CPTIPS Nutritional Program
Energy and Cycling
Designing a nutritional program requires an understanding the relationship between energy production to support muscle contractions and the energy requirements of cycling.
Energy is produced by the metabolism (oxidation) of the food we eat (O2 + food). Oxidation provides a high energy molecule, ATP which then powers muscle contractions.
PHYSIOLOGY OF METABOLISM (more detailed discussion)
Energy is stored in the body in fats, carbohydrates, and protein.
Except in malnourished states, protein is not used as an energy source. From this point on, the discussion will be referring to CHO and fats.
- aerobic metabolism - Cellular activity that requires oxygen.
- anaerobic metabolism - Cellular activity that is oxygen independent. Much less efficient than aerobic metabolism.
- lactic acid - One of the by-products of anaerobic metabolism. It has a negative effect on muscle functioning which limits optimum athletic performance.
This energy is released through a chemical reaction with oxygen in a process called oxidation. When oxidation occurs outside the body - for example the burning of oil (a fat) in a lamp or the use of a flaming sugar cube (a carbohydrate) as a decoration in a dessert - this energy is released as heat and light. In the body however, food energy needs to be released more slowly and in a form that can be harnessed for basic cell functions and transformed into mechanical movement by the muscle cells.
Oxidation results in the formation of a single chemical compound adenosine triphosphate (ATP). It is this ATP, synthesized as the cell metabolizes (or breaks down) these three basic foods, that transfers the energy content of all foods into muscle action.
Metabolism can be aerobic or anaerobic.
So you can see that adequate oxygen is necessary to optimally use your fuel reserves. That is why cardiac physiology is so important in understanding metabolism.
- aerobic metabolism - Cellular activity or energy release that requires oxygen.
- anaerobic metabolism - Cellular activity or energy release that is oxygen independent. Much less efficient than aerobic metabolism in terms of the amount of food energy transformed into cellular energy. I.e. less ATP per gram of CHO used
CARDIOVASCULAR PHYSIOLOGY (more detailed discussion)
At levels of exertion greater than the VO2 max., the energy requirements of the cells outstrip the ability of the cardiovascular system to deliver the oxygen required for aerobic metabolism to the individual muscle cells, and oxygen independent or anaerobic energy production begins. Anaerobic metabolism is not only less efficient, with a more rapid depletion of muscle glycogen stores, but also results in a build up of lactic acid and other metabolites that ultimately limit performance even when adequate glycogen stores remain. This lactic acid is metabolized AFTER exercise levels decrease and excess oxygen is again available to the muscle cell. It's degradation is responsible for the oxygen debt or recovery phase that follows anaerobic exercise.
- cardiac output - The volume of blood pumped by the heart (usually expressed in liters/minute). It is the product of the heart rate (beats per minute) and the stroke volume (blood pumped per beat). Approximately 5 to 6 L/min at rest.
- Cardiac Output (stroke volume x heart rate) increases with training but your maximum cardiac output decreases with aging as a result of maximum heart rate decreasing with aging
- Stroke Volume increases with physical conditioning
- A-V O2 difference - The difference in oxygen concentration in the blood being delivered to the organ (arterial) and blood leaving the organ (venous). Expressed as a volume per minute.
- A-V O2 difference increases with exercise intensity. It doubles at maximum exercise intensity compared to rest
- During heavy exercise about 85% of the oxygen is extracted from blood passing the muscle
- oxygen consumption (VO2) - The amount of oxygen (usually expressed as a volume i.e. liters) utilized by an individual for a specified period of time (usually per minute). Approximately 2.5 L/min at rest.
- A measure of exercise intensity. It depends on several factors:
lung capacity (getting oxygen from the air we breath into the blood passing through the lungs), cardiac output (above), and the ability of the muscle cells to extract oxygen from the blood passing through the muscle.
The sum of these factors reflects oxygen uptake per minute by the working muscle.
- Increases with training for any specific heart rate (due to an increase in stroke volume)
- maximal oxygen consumption (VO2max) - The maximum of oxygen that an individual can utilize per minute. It is almost entirely oxygen that is being delivered to the working muscle cells. It is limited by the maximal cardiac output and the A-V O2 difference.
- an individual's upper limit of aerobic (or oxygen dependent) metabolism.
- directly (linearly) related to heart rate i.e. you can use your heart rate as an indirect measure of your %VO2 activity level
ENERGY REQUIREMENTS OF CYCLING (more detailed discussion)
Work, measured in Watts or Calories, is done as one cycles.
At cycling speeds greater than 15 mph, the energy needed to overcome AIR RESISTANCE greatly exceed those of the rolling and mechanical resistance in your bike. For example, in going from 7.5 mph to 20 mph:
- bicycle is very efficient - probably 95% of energy delivered to the wheels
- most work is to overcome air resistance
- exponential relationship to air speed - relationship is an "exponential" one which means that doubling our air speed MORE THAN doubles the Calories expended per mile traveled.
The number of Calories needed for any ride can be calculated - avg. speed of the ride x the time of the ride. Assuming:
- mechanical resistance increases by 225% - small to begin with
- rolling resistance by 363% - small to begin with
- air resistance by 1800%.
the following is a good estimate for replacement Caloric needs for the exercise:
- an average rider (75 kg, 10 kg bike)
- level terrain
For a more detailed discussion of Caloric needs of cycling, go to THE CALORIC EXPENDITURE OF EXERCISE
- 5 mph - 7 Cal/mile - 37 Cal/hr
- 10 mph - 13 Cal/mile - 133 Cal/hr
- 15 mph - 23 Cal/mile - 349 Cal/hr
- 20 mph - 37 Cal/mile - 742 Cal/hr
- 25 mph - 55 Cal/mile - 1374 Cal/hr
- 30 mph - 77 Cal/mile - 2303 Cal/hr
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