Which of the following describes an aging-related change in the musculoskeletal system?

The choice referring to bones becoming lighter and more brittle accurately describes a common aging-related change in the musculoskeletal system. As individuals age, a natural decrease in bone density occurs due to factors such as hormonal changes, a decrease in calcium absorption, and changes in bone remodeling processes. This reduction in density makes bones more susceptible to fractures and can lead to conditions such as osteoporosis.

In contrast, the other options describe changes that do not typically occur with aging. Increased bone density is not common; rather, density decreases. Muscle hypertrophy, or an increase in muscle mass, usually requires active training and is not a natural aging process. Additionally, improved joint flexibility does not characterize aging; instead, many older adults experience joint stiffness and decreased flexibility due to factors like cartilage wear and decreased synovial fluid production. Thus, the statement about bones becoming lighter and more brittle aligns accurately with the expected changes in the musculoskeletal system as individuals age.