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CYCLING PERFORMANCE TIPS

  Last updated: 8/16/2010

BASICS OF NUTRITION PHYSIOLOGY
for training and performance


1. The Raw Material - Calories in Food

All physical activity requires energy, and that energy is provided by the food we eat. Although we often view the bakery stop after a ride as just a pleasant reward, smart eating is essential to enjoying our riding and, for those in competitive situations, optimal performance.

All foods are composed of three nutritional building blocks - carbohydrates, fats, and protein - plus water and fiber (indigestible and without any food value). Carbohydrates contain 4.1 Calories per gram and are the primary energy source for most cyclists as well as athletes involved in short, maximum performance events. Fats are more important as an energy source for slower, endurance events. Protein, is used in maintaining and repairing cells, and is rarely an energy source for physical activity except in certain unique situations (such as malnutrition).

How much energy is in the food we eat (or what is a Calorie)?

Some foods contain more energy per ounce (or gram) than others. Not only does the fiber content (a filler with little or no Caloric value) of foods vary, the energy contained in equal weights of the pure basic building blocks - carbohydrate, fat, and protein - is not equivalent. In the nutritional literature, the energy content of any food is, by convention, expressed in Calories (note the capital "C") as opposed to the use of calories (small "c") or kilojoules (kj) in the scientific literature. The energy of one nutritional Calorie is equal to a kilocalorie (1000 calories - lower case "c") or 4.18 kilojoules.

Carbohydrates and protein each contain a little more than 4 Calories of energy per gram while a gram of fat has more than double the energy value at 9 Calories per gram.

2. Converting food Calories to power your muscles

Carbohydrate Calories supply the majority of the energy for muscles during vigorous activity. Fats are important for less strenuous, endurance type activities. Proteins are, in general, not an energy source for muscle activity.

Carbohydrate is provided to the muscle cell from 1) food you are eating or 2) stored carbohydrate in the form of glycogen in muscle and liver cells. On a normal diet, while fasting, there is enough stored glycogen to support 2 hours of high level exercise before these reserves are depleted and the bonk occurs. These internal stores can be extended with oral carbohydrate Calories. Thus, using carbohydrate supplements for events expected to last more than 2 hours is s smart strategy to maximize your performance. It is best to begin these carbohydrates at the start of the event as they are much less effective when one is trying to catch up after the bonk has occurred. A well trained cyclist will need slightly more than 1 gram of carbohydrate per minute to sustain maximum performance, and oral supplementation (started at the beginning of the exercise, not after glycogen depletion has occurred, at that rate) should be contain enough carbohydrate to replace (or protect) these internal glycogen stores .

In addition to extending the time to fatigue in longer, moderate activity events, several studies have also suggested that maximal performance in a 1 hour, high intensity (time trial, ~80% VO2max) event can be improved with oral carbohydrate supplements. In those studies, drinking a liter of a 7% carbohydrate solution at the beginning and during the event improved times by 2%.

Skeletal muscle use carbohydrate that is in the form of glucose - and other sugars must be converted into glucose by the liver before they can be used as fuel by the muscle. Aside from palatability, studies have demonstrated no additional benefit from the use of glucose polymers, fructose, or sucrose (common table sugar, which is a dimer of glucose and fructose) as a carbohydrate replacement. And there can be negative side effects of some carbohydrates, for example, in large amounts fructose can cause diarrhea)

Although carbohydrates are superior to fats for high intensity performance, there is a shift toward fat metabolism at lesser levels of exertion. In fact, the "second wind" that occurs during exercise probably reflects that shift - internal carbohydrate stores have been used, fatigue sets in, the body shifts to fat metabolism, and the "second wind" or feeling of a renewed source of energy returns). However, the trade off is the inability to maintain performance at the prior level that was possible with carbohydrate supported exercise.

Fats provide over 50% of the Calories expended during moderate exercise (less than 50% VO2 max.) even when adequate carbohydrates (glycogen) are available. As the level of exercise increases towards 100% VO2 max., the proportion of the total energy expenditures covered by fat metabolism diminishes. And in maximum performance events, where metabolism becomes anaerobic (greater than 100% VO2 max.), fat metabolism ceases and only carbohydrates are useful to the muscle cell as an energy source. Although there has been speculation that using fats in a dietary program both during training and as supplements during competitive events might improve athletic performance, the only hard evidence to date suggests that it may help endurance (performing at <50%VO2 max) athletes involved in long events while there has been no evidence of a benefit at higher performance levels ie 90 to 100% VO2max.

Protein the third building block of food, is a maintenance material used to repair muscle (and other) cell injuries - including the microtrauma that occurs with exercise. It is NOT used by the body as an energy source except in very malnourished states where fat and carbohydrates are unavailable. Even in endurance activities such as the Tour De France, basic protein needs of 1.5 gms protein/kg body wt/day were easily met by a normal (unsupplemented) diet that replaced the total Calories expended. A review of the literature failed to demonstrate any advantage to protein supplements (assuming an adequate daily protein intake) over pure carbohydrate supplements alone. And one study actually demonstrated a DECREASE in overall performance from the appetite suppressing effects of a high protein diet, subsequent decreased carbohydrate intake, and as a result diminished pre event muscle glycogen stores.

3. Beginning the process - Digestion (more detail)

Before we go any further, let's take a minute to discuss the role of the various parts of your digestive tract.

When designing a nutritional program to supplement the body's energy stores for an athletic event, the rate of digestion and absorption of foods must be taken into account. The time needed for the stomach to start the digestive process, empty its contents into the small intestine, and have the food components absorbed into the bloodstream will directly affect how quickly any food will be available to the muscle to provide the supplemental Calories for exercise.

You have some control over four major factors influencing the digestive process.

From the above four points, it is easy to see that the optimal food for a rapid, high energy boost during a ride would be a semi-liquid or liquid carbohydrate with minimal if any fat. On the other hand, an endurance athlete, competing at a lower VO2 max., might prefer a complex carbohydrate with some fat added to improve taste (and generally in a solid form), in order to slow emptying from the stomach and even out absorption over a longer period of time.

Carbonation does not appear to affect the emptying rate of the stomach. Three independent studies found no difference in the gastric emptying rates of water, carbonated water, and carbonated carbohydrate drinks. Carbonated colas, which contain 160 Calories per 12 ounce can and the caffeine equivalent of half a cup of coffee, remain a favorite drink of many cyclists.

Effects of exercise on the digestive system

Serious athletes often develop gastrointestinal (GI) disorders during training and competition - generally cramps, diarrhea, and nausea (although constipation has been reported). Cramps and diarrhea reflect an over activity of the lower intestinal tract or colon, and are much more common in runners (and thus triathletes) than in cyclists. A recent survey of triathletes participating in a half iron man event revealed that 50 % complained of belching and flatulence (gas), and more symptoms occurred while running than at other times.

Studies have demonstrated a reduced blood flow to the digestive system during vigorous exercise - an 80% reduction after 1 hour cycling at 70% VO2max. And there was a direct relationship in that individuals with the most severe symptoms had the greatest decrease in blood flows. The type of exercise also plays a role, and it is speculated that the mechanical trauma (a jostling effect) to the abdominal organs may explain why runners have more symptoms than cyclists or swimmers. Changes in GI hormone levels have been noted with vigorous exercise, but a cause and effect relationship to symptoms has not been proven. Stress factors are probably more important as a cause of pre competition symptoms such as nausea, vomiting, and diarrhea (which in one study were present in 57% of the participants).

Heartburn (or esophageal reflux)is more frequent when exercising within 2 hours of eating. The current feeling is that this increase in reflux is related to a combination of meal effects (especially fats) on the esophageal sphincter pressure (which prevents reflux of stomach contents into the esophagus), the increased volume of food and acid in the stomach available to reflux, and the mechanical jostling that occurs (especially with running). This is usually a minor problem for cyclists and is best handled by delaying exercise after eating or using an antacid of one of the over the counter acid reducing medications such as Tagamet or Zantac.

Exercise delays stomach emptying, and the more vigorous the exercise, the greater the delay. Running once again appears to have a greater effect than cycling, presumably because of the mechanical jostling of the stomach as well as other abdominal organs. In addition to the increase in esophageal reflux (noted above), the delay in stomach emptying can cause a sensation of fullness and nausea as well as limiting the immediate availability of Calories from the food eaten (as will be discussed shortly). In the survey referred to above, there appeared to be an additive effect from a high fat and protein pre event meal and the use of hypertonic drinks before and during the event. 40% of those drinking a hypertonic beverage had severe complaints compared with only 11% of those who had used isotonic drinks.

An increase in small and large intestinal activity is the cause of abdominal cramps and is reflected in an increase in the frequency of defecation as well. It has been speculated that there might be changes in digestive hormones associated with exercise which then stimulate the colon. But it is more likely that once again the mechanical factor of jostling the bowel is a more important factor. A fiber rich, pre race meal can also play a role. In a recent post race survey, almost all the triathletes who had eaten a high fiber meal suffered from cramps. Minimizing cramps requires a focus on:

Most of these issues are more problematic for runners (and thus triathletes) than cyclists. Except for competitive cyclists, the effects of exercise on the GI tract are minimal.

4. Absorption and metabolic considerations

5. Internal Energy Storage

In the well fed and rested state, it has been estimated that the human body contains approximately 1500 carbohydrate Calories (stored in the form of glycogen) in the liver and muscle tissue, and over 100,000 Calories of energy stored as fat.

The muscles are the main glycogen repository containing anywhere from 300 - 600 grams of glycogen (which equates to 1200 to 2400 Calories) while the liver contains 80 to 110 grams (300 to 400 Calories). The exact numbers are less important than the concept that internal carbohydrate stores are only adequate for several hours of brisk cycling. On the other hand, there is enough stored fat to continue to cycle at a reduced speed (50 - 60% VO2@max) for days.

In order to avoid the "bonk" (depletion of glycogen with a shift to fat metabolism with an accompanying deterioration in performance), supplemental carbohydrates need to be used during the early stages of rides that will be more than longer than 1 to 2 hours in length to supplement (and thus spare) the body's internal glycogen stores.

Muscle fatigue (the "bonk" in cycling, "hitting the wall" in running) generally occurs when the body's internal carbohydrate stores are depleted and the shift towards fat metabolism as the prime energy source for the exercising muscle (with maximum energy output generally limited to approximately 50% VO2 max.)occurs. It would be logical to assume that if adequate carbohydrates (to offset those expended) were replaced during a ride, the cyclist could maintain his or her pace indefinitely. Unfortunately this is not the case. Cyclists with low muscle glycogen stores but high blood glucose levels still experience fatigue at some point, even though the time to onset of fatigue can be delayed by taking the carbohydrate supplements. Unknown factors, perhaps related to physical changes in the muscle cell itself, are thought to be responsible as this type of fatigue is more common in the untrained athlete.(see also Overtraining)

A summary of the important "basics" of nutritional physiology that will help you understand the rationale behind an optimal training and performance diet.

Key elements in developing your own nutritional plan to maximize your training and performance.

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Cycling Performance Tips
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