CPT deficiency is one of a group of metabolic muscle diseases that interferes with the processing of food (in this case, fats) for energy production.
Symptoms usually are brought on by prolonged and intense exercise, especially in combination with fasting, but may not appear for several hours after activity stops. Short periods of exercise usually don’t provoke symptoms.
Symptoms also can be brought on by illness, cold, stress or menstruation. This disorder causes muscle pain, stiffness and tenderness, while weakness is less common. Breakdown of muscle tissue during an attack can cause myoglobinuria (rust-colored urine).
To learn more about the effect of diet in this disease, see What Not to Eat: Some consensus, much controversy about diet in three metabolic diseases. 
This condition is caused by a genetic defect in the carnitine palmityl transferase 2 enzyme (CPT2), which normally escorts breakdown products of fats from the main part of the muscle cell into the mitochondria (the cell's "engine"), where they can be further metabolized for energy. See Causes/Inheritance .
If the CPT2 enzyme is completely lost, this disease has a rapid progression leading to death in infancy. If some enzyme activity remains, there is little or no progression with normal strength between episodes.
Researchers on metabolic diseases of muscle are making progress on a number of fronts, including: