[This is a guest blog by one of our newest interns, Kristen Koltun, a masters sport science student from UNC.]

There has yet to be discovered a definite explanation as to why fatigue occurs, but there are numerous theories. Fatigue refers to the ability of someone to maintain a specific exercise intensity. It is dependent on the type of activity, how trained you are, as well as with environmental and mental factors.

Some physiologically based possibilities include a lack of metabolites or fuel for the working muscles, a lack of oxygen availability or insufficient oxygen transport, or a homeostatic disruption such as dehydration, electrolyte imbalance or hormonal issues. Fatigue may also be related to psychological issues, including pain and discomfort. The most likely theory is one that integrates all other possibilities. In what is referred to as the catastrophe theory, a disruption in any one system will affect all related systems resulting in a simultaneous failure and an inability to keep up with a given intensity or activity.