Orthopaedics & Sports Medicine

During physical activity, the body requires a range of nutrients to generate energy. There are six major classes of nutrients found in food: carbohydrate, protein, fat, vitamins, minerals and water. The first three provide energy for exercise, while the latter three support the body's ability to utilise nutrients effectively. 

Nutritional needs during exercise
The ability to maintain performance during exercise depends largely on the type and amount of nutrients consumed. Nutritional requirements vary according to exercise intensity, age, gender, health status, nutrient reserves and how efficiently the body uses nutrients. 

The body follows a sequence in energy utilisation. In the first six seconds of exercise, explosive muscular force is needed, and energy is primarily derived from the ATP-CP system. Weight lifting is a good example of an activity that relies entirely on this system. 

However, the ATP-CP system only provides short-term energy. From 6 to 30 seconds into exercise, the body begins to use carbohydrate under anaerobic conditions. Aerobic oxidation starts from 30 seconds to 2 minutes, during which both carbohydrate and fat are broken down. Initially, more carbohydrate is used, but after 30 minutes, fat becomes the dominant energy source. 

The type of fuel the body uses depends on both the intensity and duration of exercise. Higher intensity burns more carbohydrate, while longer duration burns more fat. 

Carbohydrate storage and sports performance
Glycogen, stored in muscles and the liver, is the primary source of energy during exercise. Glucose derived from glycogen fuels muscular activity. Muscle glycogen typically supports 60 to 90 minutes of moderate to high intensity exercise, such as a 15 km run. After this, liver glycogen is converted into blood glucose to continue supplying energy. A diet low in carbohydrate results in reduced glycogen stores, which negatively affects endurance and performance. 

For the general population, carbohydrate should make up 45 to 65 percent of daily energy intake. For athletes, this should be around 60 to 70 percent. Prolonged moderate to high intensity exercise can deplete glycogen stores. Research shows that increasing carbohydrate intake 3 to 4 days before exercise can boost liver glycogen storage and improve energy availability. However, this is not necessary for exercise lasting less than an hour. 

Carbohydrate intake should be calculated based on body weight. Individuals should consume 7 to 10 grams of carbohydrate per kilogram of body weight daily. For example, an endurance athlete weighing 50 kg should consume 350 grams of carbohydrate, which may include: 

• 4 bowls of rice or noodles
• 4 pieces of fruit
• 2 glasses of milk or yoghurt
• 1 bottle of sports drink
• 2 bowls of cooked vegetables
• An appropriate amount of meat 
   

Continuous supply during exercise
For prolonged activity, adequate carbohydrate intake is essential to maintain energy levels and reduce the risk of injury due to muscle fatigue. The body requires approximately 35 to 45 grams of carbohydrate per hour during exercise, equivalent to 560 to 750 ml of sports drink. This applies to moderate and high intensity activities such as long-distance running, basketball and football. Consuming foods or drinks with a high glycaemic index (GI) during exercise can quickly raise blood glucose levels, providing fast energy to muscles. 

High GI diet after exercise
After exercise, especially for athletes with back-to-back competitions, it is important to replenish carbohydrate stores. To restore stamina and energy, one should consume 0.7 to 1.5 grams of carbohydrate per kilogram of body weight, roughly equal to one and a half bottles of sports drink. The most effective time to consume carbohydrate is within 30 minutes after exercise, followed by the same amount every two hours for up to six hours. 

Fat
Fat is the main energy source during endurance exercise. The longer the duration, the more fat is burned. For fat loss, prolonged aerobic exercise at low to moderate intensity is most effective. The body primarily uses fat when the heart rate is maintained at 40 to 70 percent of its maximum. As intensity increases, carbohydrate becomes the preferred fuel. For example, brisk walking at 6 km/h for 60 minutes burns more fat than running at 12 km/h for 30 minutes, even though both cover the same distance. 

Studies show that regular exercisers and athletes have more fat-burning enzymes in their blood, allowing their muscles to burn more fat. Unlike carbohydrate, the amount of fat burned is not directly related to fat intake or storage. Fat utilisation is regulated by hormones, so increasing fat intake does not enhance fat burning during exercise. The recommended daily fat intake is 15 to 30 percent of total calories. 

Protein
Protein can provide energy, but it is not the body’s primary fuel during exercise. Only about 5 percent of exercise energy comes from protein, and it is used only when carbohydrate and fat stores are depleted. Increasing protein intake does not directly improve performance, but adequate protein is essential for maintaining muscle mass. 

The general recommendation is 0.8 grams of protein per kilogram of body weight daily. Athletes require 1.2 to 1.4 grams, while bodybuilders may need up to 1.8 grams per kilogram. 

Vitamins and minerals
Vitamins, particularly the B complex, act as coenzymes that help the body process nutrients. Minerals are vital for muscle function, bone health and nutrient transport. Deficiencies in vitamins or minerals can impair physical function and reduce sports performance. A balanced diet typically provides sufficient vitamins and minerals, making supplementation unnecessary. 

Fluids
Adequate fluid intake is essential for the body to function properly and to maintain normal chemical reactions during exercise. Fluids not only improve performance in endurance sports but also support the efficient utilisation of carbohydrate and fat. The body loses a significant amount of fluid during physical activity. Thirst typically begins when around 1 percent of body fluid is lost. At 2 percent, fatigue and dryness may occur. A loss of 5 percent can reduce physical performance by up to 50 percent, highlighting the critical role of hydration in sports. 

Healthy individuals are generally advised to consume 1 millilitre of fluid for every calorie burned. Athletes should aim for a daily intake of 2000 to 4000 millilitres, with additional fluid required during exercise. For example, one should drink approximately 600 millilitres an hour before exercising and 150 to 300 millilitres every 15 to 20 minutes during activity. In hot weather, fluid intake should be increased accordingly. After exercise, it is recommended to replenish 450 to 675 millilitres of fluid for every pound of body weight lost, as indicated by changes in body weight. 

Under normal conditions, water is usually sufficient during exercise. However, for prolonged or intensive activity, sports drinks may be beneficial as they help replenish carbohydrate, fluid and electrolytes simultaneously. Suitable sports drinks typically contain 6 to 8 percent carbohydrate, which equates to 6 to 8 grams of carbohydrate per 100 millilitres of fluid, allowing for optimal absorption.