Eat To Compete

Eat To Compete
March 2006Darren McWilliams BSc(Hon)
BASES Sport & Exercise Scientist

This leaflet provides nutritional advice to enhance your ability for success in endurance cycling. There is a wide and varied range of topics in this discipline of sports science, therefore I will only concentrate on a few of these areas that should be most beneficial to your cycling performance.

The topics I will cover are:
– Carbohydrate eating strategies prior to training and competition
– Carbohydrate feeding during exercise
– Feeding strategies to enhance recovery
– Fluid replacement requirements during exercise and recovery

It is important to note that these guidelines are beneficial to those cyclists who regularly compete and those involved in touring events such as the Tour of the Glens and Wicklow 200.

Why are nutritional strategies so important?
Research has shown that endurance performance will be maintained if athletes replace lost fluid and carbohydrate during exercise. The importance of replacing carbohydrate and / or fluid will depend on the conditions in which exercise is conducted.

Maughan et al (1996) suggested fluid and carbohydrate intake will be dependent on the following conditions:
– intensity of exercise
– duration of exercise
– ambient temperature
– relative humidity.

As the intensity of exercise increases the athlete’s body will shift from oxidising (burning) a combination of carbohydrate and fat to oxidising a larger amount of carbohydrate. At high intensities the athlete’s body will only rely on carbohydrate as the source of fuel for energy production. At these high intensities of exercise the body’s stores of carbohydrate may become depleted in as little as 45-60 minutes. Exercise at this intensity could include chasing down a break in a road race, conducting interval training or trying to stay with a large group of riders during a touring event.

Our bodies will only store a limit amount of carbohydrate, therefore if this carbohydrate is not replaced during high intensity exercise then the body will suffer from the condition know in cycling circles as getting the knock or the bonk. The technical term for this is hypoglycaemia, which simply means a reduction in plasma glucose concentrations.

It is not only during high intensity exercise that athletes can suffer from hypoglycaemia. During exercise at moderate intensities, similar to those ridden during winter training rides or touring events, athletes became hypoglycaemic after 170 – 180 minutes.
Coyle et al (1996), Coggan and Coyle (1997)

When hypoglycaemia occurs the intensity of exercise the athlete can sustain becomes greatly reduced. Ask anyone who has run a marathon. There are various strategies that can be used to offset fatigue from hypoglycaemia, including topping up the body’s carbohydrate stores before exercise, maintaining carbohydrate feeding during exercise and replacing lost carbohydrate after cessation of exercise.

Before we look at these strategies it is important to consider other ways in which the body will become fatigued. From a nutritional perspective the other major risk factor that will reduce endurance performance is dehydration and the associated hyperthermia.

Many research papers have published the detrimental effects on endurance performance from dehydration and hyperthermia. I will not list all of these papers here, but simply report the findings of a couple of these papers.

Of primary importance here are the findings from Ed Coyle and Ron Maughan’s work on dehydration and hyperthermia effects on endurance performance. A loss of as little as 1300ml of body water through sweating can result in an increase in heart rate by 8 beats per minute, a decrease in cardiac output by 1 litre per minute and an increase in core body temperature by 0.3OC.

The effects of these changes in cardiovascular functioning are three-fold.
1. Anyone who becomes dehydrated while training with a heart rate monitor may not be training effectively in the correct training zone as the heart rate will be unnaturally elevated as a function of dehydration and not an elevation in training intensity.
2. As the majority of fluid loss is from plasma, the blood becomes thicker, the heart has to work harder to pump blood around the body and the amount of oxygen that the heart can deliver to working muscles becomes reduced.
3. The elevation in core body temperature causes an increase in the perception of effort at any intensity of exercise. This elevation in core body temperature also causes an increase in sweat rate thereby compounding the problem of dehydration.

As with carbohydrate feeding, fluid replacement strategies employed correctly before, during and after exercise will reduce the risk of fatigue thereby maintaining endurance performance.

Carbohydrate feeding in preparation for endurance exercise
Compared to body fat stores, the body will only store a small amount of carbohydrate (see Table 1).

Table 1. Typical macronutrient content for a 70kg male.
Glycogen (kcal) Fat (kcal)
Liver 400 450
Skeletal muscle 1200 350
Adipose tissue 0 135,000
Total 1600 135,800
Source: Cahill (1976)

During endurance performance carbohydrate (CHO) is utilised as a major source of fuel for energy production. High intensity efforts such as chasing down breaks, attacking on climbs or sprinting at the end of a race require CHO as it is the only source of fuel utilised by the body. Therefore it is important that muscle CHO stores are maintained during performance. This can be achieved by loading muscle CHO stores before performance, eating to maintain CHO stores during performance and for multi-stage events or consecutive days of training, replenishing CHO stores after each stage.

