Final answer:
Sarcopenia is the gradual decrease in the ability to maintain skeletal muscle mass, resulting in a decline in energy-related requirements. Option 4, decreased fat mass and decreased lean body mass, best describes sarcopenia and its impact on energy requirements.
Step-by-step explanation:
Sarcopenia is the gradual decrease in the ability to maintain skeletal muscle mass that occurs in later adulthood. It is characterized by a loss of muscle mass and a decline in muscle strength, which results in a decrease in energy-related requirements.
The best description of sarcopenia that contributes to a decrease in energy-related requirements is option 4: Decreased fat mass and decreased lean body mass. As muscles age, muscle fibers die and are replaced by connective and adipose tissue, which cannot generate force like muscle tissue. This leads to a loss of strength and a decline in energy requirements.