Nutrition Before Exercise Glycogen Loading

Muscle glycogen depletion and low blood glucose levels have been shown to be major factors in the development of fatigue during endurance exercise. Therefore, it is important to ensure optimal glycogen storage prior to exercise and optimal delivery of carbohydrate (CHO) during exercise.

Of crucial importance in the pre-competition preparation of an endurance athlete is defining the best method to optimize the body's glycogen levels. In the past, Scandinavian researchers introduced a supercompensation diet. Their recommended strategy and diet is as follows. One week prior to an important race, a bout of exhausting endurance exercise is performed in order to deplete the glycogen stores. Over the next 3 days a high fat diet is ingested, ideally with less than 20% of the energy intake as CHO. During the remaining period leading up to the race, the athlete should ingest a high CHO diet with less than 20% of the energy intake being derived from fat. No endurance training should be undertaken during the 6 days prior to the race. This diet training regimen leads to a large increase in the muscle glycogen stores (160-200% greater than the normal resting levels). However, this protocol has serious disadvantages:

  • During the high fat, low CHO period, athletes often feel weak and sometimes become unmotivated and lose self-confidence.
  • For some athletes it may be difficult to compose a palatable diet consisting of only 20% of the energy from fat (or 20% of the energy from CHO), and a good working knowledge of the CHO and fat content of foods is required.
  • The high fat diet may cause gastrointestinal problems such as diarrhoea or abdominal cramping in some athletes.
  • Many athletes are reluctant to abstain from training for 3 -7 days prior to an important competition.

Because of these disadvantages, a more moderate and more practical dietary training regimen has been evaluated. This regimen also begins with a bout of exhausting exercise 1 week before the race. However, during the 6 days that follow, it is recommended that the dietary CHO intake be progressively increased from the usual 50-55 en% to about 70 -75 en%. Over the same period, it is advocated that the training volume is gradually decreased without changing the training intensity: this is called tapering.

This protocol also results in significantly increased glycogen stores (150% of normal resting value) (172), without the side effects so often reported by athletes using the classical regimen. A graphical comparison of both treatments is shown in Figure 48.

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