Pre - Post Exercise
All carbohydrates are eventually broken down into glucose, which is then absorbed into the blood stream, where it stimulates the release of a hormone called insulin.
Blood glucose regulation
Insulin enables your muscles and liver to extract the glucose from your blood stream and convert the glucose into glycogen.
Glycogen is stored in the muscle (75%), which is used to provide fuel for the working muscles at a higher intensity.
The remaining 25% of glycogen is stored in the liver to provide a steady supply of glucose to the brain, as are brains are dependent upon a regular supply of blood glucose (6grams per hour) in order to maintain normal conditions.
Low Blood Glucose
Low blood glucose occurs when our body's blood glucose level falls below (160 mg/dl - 9mmols) our fasting blood glucose level.
There are many signs and symptoms that can indicate low blood glucose levels, which all athletes, especially those in endurance events should look out for.
These include, Hunger - Fatigue - Lack of concentration - Irritable - Headache - Nervous - Feeling sick - Poor coordination - Trembling.
The causes for low blood glucose are often straightforward; to avoid these, aim to base your meals on good sources of protein and complex carbohydrates (CHO), eating at regular times.
- Inadequate amount of carbohydrate within your meals.
- Excessive exercise, especially over one hour in duration.
- Low calorie diets.
- High protein diets (Atkins).
- Inconsistency with meal times.
- Missing breakfast, the most important meal of the day, as blood glucose levels will fall during sleep.
- Diabetes (Type 1 - insulin dependent)
Pre-exercise nutrition will require your glycogen stores to be adequately topped up, to avoid early muscle fatigue, and aim to eat your meal two hours prior to training.
Post-exercise nutrition will require depleted glycogen stores to be replaced as quickly as possible, especially during high exercise / racing periods.
After intensive exercise are bodies are able to replenish glycogen at a rate of 7-8% per hour for the first two hours, reducing to a normal level of 5% per hour. For this reason its essential to begin refueling the body in order to maintain high glycogen levels within both your muscles and liver.
Suitable methods of post-exercise nutritional intake.
- Carbohydrates taken with small amounts of protein (3 grams of CHO to 1 gram of protein), will help stimulate the release of insulin in order to synthesis glycogen from available glucose.
- Glycogen is best utilized from intakes of around 50 grams of CHO.
- Aim for initial intake of CHO to have a high glycemic index (easily converted to glucose) i.e. banana, energy drink within the first 15 minutes of finishing exercise.
- After 2 hours of exercise, aim to consume lower glycemic index foods, with protein and fibre to aid absorption.
- Avoid eating excessive amounts of CHO either straight after exercise, or within normal eating habits, as this will place a strain on the bodies conversion ability to convert the glucose to glycogen, resulting in the excess glucose being taken out of the blood stream and converted into fat.