Fueling Prior to Training or Competition

Carbohydrates: Fueling for Performance

  

Eating prior to training or games serves the primary purpose of maximizing energy stores for activity, with glycogen being of main concern. This should be of a concern not only in the hours before training, but also in the several days prior. Studies of glycogen synthesis have shown that stores can be normalized by 24 hours of rest and adequate consumption of carbohydrates. Intakes between 7 and 10g/kg bodyweight per day of carbohydrates are sufficient to maximize glycogen saturation. This would correlate to a 100-kg (220 lb) football player consuming 700 to 1000g of carbohydrates in the 24 hours prior to competition. The needs of the athlete…. may be slightly lower than the given values, as an athlete with a larger percentage of body fat, and a lower percentage of metabolically active tissue, will require less carbohydrates than these values show. The stores created by this range are adequate for the muscle fuel needs of events lasting less than 60 to 90 minutes in duration. Values above this, such as with carbohydrate loading, do not enhance performance in events of this duration.

Research examining the effects of carbohydrate consumption on maximal power and resistance training has also shown correlations with glycogen stores. Strength and power are not only products of the exercise stimulus, but also to the stimulus created through nutrition, particularly with recovery. If optimal intakes do not occur between training sessions, recovery, and as a result, performance in the subsequent training series will be negatively affected.

The typical resting values for muscle glycogen in trained muscle are 100-120 mmol/kg net weight. A typical glycogen synthesis rate is ~5 mmol/kg/hour and therefore 24-36 hours should be set aside following the last training session in order to allow for maximal glycogen re-synthesis. An example of this would be to either eliminate exhaustive practices in the 1 to 2 days prior to competition, or to taper training to only movements that do not significantly elevate an athlete’s heart rate.

Consuming carbohydrates prior to training or games should also be a factor in the hours prior to the event. A significant factor involved with whether the athlete chooses to consume a meal prior to sports participation is comfort. Many athletes are not accustomed to eating or taking supplements prior to heavy exercise and the meal could cause gastro-intestinal or psychological discomfort. The goals of the pre-event meal are to:

1) Continue to fuel muscle glycogen stores if they have not fully restored since the last training session

2) Restore liver glycogen content, particularly for events in the morning where liver stores are depleted from an overnight fast

3) Ensure the athlete is well hydrated

4) Prevent hunger, but avoid gastrointestinal discomfort during training

Through research of glucose metabolism and exercise performance it has been determined that the optimal range of carbohydrate intakes in the hour prior to training should be between .6 and 1.0 g/kg bodyweight. Liquid carbohydrate supplements are sometimes preferred over solid foods, due to their decreased gastrointestinal transit time (time in the GI tract) and increased absorption.

Fueling During Training or Competition

The purposes consuming carbohydrates during training is to maintain elevated blood glucose and preserve muscle and liver glycogen. If blood glucose levels begin to fall, glycogen reserves will be used to maintain these levels to sustain the high work rates. When hypoglycemia occurs, glycogen reserves become utilized to a greater extent and can become diminished. Work rates must then decrease to a point in which beta-oxidation, or the metabolism of fats for fuel, can produce the ATP needed. During sports, it is important to maintain blood glucose levels above 2.5 mmol/L. Below this level, physiological and psychological consequences may occur that impede athletic performance. Several of the common symptoms include dizziness, disorientation, and nausea, and most importantly fatigue.

The type of carbohydrate most preferred is in the liquid or in semi-liquid form, either as sports drinks or carbohydrate gels. A list of commonly used supplements is displayed in the previous section. Many studies have looked at the rates of carbohydrate oxidation during intense exercise, as this will help determine optimal timing of intakes and volumes. In general, during short-term intense exercise, such as during football, it is recommended that athletes consume 6-8 oz of 5-7% glucose solution or electrolyte drinks. This equates to approximately 20g of carbohydrates every 15 minutes, or 1 to 2 small cups of a sports drink during rest periods on the sidelines⁸. Caution must be taken because although carbohydrate intakes may be sufficient, an athlete’s fluid needs may not be adequate. Fluid intakes are recommended of 1.5-2.0 mL/kg bodyweight every 20 minutes. An example would be a 100 kg (220 lbs) athlete needing 150-200 mL of water every 15 to 20 minutes. In addition to carbohydrate replacement drinks, water should be ingested at regular intervals to prevent the onset of thirst or hypo-hydration.

Fueling After Training or Competition

The immediate replenishment of fuel reserves after training is strongly correlated with an athlete’s abilities to adapt to the stresses of training. If recovery is sub-optimal, these adaptations will be hindered, and the increased development of strength or power capabilities will be affected. A significant amount of research looking at recovery from exhaustive, repetitive exercise has formulated several guidelines with regards to fuel replenishment. They are listed below.

1) Initiate carbohydrate feeding immediately (within 1 hour) after exhaustive exercise

2) Consume high glycemic carbohydrates (0.7g glucose or sucrose/kg bodyweight or 50g carbohydrate) every 2 hours for the first 4-6 hours. Manipulation is required during pre-season training with multiple practices

3) After 6 hours, low glycemic carbohydrates should be consumed totaling approximately 500-700g, or ~7g/kg bodyweight⁹.

In conclusion, the importance of carbohydrates can be found in most studies to be paramount before, during, and after workouts. The pre-workout optimal range of carbohydrate intakes in the hour prior to training should be between .6 and 1.0g/kg bodyweight and in the form of liquid or semi-liquid form to ensure the athlete will maintain hydration and increase the glycogen stored and used for exercise. Equally as important is utilizing carbohydrates right after exercise in the form of high glycemic carbohydrates (0.7g glucose or sucrose/kg bodyweight or 50g carbohydrate) every 2 hours for the first 4-6 hours to replenish glycogen stores and help with recovery.

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Evolution Nutrition

References

1. Friedman JE, Neufer PD, Dohm GL. Regulation of glycogen resynthesis following exercise. Dietary considerations. Sports Medicine. 1991;12:313.
2. Febbraio MA, Keenan J, Angus DJ, Campbell SE, Garnham AP. Preexercise carbohydrate ingestion, glucose kinetics, and muscle glycogen use. Journal of Applied Physiology. 2000;89:1845-51.
3. Haff G, Lehmkuhl MJ, McCoy LB, Stone MH. Carbohydrate supplementation and resistance training. Journal of Strength and Conditioning Research. 2003;17(1):187-96.
4. Kuipers H, Fransen EJ, Keizer HA. Pre-exercise ingestion of carbohydrate and transient hypoglycemia during exercise. International Journal of Sports Medicine. 1999;20:227-31.
5. Thomas DE, Brotherhood JR, Brand JC. Carbohydrate feeding before exercise: Effect of the glycemic index. International Journal of Sports Medicine. 1991;12:180-6.
6. McConell GK, Canny BJ, Daddo MC, Nance MJ, Snow RJ. Effects of carbohydrate ingestion on glucose kinetics and muscle metabolism during intense endurance exercise. Journal of Applied Physiology. 2000;89:1690-8.
7. Tsintzas K, Williams C. Human muscle glycogen metabolism during exercise. Sports Medicine. 1998;25(1):7-23.
8. Steensburg AV, Gerrit K, Charlotte O, Takuya S, Peter P, Bente S, et al. Muscle glycogen content and glucose uptake during exercise in human: influence of prior exercise and dietary manipulation. Journal of Physiology. 2001;541.1:273-81.
9. Wolinsky I,  Hickson J. Nutrition in Exercise and Sport. CRC Press, Boca Raton: 19