What is sarcopenia?

• A. Age-related increase in muscle mass.
• B. Disease-related loss of motor neurons only.
• C. Acute inflammation of muscles due to exercise.
• D. Age-related loss of muscle mass and strength due to motor unit loss, fiber atrophy, and decreased regenerative capacity.

Answer: (D)

Sarcopenia is an age-related decline in skeletal muscle mass and function. It happens through several interconnected changes: loss of motor neurons leads to fewer motor units, and some muscle fibers become denervated while others are reinnervated, but overall there’s a net decrease in muscle fibers. In addition, individual muscle fibers shrink (fiber atrophy), especially fast-twitch fibers, which reduces force production. Aging also brings a diminished muscle-regenerative capacity because satellite cells become less responsive and anabolic signaling declines, making repair and growth after minor injuries less effective. Put together, these factors cause both less muscle mass and weaker muscle power, which is what sarcopenia describes.

An increase in muscle mass with age isn’t sarcopenia, so that option doesn’t fit. Sarcopenia isn’t solely about disease-related motor neuron loss, but rather a multifactorial, gradual aging process. It isn’t an acute inflammatory response to exercise, which is temporary and situational, not the chronic decline described here.