Question

Individuals with McArdle's disease has defects in muscle glycogen phosphorylase. As a result, individuals with McArdle's disease have an exercise intolerance with fatigue and cramps, however, after a period of exercise they experience a "second wind" of energy. The second wind results from cardiovascular adjustments that allow glucose to be mobilized from liver glycogen to fuel muscle contraction, though this is less efficient. Choose the ONE best answer below that explains why the amount of ATP derived in the muscle from circulating glucose is less than the amount of ATP that would be obtained by mobilizing the same amount of glucose from muscle glycogen.

Answer 1

In McArdle's disease, muscle fatigue during exercise can be overcome by a "second wind" from cardiovascular adjustments that mobilize liver glycogen. However, the process is less efficient for ATP production in muscles compared to the direct use of muscle glycogen, since more energy is used to transport glucose from the liver to the muscles.

Step-by-step explanation:

Individuals with McArdle's disease have a defect in muscle glycogen phosphorylase, which causes an intolerance to exercise due to fatigue and cramps. However, during exercise, they may experience a "second wind" of energy due to cardiovascular adjustments that allow glucose to be mobilized from liver glycogen to fuel muscle contraction. The amount of ATP derived from this circulating glucose is less than that from muscle glycogen because muscle glycogen is located directly in the muscles and its breakdown for energy occurs without the need for glucose to enter the bloodstream, thus saving energy. In contrast, mobilizing glucose from the liver requires more steps, including its transport in the blood to the muscles, which ultimately consumes more ATP and is thus less efficient.