Kate Morland, Nutritionist
Are you looking to take on a new sporting challenge but unsure how to fuel yourself?
During bouts of intense exercise lasting up to 3 minutes, our muscles are fuelled anaerobically (without sufficient oxygen) and predominantly utilise glucose. The combination of depleting glucose stores and the production of lactic acid results in muscle fatigue.
During longer bouts of exercise, there is sufficient oxygen supply to enable the aerobic pathway to provide energy. In addition to glucose, fatty acids (fat stores) and amino acids (protein stores) are burned as fuel. However, because glycogen stores are limited, there will be a point during longer duration exercise (more than 90minutes) where glycogen stores become depleted. Fatigue occurs because there is not enough blood glucose available to compensate for the depleted muscle glycogen.
Glucose is the basic building block of carbohydrates. When we eat carbohydrates, they are digested to release glucose. Glucose is freely present in our blood stream and also stored in the form of glycogen by the muscle and liver. There is a limited capacity for our body to store glycogen (approximately 250-500g in a 50-70kg adult)(1). Glucose is in hot demand not only by the muscles but for the brain and nervous system.
The use of glucose drinks during exercise helps athletes to keep blood glucose levels elevated and provide carbohydrates to working muscles. A glucose containing drink is also helpful to aid recovery after exercise. It will replenish glucose levels in the blood and promote glycogen replacement.
A sports drink with a concentration of 4-8% of glucose or glucose-containing carbohydrates is optimal. Current recommendations for exercise lasting greater than 90 minutes suggest 30-60g of carbohydrates per hour during exercise will offset depletion and fatigue(1). It is best to take this at regular intervals throughout the hour.
Protein is our building block for our muscles. The general person consumes enough protein from their diet however in stressful situations such as during exercise, your protein requirements are increased. Consuming a protein rich shake is a convenient way to achieve this. Vitaplan is a low cost option that also provides carbohydrates and vitamins and minerals to support recovery and weight gain.
It is important when undertaking exercise lasting greater than one hour, or in particularly warm climates, to consider replacing electrolytes that will be lost through sweat and metabolism. Sodium facilitates the uptake of water and sports drinks should contain 0.5-0.7 g/L (20-30mmol/L) (1).
Date:Monday, 21 February 2011