Carbohydrate as an Energy Source Depending on Types of Activity

Why do you think that carbohydrate is an important source for exercise? Carbohydrate is mainly energy food for exercise because it can be used for anaerobic energy production when the oxygen level is low. In terms of caloric value, carbohydrates yield less energy (1g = 4 kcal) compared to fat (1g = 9 kcal). However, carbohydrate appears to be a more efficient fuel than fat because more oxygen is required to metabolize the fat. In every one litre of oxygen, we will find that carbohydrate produces about 5.05 kcal while fat gives only 4.69 kcal.Carbohydrate or to be specific, glucose used during exercise depends on the intensity and duration of the activity. It becomes the major contributor of energy for contracting muscle at intensity more than 50-60% of VO2max. What happens is that, in the first 10 minutes, our body will rely solely on the glycogen stores. As the exercise is prolonged, we will use up to 20% of the available glycogen. For people who exercise longer than 20 minutes, their body
will start to use more fat for fuel compared to glucose. The summary of the correlation between activity intensity and nutrients used are as follows:

1. During very light exercise, for example walking at the low intensity
level, fat is used as an important energy source.

2. During moderate exercise, the source of fuel shifts from fat to
carbohydrate. The usage of carbohydrate increases to 50 % or more.

3.During high intensity or vigorous exercise or at 65-85 % of VO2max,
carbohydrate becomes the most preferred energy source.

Thus, carbohydrate is the key energy source for high-intensity anaerobic event lasting for less than two minutes and high-intensity aerobic activity lasting more than an hour or two. Carbohydrate is also an important energy source for stop-and-go prolonged sports such as football, hockey, rugby, tennis and squash.