Optimize your exercise with the right nutrients for the job
Duration and intensity
The type of exercise that someone is participating in determines the types and amounts of food that are necessary to get the job done right. The two main variables that determine these things are intensity and duration of exercise.
Intensity refers to how hard you are working (specifically what percentage of maximum oxygen uptake you are working at).
Duration refers to how long the exercise is taking place.
Intensity and duration are related to each other in the following way: the higher the intensity of the exercise the shorter the duration of the exercise and vice-versa (biologically speaking).
The duration of your exercise determines what kind of fuel your body will primarily use for its activity. When an exercise bout or event is very long (greater than 2 hours of continuous work) the more fat is used for fuel. Up to 60-70% of energy used for exercise lasting 6-10 hours comes from fat. However, in order for the body to use fat for fuel there must be a continuous stream of carbohydrate coming into the body. The body will use stored carbohydrates (glycogen) in the liver and muscle, but once these run out fat can no longer be used for energy. Thus, exercise capacity is greatly reduced.
High intensity short-duration exercise(such as sprinting, all out swimming, all out cycling, and powerlifting) uses anaerobic production of ATP (ATP is the energy source that allows muscles to be contracted). This is because it is the fastest way to get energy to the muscle. In this case glucose (carbohydrates) and glycogen are used for fuel. Glucose or glycogen is used 18-19 times faster anaerobically than aerobically so people performing high intensity exercise or competitive races run the risk of running out of stored glycogen.
People performing very high intensity outdoor activity such as vigorous swimming, cycling, and running should be sure to eat a high carbohydrate meal 3-4 hours before beginning the exercise to optimize performance.
People who perform very long exercise (greater than 3 hours) but with lower intensity such as cycling, jogging, swimming, and hiking should be fine eating a regular diet (such as the one listed below). However, if exercise lasts longer than 6 hours a carbohydrate containing meal will be needed during the exercise to allow further burning of fat for fuel.
Individuals involved in general fitness programs can usually meet their macro nutrient requirements by following a diet of 45%-55% of calories from carbohydrates (1.35g-2.25g per 1LB body weight), 10%-15% of calories from protein (.35g-.45g per 1LB body weight), and 25%-35% of calories from fat (.23g-.68g per 1LB body weight).
Those involved in more vigorous forms of exercise such as vigorous swimming, cycling, or running may need to increase their carbohydrate intake beyond the recommendations above.
When muscles are used the first source of energy that is used is stored carbohydrate in the muscle (muscle glycogen). Once these stores are depleted the body uses stored carbohydrate in the liver and creates more glucose from other substances to fuel the active. Once all stores and substances have been used the body cannot go on. This is what is referred to as “hitting the wall” is commonly. This does not typically happen unless exercise is substantially long. A good example of when this could happen would be a marathon.
Glycogen stores can also be depleted by continuously vigorously exercising multiple days in a row and not replacing the used carbohydrates through diet.
Carbohydrate intake before exercise.
The pre-exercise meal increases performance in two main ways.
- It keeps you from feeling hungry during exercise
- It maintains proper levels of blood glucose for muscles to use for energy.
Without adequate carbohydrate in the blood, muscles, and liver the body cannot perform for long duration's or optimally at any duration. This is where high carbohydrate containing meal comes into play 3-4 hours before beginning to exercise.
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