Patients may have hypertrophy, particularly of the legs, and may have lower bone mineral content and density in the legs.GSD-V patients may experience myogenic hyperuricemia (exercise-induced accelerated breakdown of purine nucleotides in skeletal muscle). The Purine Nucleotide Cycle (PNC) is activated when the ATP (energy) reservoir in muscle cells runs low, and is a part of Protein Metabolism. Adenine (a purine) is converted into AMP (adenosine monophosphate), IMP (inosine monophosphate), and S-AMP (adenylosuccinate) in a circular fashion; the byproducts are fumarate (which goes on to produce ATP via oxidative phosphorylation), ammonia (from the conversion of AMP into IMP), and uric acid (from excess IMP). To avoid health complications, GSD-V patients need to get their ATP (energy) primarily from Free Fatty Acids (Lipid Metabolism) rather than Protein Metabolism. Over-reliance on protein metabolism can be best avoided by not depleting the ATP reservoir, such as by not pushing through the pain and by not going too fast, too soon. "Be wary of pushing on when you feel pain start. This pain is a result of damaging muscles, and repeated damage will cause problems in the long term. But also this is counterproductive--it will stop you from getting into second wind. By pressing on despite the pain, you start your protein metabolism which then effectively blocks your glucose and fat metabolism. If you ever get into this situation, you need to stop completely for 30 minutes or more and then start the whole process again.
Glycogen storage disease type V (GSD5, GSD-V), also known as McArdles disease, is a metabolic disorder, one of the metabolic myopathies, more specifically a muscle glycogen storage disease, caused by a deficiency of myophosphorylase. Its incidence is reported as one in 100,000, roughly the same as glycogen storage disease type I.The disease was first reported in 1951 by Dr. Brian McArdle of Guys Hospital, London. Signs and symptoms
The onset of this disease is usually noticed in childhood, but often not diagnosed until the third or fourth decade of life. Symptoms include exercise intolerance with muscle pain, early fatigue, painful cramps, inappropriate rapid heart rate response to exercise, and may include myoglobin in the urine (often provoked by a bout of exercise). "In McArdles, our heart rate tends to increase in what is called an inappropriate response. That is, after the start of exercise it increases much more quickly than would be expected in someone unaffected by McArdles." Myoglobinuria may be seen due to the breakdown of skeletal muscle known as rhabdomyolysis, a condition in which muscle cells breakdown, sending their contents into the bloodstream.