The best protein to use is high biological value protein with fast absorption, such as high quality whey protein. We have taken this aspect of our drink very seriously, and have sourced one of the best prepared and highest quality sources of whey protein in the world. Each litre of EMEND™ supplies 15 grams of ultra filtered whey protein per litre in a ratio with carbohydrates that, above all, enhances fluid and electrolyte absorption, carbohyrate and protein repletion and maximizes taste.
As demonstrated in Chart 3, at rest, most water loss is due to losses from skin and respiration, which is also known as "insensible water" (a loss we cannot normally sense), and urine losses. During prolonged exercise, on the other hand, the most profound water loss is through sweat.
Seldom is water thought of as a nutrient because it has no caloric value. Yet its' importance in maintaining life is second only to oxygen. Water constitutes about 60% of a young male's (or 50% of a young female's) total body weight. It has been calculated that we can survive losses of up to 40% of our body weight in fat, carbohydrate and protein. But a water loss of 9% to 12% of body weight can be fatal.
As exercise intensity increases, so does the metabolic rate. This increases body heat production, which, in turn, increases sweating. Thus, during exercise, water loss is accelerated. As your body's temperature rises, sweating increases in an effort to prevent overheating (link to heat related illnesses in e load). During an hour of intense training, for example, a 70 kg person might lose as much as 1500 ml (1½ Liters), although under extreme exercise and environmental heat stress, water loss can be as much as 2 to 3 L per hour.
Even minimal changes in your body's water content can impair endurance performance. Without adequate fluid replacement, a subject's exercise tolerance will show a pronounced decrease during long-term activity because of water loss through sweating (chart 4). Distance runners, for instance, are forced to slow their pace by about 2% for each percent of body weight loss by dehydration.
When you feel thirsty, you drink. The thirst sensation is regulated in your brain. It triggers thirst when the concentration of the electrolytes in your blood is increased. Unfortunately, your body's thirst mechanism is a mechanism out of tune. You don't sense thirst until well after dehydration begins. Even when you are dehydrated, you might desire fluids only at intermittent intervals, and crave smaller amounts than needed.
Those who sweat heavily and lose considerable amounts of fluid may require 24 to 48 hours to completely replace lost water if they drink when guided by thirst alone. Because of our sluggish drive to replace body water, and in order to prevent chronic dehydration, we are advised to drink more fluid than our thirst indicates.
Because of the increased water loss during exercise, it is imperative that athletes' water intakes are sufficient to meet their bodies' needs, and it is essential that they rehydrate during and after each exercise bout.
First of all, do your best to minimize fluid loss during the exercise itself. (See the e load™ Fluid Calculator)
After exercise, the best way to know how much fluid you need is to weigh yourself just before, and right after your training or event. The weight difference is usually due predominantly to fluid loss. To replenish fluids lost during exercise you need to drink 750 ml of fluid for every 500 ml lost (about 3 cups for every pound) (14, 15). It was once thought that fluid replacement should be equivalent to fluid loss (kilogram for kilogram/pound for pound). However, more recent research indicates that 1 ½ x the loss is needed to completely replenish (16). That means that even a modest loss of 1 kg of water not replaced during exercise will require the ingestion of 1½ Litres of liquid after exercise to rehydrate. In order to optimize this process, it is imperative that your fluid contains at least 900 mg of sodium per litre (see Electrolytes).
See our Post Exercise Fluid Calculator to determine the best way to recover your fluid losses
Since full rehydration might take up to 48 hours, an athlete who trains on a daily basis could become chronically dehydrated, predisposing him/herself to chronic underachieving. Efficient rehydration is also imperative for athletes who engage in multiple events on the same day. Rapid recovery of fuel sources and fluids will enable optimal performance.
The electrolyte concentration in sweat varies with:
In addition to losses through sweat, electrolytes are lost through urine production and excretion. Aside from clearing wastes from the blood and regulating water levels, the kidneys also regulate the body's electrolyte content and concentrations. At rest, electrolytes are excreted in the urine as necessary to maintain homeostatic levels (i.e. keeping a steady concentration of substances in the blood). As your body water loss increases during exercise, your urine production decreases considerably in an effort to conserve water. Consequently, with very little urine being produced, electrolyte loss via this route is minimized.
The replacement of electrolytes, particularly sodium and potassium, is essential for effective rehydration. If sufficient amounts of water, sodium and postassium are ingested, plasma volume is more rapidly restored to normal, thus preparing you for your next exercise session.
Many studies have found that rehydration with water alone dilutes the blood rapidly, increases its volume and stimulates urine output. Blood dilution lowers the thirst drive, thus undermines adequate fluid replacement. Therefore, rehydration with an electrolyte-enriched solution is the beverage of choice (17, 18, 19, 20, 21, 22, 23, 24, 25).
A high quality recovery drink should therefore contain:
Free radicals are molecules, or fragments of molecules, that are extremely unstable, potentially disrupting normal metabolism. Because of this molecular instability, free radicals are highly reactive and can promote damaging oxidation reactions with proteins, lipids or DNA, leading to impaired cellular function. Small amounts of radicals are normally created in our body during normal aerobic metabolism. They are converted by anti-oxidants to benign, harmless compounds. Antioxidants, which protect our body from free radical damage, include a wide variety of substances such as vitamins C, E, A, Carotenoids, Bioflavonoids, Ubiquinones, Zinc, Selenium, etc.
