Aging impacts metabolism and fitness capacity, causing a natural decline in muscle mass, strength, and aerobic capacity. This results in a slower metabolic rate, making it easier to gain weight if diet and activity levels remain unchanged. Additionally, hormonal changes, like decreased testosterone and estrogen, contribute to shifts in body composition. To counteract these effects, it is essential for older adults to engage in regular strength training and maintain cardiovascular health through aerobic activities, which can help preserve muscle mass and enhance overall fitness.