We've talked about the nutrients we use to produce ATP. Theses nutrients gets converted to ATP based on the type of activity we are performing, the duration and intensity.
Carbohydrates fuel moderate to high intensity exercise, while fats are utilised during endurance events. They are not adequate for high intensity training, such as sprints or intervals.
During low intensity exercise (less than 50% maximum heart rate) there is enough energy stored in the body to fuel it for hours each day, providing we have enough oxygen to allow fat to be metabolised.
With an increase in intensity carbohydrate metabolism kicks in. This is more efficient, but has limited stores. We can sustain moderate to high intensity exercise for approximately 2 hours with stored carbohydrates (glycogen). Once our carbohydrates stores are depleted and fuel isn't replace we need to stop. Carbohydrates are able to produce approximately 20 times more energy (ATP) per gram when adequate oxygen is available to help it metabolise, than in an anaerobic environment where there is no oxygen, which occurs during high intensity activities.
As exercise intensity increases the efficiency of carbohydrate metabolism decreases and we start to utilise the anaerobic system. This is because the body cannot take in and utilise enough oxygen to metabolise either carbohydrate or fat.
During digestion carbohydrates are converted to glucose, fats to fatty acids and proteins to amino acids. They are absorbed into the blood and transported to:
- Glucose (glycogen) - muscles and liver
- Fatty Acids (Body fat) - adipose tissue
- Amino Acids - the growth and repair of muscles or excreted as waste. These we don't store
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