Nutrition Science and Everyday Application - beta v 0.1

FUEL SOURCES FOR EXERCISE 555
PHYSICAL ACTIVITY INTENSITY AND FUEL USE
Exercise intensity determines the contribution of different fuel sources used for ATP
production. Both anaerobic and aerobic metabolism combine during exercise to ensure
that the muscles are equipped with enough ATP to carry out the demands placed on them.
The contribution from each type of metabolism depends on the intensity of an activity.
During low-intensity activities, aerobic metabolism is used to supply enough ATP to muscles.
However, during high-intensity activities, more ATP is needed, so the muscles must rely on
both anaerobic and aerobic metabolism to meet the body’s demands.
Activity Intensity Activity Duration Preferred Fuel Oxygen Needed? Activity Example
Very high 30 sec – 3 min Glucose No – anaerobic Sprinting
High 3 min – 20 min Glucose Yes – aerobic Jogging
Low to moderate >20 min Fat Yes – aerobic Walking
Table 10.2. Summary of fuels used for activities of different intensities and durations.
During low-intensity activities, the body will use aerobic metabolism over anaerobic
metabolism, because it is more efficient and produces larger amounts of ATP. Fatty acids
are the primary energy source during low-intensity activity. With fat reserves in the
body being almost unlimited, low-intensity activities are able to continue for a long time.
Along with fatty acids, a small amount of glucose is used as well. Glucose differs from fatty
acids, because glycogen storages can be depleted. As glycogen stores are depleted, the
glucose supply becomes depleted, and fatigue will eventually set in.