Which life stage is associated with declining muscle mass and increasing body fat?

• A. Late adulthood
• B. Middle adulthood
• C. Early adulthood
• D. Infancy

Answer: (B)

As people age, lean muscle mass tends to decrease while fat mass tends to increase. This shift starts to become noticeable in middle adulthood due to factors like reduced muscle fibers, lower protein synthesis, and a drop in anabolic hormones, along with a slower metabolism and often decreased activity. Because this pattern of declining muscle mass with rising body fat commonly begins during middle adulthood, it’s the best fit for the question. Infancy is a growth phase with rapid gains in both muscle and fat, and early adulthood typically maintains peak muscle mass, while late adulthood shows more pronounced changes but the onset is earlier.