Although regular physical exercise has many beneficial effects, it is now clear that muscular exercise results in increased production of free radicals and other reactive oxygen chemicals in the working muscle. Growing evidence indicates that reactive oxygen chemicals are responsible for exercise-induced protein oxidation that contributes to muscle fatigue (26). To protect against this oxidative injury, muscle cells contain complex defense mechanisms, some of which involve these dietary antioxidants.
In addition to oxidative damage, acute, prolonged exercise results in temporary alterations in inflammatory functions, which appear to imitate the body's response to infection. That is to say, our body reacts to a prolonged, strenuous exercise as it would react to infection (27, 28). Acute and intensive bouts of prolonged physical exertion, such as at that experienced by athletes participating in ultramarathon events, have also been reported to result in an increased susceptibility to respiratory post-race infections. Such vulnerability is caused by a temporary "open-window" period that persists for 6-20 hours immediately post-race, during which the immune system is suppressed. Intake of antioxidants, and specifically vitamin C, has been shown in some studies to decrease the incidence of post-race respiratory infection (29).
In conclusion, athletes need antioxidants mainly to protect the muscle against oxidative injury, and to boost the immune system.
As a result of exercise, the oxidative process in the muscle increases, leading to increased generation of lipid peroxides (damaging lipids within the muscle) and free radicals, sometimes up to threefold. Vitamins with antioxidant activity, particularly vitamin C, vitamin E and ß-carotene, neutralize free radicals and possibly enhance recovery from exercise. However, it is generally advised to supplement prudently with antioxidants, since in excessive amounts an antioxidant has a tendency to act as an oxidant. In addition, some of the antioxidants are fat-soluble compounds (such as vitamin A and E), therefore hard to dispose of when in excess, unlike water-soluble antioxidants (such as vitamin C) that can be excreted in the urine. For this reason, EMEND™ has been formulated with vitamin C, which is a great antioxidant, but in case you may already be ingesting enough from other sources (i.e. diet, supplements), any excess Vitamin C will be excreted in your urine.
For EMEND™, we have chosen a special form of Vitamin C called Calcium Ester C, which is a buffered (low acid) form of Vitamin C compared to coventional preparations. This helps control the overall acidity of the drink, making it much more stomach friendly.
Recommendations are ingesting up to 1000 mg/day of Vitamin C (3), though some research shows that any amount over 600mg/day is excreted in the urine.
One of the reasons why a sports drink can be irritating to your gastrointestinal tract is its' acidity level. The standard measure of acidity is pH, and this number refers to the concentration of H+ or protons in the solution. The pH scale is an inverse scale ranging from 0 - 14, with numbers less than 7.0 being acidic, having more H+ than OH-, and vice versa for basic (alkaline) solutions with pH values above 7.0. The pH of distilled water is 7.0, having equal numbers of H+ and OH-, making it neutral. The ideal pH for any beverage is therefore 7.0.
Because the pH scale is logarithmic, a one unit change in pH is associated with a 10 fold change in the concentration of H+. For example, lemon juice has a pH of 2.0, while grapefruit juice has a pH of 3.0. Lemon juice would therefore be 10x the acidity of grapefruit juice. As another example, coffee has a pH of 5.0. Lemon juice would have 1000x the acidity of coffee (10 x 10 x 10) (see Chart 5).
Some ingredients used in sports drinks add acidity to the drink, including flavors and citric acid. Citric acid is a natural compound that helps control "tartness", and really does improve the palatability of most prepared drinks. Other ingredients add base to the drink, like protein powder. Fortunately, EMEND™ has a relatively neutral pH and this is a big reason why EMEND™ is very well tolerated by most who use it, especially after a workout in the heat. In fact, EMEND™ has 4 times less acidity than Endurox , and 17 times less acidity than Powerbar Recovery (See Product Comparison Chart). Prolonged exercise, especially in the heat, is especially stressful, and as such will increase the amount of acid in your stomach (stress increases stomach acid, as many of you with stomach ulcers will know). This can lead to stomach pain/cramps. Therefore, you want to minimize the amount of acid in your drink. A pH of 7.0 is neutral, like water; a pH above 7.0 is basic, and a pH below 7.0 is acidic. Since protein is basic (the opposite of acidic), drinks that contain a relatively high amount of this compound are more likely to have a higher pH, often above 7.0. These very high protein drinks are more difficult to digest, especially after intense exercise in the heat. Drinks with a pH below 7.0 are likely to have a more stomach friendly amount of protein, and the closer to 7.0 their pH, the more stomach friendly the drink. EMEND™ has a pH of almost 5.0. This is the closest to 7.0 of any recovery drink with a pH less than 7.0, indicating a level of protein and overall acidity that is stomach friendly.
Dear Dr. Stoddard:
As defending Rowing World Champions, my teammates and I are training hard to win again this summer in the 2008 Beijing Olympics. Training more than thirty hours per week means that fluid intake and electrolyte replacement is key to maintaining our intensity on the water. E load has been a big part of our winter training, and will be a real asset when we go into the heat of the Beijing Olympics this summer.
Kyle Hamilton 2002, 2003, 2007 Rowing World Champion, Men's Eight, 2008 Olympic Men's Eight Gold Medallists.
Congratulations to the Canadian Men's 8 Rowing 2008 Olympic Gold Champions fueled by e load!
Derek Zanstra - Mountain Bike
Ingrid Cluzeau - Duathlon
Krista Duchene: National Marathon Champion