Why not just rely on Carbohydrate (Glucose) as my fuel source?
Carbohydrate
is used as fuel by muscle cells in the form of blood
glucose, and has a very limited supply. We keep reserves of Glycogen in
muscle and liver tissue that can be tapped for conversion to blood
glucose, but it is also a limited supply, so if we are exercising or
racing at an intensity that utilizes carbohydrate as the predominant
fuel source, we will run out of fuel and "bonk," or "hit the wall."
Understanding how your
body utilizes fat versus carbohydrate is important in making
fueling decisions for training or racing, and may dictate the best
maximum aerobic intensity that an athlete can sustain for a given
endurance event. An assessment such as a Metabolic Profile provides a graph showing exactly
how
much fat and carbohydrate are being utilized at any given exercise
intensity, and where your Crossover point (Aerobic Base) is. With
periodic testing an athlete can monitor their progress and make
adjustments to their training and racing strategy.