Repeated USMLE Questions Step 1- 175

A 23 year-old man visits his physician for a routine examination. He is an Olympic weight lifter. He has no complaints and takes no medications. His medical, surgical and family histories are unremarkable. His muscles undergo hypertrophy and are capable of performing greater forces.

What is the reason of his muscles' hypertrophy and force?

A- Increased length of contractile fibers

B- Increased number of contractile fibers

C- Increased myosin ATPase activity

D- Increased connective tissue content

Answer:







Hypertrophy of muscles due to weight lifting is mainly caused by increased number of contractile fibers (sarcomeres) in parallel to existing units. Length of muscle fibers is limited to its origin and insertion so, it can't increase. Myosin ATPase activity will decrease due to adding more muscle fibers. Connective tissue content will not increase muscle force.

The correct answer is B