Role of fats (Adipose Tissue) in exercise. FFA Utilization.
 Why you should do a % of your LONG DURATION endurance training in a "Un Fed State", NO CARB'S.

Muscle FFA's (free fatty acids) are oxidizable lipid fuel sources for skeletal muscle metabolism
during prolonged exercise. FFAs are a major fuel oxidized by skeletal muscle, and their rate
of use by muscle depends on several factors, including plasma FFA availability, transport from
to the mitochondria, and intracellular metabolism. Mobilization of FFAs from adipose tissue
is the first committed step in FFA metabolism, and it depends on the rate of adipose tissue lipolysis.

Adipose tissue lipolysis increases with exercise duration and exercise intensity up to
intensities of approximately 60% to 65%. Evidence suggests that FFAs are transported
from plasma to the mitochondria by FFA transporter proteins that include the plasma membrane.

Plasma FFA use can also be regulated at the mitochondrial transport step by changing the activity
of carnitine palmitoyl transferase (CPT-1). Although results from biopsy and tracer studies indicate
that muscle TG (triglyceride) contribute to skeletal muscle oxidative metabolism during
exercise, their exact contribution is difficult to ascertain. Evidence shows that muscle TG use
depends on exercise intensity, duration, and mode. (Low Intensity, Long Duration and Steady State)

The contribution of plasma TG to skeletal muscle metabolism is small. The rate of use of plasma
TG is dependent on lipoprotein lipase activity, which is correlated with the oxidative capacity of
the muscle fibers.

Dietary manipulations can modulate substrate use during exercise and can potentially affect
exercise performance. High carbohydrate availability before exercise is associated with an increase
in blood glucose and plasma insulin concentrations, which can ultimately decrease the rate
of adipose tissue lipolysis and the availability of plasma FFAs.

Increased glucose flux has also been shown to decrease lipid oxidation by directly inhibiting the
transport of FFAs across the mitochondrial membranes. High lipid availability can be changed
by short-term or long-term exposure to high-fat diets. Because carbohydrate reserves are
diminished with exposure to high-fat diets, improvements in exercise performance have
been difficult to measure under these conditions.