Fat as fuel during exercise
Carbohydrate (CHO) and fat serve as the two main substrates for the production of energy during prolonged muscle contraction. Although CHO and fat are oxidised simultaneously, the relative contribution of these substrates to oxidative metabolism during
exercise varies, and is dependent on a variety of factors, including exercise intensity and duration and substrate availability and training status, among other factors.
Continuing Medical Education Vol. 26 (7) 2008: pp. 347-349