John is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Jim is a marathon runner who specializes in long, steady runs. Compared to John's muscles, how are Jim's most likely to differ?
A) Jim's muscles will have more glycogen stored in his type IIb muscle fibers.
B) Jim's muscles will have more mitochondria in his type I and IIa muscle fibers.
C) Jim's muscles will have less myoglobin in his type I muscle fibers.
D) Jim's type IIb fibers will be larger in diameter.
E) Jim will have a greater proportion of type II muscle fibers and a lower proportion of type I fibers than John.

Question

Quizplus · Accepted Answer

Jim's muscles are most likely to have more mitochondria in his type I and IIa muscle fibers, as these fibers are used for endurance activities and require a steady supply of ATP to sustain activity. The presence of mitochondria allows for aerobic respiration to occur and generate a consistent supply of ATP. John's muscles, on the other hand, rely more on anaerobic respiration and the quick breakdown of stored glycogen for their bursts of speed. Therefore, they are likely to have more stored glycogen in type IIb fibers (option A) and larger diameter type IIb fibers (option D), but not necessarily more mitochondria. Option C is incorrect because myoglobin is important for oxygen storage and transport, which is particularly important for endurance activities like marathon running. Option E is also incorrect because research suggests that muscle fiber type distribution is not as clear-cut as previously thought and can be influenced by training and genetics, rather than simply being predetermined by an individual's athletic specialization.

John Is a Sprinter Who Specializes in Quick and Powerful