Not exact matches
The conversion of calories from their stored nutrient state to the
form that can be burned by your muscle cells is achieved,
during aerobic exercise, through the process of cellular
respiration, which requires oxygen, and the delivery of oxygen through your bloodstream to your active muscle cells is directly related to your heart rate.
Cardiorespiratory fitness is a measure of how well your body is able to transport oxygen to your muscles
during prolonged exercise, and also of how well your muscles are able to absorb and use the oxygen, once it has been delivered, to generate adenosine triphosphate (ATP) energy via cellular
respiration (cellular
respiration is a chemical process in your body's cells that converts the energy stored in the food you eat into the ATP
form of energy that is recruited for use by your muscles).
For many athletes looking to get into distance running and experiencing difficulty performing at peak, other factors such as hydration, running
form (and therefore injury / discomfort / cramping
during a long race), glycogen stores,
respiration, etc. all fail long before their theoretical limit is reached.