Lacking physical activities in older adult could cause which of the followings.

Sedentary behavior triggers sarcopenia, which is the involuntary loss of skeletal muscle mass and function. Reduced mechanical loading leads to myofibrillar atrophy and decreased metabolic rate. This condition increases the risk of mobility impairment and falls in geriatric populations. Rationale: A. Inadequate physical activity does not directly result in a protein deficiency, which is primarily a nutritional or malabsorptive issue. Although exercise influences protein synthesis, the lack of movement does not deplete the body's essential amino acid stores or dietary protein levels. B. Vitamin levels are governed by dietary intake and metabolic absorption rather than physical exertion. A vitamin deficiency like low vitamin D is related to UV exposure or diet, not the mechanical movement of the musculoskeletal system or physical inactivity. C. A joint infection, or septic arthritis, is an inflammatory condition caused by pathogens like Staphylococcus aureus. It is an acute infectious process and is not a physiological consequence of a sedentary lifestyle or lack of regular physical exercise. D. Chronic inactivity leads to significant muscle weakness through the reduction of Type 2 muscle fibers. The lack of resistance and movement results in atrophy, which compromises postural stability and reduces the functional capacity required for activities of daily living.