Final answer:
A deficiency in muscle glycogen phosphorylase leads to problems with glycogen breakdown, causing muscle weakness, cramps during exercise, and potentially myoglobinuria after intense muscle activity due to impaired energy production in muscles.
Step-by-step explanation:
When there is a muscle glycogen phosphorylase deficiency, a person lacks an important enzyme required for the breakdown of glycogen into glucose during glycolysis. This deficiency can lead to glycogen storage disease type V, also known as McArdle's disease, which is characterized by a build-up of glycogen in skeletal muscles. As a result, affected individuals may experience progressive muscle weakness, muscle cramps during exercise due to an inability to utilize glycogen as an energy source, and potentially myoglobinuria (muscle breakdown products in urine) after intense muscle activity. This condition underscores the critical role of glycogen phosphorylase in the regulation of energy production within muscle cells, especially during periods of high demand such as strenuous physical activity.