The traditional glycogen loading technique was popularised in running magazines during the 70’s and although many athletes still use this technique successfully, it does have it’s side effects. These side effects occur following the muscle glycogen depletion ride and during the following depletion phase when the amount of carbohydrate in the diet is reduced (generally days 4 to 6 before the event). The effects are experienced by feelings of irritability, fatigue, reduced tolerance to stressful situations, and the list goes on. Call me fussy but these are feelings I would not like to experience 3 or 4 days before a major event such as the an important road race or the Wicklow 200.

A more recent technique suggested by research to boost muscle glycogen stores is easier to administer, and does not include the side effects associated with the muscle glycogen depletion phase. The current technique is to simply eat large amounts of carbohydrate in the two hours post-competition or training, as it is during these two hours that resynthesis of glycogen within the muscle is greatest, (Ivy et. al., 1988). This has been shown to significantly increase muscle glycogen stores above those of pre-exercise levels.

When I say large amounts of carbohydrate after exercise or training, this is approximately 30g of carbohydrate every 15min for the two to four hours post-exercise. A piece of fruit, bowl of cereal, a sandwich is adequate to provide 30g of CHO. It is also advisable to eat a small quantity of protein during this period as this may aid muscle glycogen resynthesis. In fact the first feed immediately after the event should include a source of the amino acid leucine. This ensures adequate recovery of muscle glycogen stores, and speeds up the recovery of damaged tissue after the event. A serving of approximately 30g of protein is sufficient in the first feed after training or competition. In my own experience I find Science In Sport Rego recovery drink the best on the market for this purpose. There are alternatives to this product. Some people tend to use an amino acid drink along with other foods that contain a carbohydrate source. However it is important if you compete that you are sure of the origin of any nutritional product that you use to ensure it contains no banned substances.

These feeding techniques should be attempted in training first, and NOT on the day preceding or during competition or the event.

Carbohydrate feeding during performance
For events exceeding 1 to 1.5hours it is important that you feed to maintain muscle glycogen stores. These stores usually become depleted after 1.5hours of moderate to high intensity exercise.

The source of CHO ingested is down to individual preference. This could be in the form of energy drinks, energy bars, pieces of fruit, cakes bars, etc. Remember the most important factor is the palatability of your chosen food source. There is no point choosing a food source that gives you gastric problems during competition or the event. Again it is important to try this out in training before trying it in competition.

The primary purpose of carbohydrate ingestion during strenuous exercise lasting longer than one hour is to maintain a sufficient concentration of blood glucose and to

sustain a high rate of energy production from blood glucose and glycogen stored in muscles (Coggan & Coyle, 1991; Coyle et al., 1986), which can allow competitors to exercise longer and sprint faster at the end of exercise (Coggan & Coyle, 1991). Most studies demonstrating improved performance with carbohydrate feedings have given subjects 25-60 g of carbohydrate during each hour of exercise (Coggan & Coyle, 1991; Murray et al., 1991). It is therefore recommended that individuals consume 30-60 g of carbohydrate per hour (Coggan & Coyle, 1991).

If you are taking a sports drink during exercise this could provide approximately 30g of carbohydrate for every 500ml of sports drink. For those involved in a road race feeding with solid food may not be practical. In this situation 500ml of a sports drink and an Energy Gel would provide the required carbohydrate to sustain the intensity of exercise to the finish line.

Fluid replacement for endurance performance
The extent to which even a slight degree of dehydration adversely affects bodily function during exercise and the situations in which adding carbohydrate and sodium to water provides added benefit is not generally appreciated. The volume of fluid that most athletes choose to drink voluntarily during exercise replaces less than one-half of their body fluid losses (Noakes, 1993).

A large percentage of general population suffer from long-term dehydration. There is no reason to believe this is any different for the majority of endurance athletes. From personal experience I have found cyclists tend to drink very little while training or riding touring events.

Recommended intakes of fluid for optimum health are 30-35ml of fluid per kg body mass per day. For an average endurance athlete this amounts to 2.1 to 2.4 litres of fluid per day. This does not take into account the fluid requirements during exercise.

The American College of Sports Medicine (1996) suggest ingesting 600ml of fluid 2 hours prior to endurance exercise. This permits the athlete’s body to absorb and regulate total body water and to start exercise in a state of euhydration.

The decision as to how much fluid to ingest during exercise should be based upon a risk-benefit analysis. Undoubtedly, the most serious consequence of inadequate fluid replacement, i.e., dehydration, during exercise is hyperthermia, which when severe will cause heat exhaustion, heat stroke, and even death. The risks of too much fluid ingestion are gastrointestinal discomfort (Rehrer et al., 1990) and a reduced pace during competition associated with the physical difficulty of drinking large volumes of fluid while exercising. The benefits of fluid ingestion are reduced cardiovascular stress and reduced hyperthermia that, by themselves, can probably improve exercise performance.

The preferred method of calculating fluid intake requirements is to measure nude body mass before and after exercise. Every loss of 1 kg of body mass equates to a loss of approximately 1L of fluid. Therefore future fluid intake strategies during exercise can be adjusted to accommodate the difference.

Most sports drinks contain carbohydrates and electrolytes in solution. It was previously thought that the addition of carbohydrate to solutions impaired fluid replacement because carbohydrate is known to slow the rate at which fluids empty from the stomach (gastric emptying). However, the most important factor regulating gastric emptying and fluid replacement is the volume of fluid ingested; the carbohydrate concentration of the solution is of secondary importance (Coyle & Montain, 1992a; Coyle & Montain, 1992b, Mitchell et al., 1989; Noakes et al. 1991b; Rehrer et al. 1990).

Practically speaking, solutions containing up to 8% carbohydrate appear to have little deleterious influence on the rate of gastric emptying, especially when the drinking schedule adopted maintains a high gastric volume (Coyle & Montain, 1992b; Houmard et al., 1991; Mitchell et al., 1988; Noakes et al., 1991b). To work out the carbohydrate concentration in your drinks look at the amount of carbohydrate available when the drink is made up, this is usually given on the side of the pack. There should be approximately 6-8g of carbohydrate per 100mL of fluid.

Thus, it is quite possible to ingest 36-100 g of carbohydrate per hour and still replace 600-1,250 ml of fluid per hour. You should have no difficulty drinking 600 ml/h of a 6% carbohydrate solution. Sodium levels of 10mmol.L-1 of fluid or around 400mg.L-1 are recommended to increase rate of water uptake across membrane of the small intestine. The advantage of ingesting drinks with electrolytes such as sodium and potassium is that these electrolytes permit the retention of ingested fluids.

If sodium is not replaced in the fluid ingested dilute plasma is produced thereby stimulating dilute urine production. Therefore the body will not retain all the ingested fluid and the athlete may still be in a state of dehydration even after ingestion of large quantities of plain water. Ingestion of solid food with plain water does not have the same effect, as any solid food ingested will contain electrolytes thereby stimulating fluid retention in the body.

Products such as Science In Sport Go Electrolyte or Isostar adequately meet these demands for fluid replacement and also provide an important source of carbohydrate.

1. During prolonged exercise in the heat, people can become dehydrated at a rate of 1-2L every hour (about 2-4lbs or 1-2kg body weight loss per hour). The rate of dehydration can be monitored by recording changes in nude body weight. Each kilogram of weight loss corresponds to 1L of dehydration.

2. Even a slight amount of dehydration causes physiological consequences. For example, every litre of water lost will cause heart rate to be elevated by about eight beats per minute, cardiac output to decline by 1 L/min, and core temperature to rise by 0.3o C when an individual participates in prolonged exercise in the heat.

3. When it is important to minimize disturbances in cardiovascular function and body temperature and to reduce the perceived difficulty of exercise, people should attempt to drink fluids at close to the same rate that they are losing body water by sweating.

4. Unfortunately, cyclists generally drink only 300-500ml of fluids per hour and thus allow themselves to become dehydrated at rates of 500-1,000ml/h. Dehydration compromises cardiovascular function and places the cyclist at risk for heat-related injury.

5. Start exercise euhydrated by consuming 600ml 2 hours before.

6. For an exerciser who weighs about 68 kg (150 lb), the requirements for both carbohydrate (i.e., 30-60 g/h) and fluid during prolonged exertion can be met by drinking 625-1,250 mL/h of beverages containing 4-8% carbohydrate. This volume must be adjusted for persons of different body weights. For example, an individual who weighs 50 kg should multiply the above recommendation by 50/68 or 0.74, i.e., 462.5-925ml/h.

7. Sodium levels of 10mmol.L-1 of fluid or up to 400mg per litre are recommended to increase rate of water uptake across membrane of the small intestine and retain water in the body.

8. At certain times of the year it may be more important to place emphasis on either CHO feeding or fluid replacement depending upon the ambient conditions.

9. Start exercise sessions with muscle glycogen stores full by eating 30g of carbohydrate every 15 minutes for 2 hours after cessation of endurance exercise.

10. All the nutritional strategies should be practised in training before implementing them in competition.

Any queries should be directed to me at:

Darren McWilliams BSc(Hon)
BASES Sport and Exercise Scientist
07786 322416