Final answer:
Muscle mass increases BMR because muscles are metabolically active, whereas BMR decreases with age due to muscle mass loss. Men typically have higher BMR than women due to more muscle mass. Regular exercise can mitigate some of the BMR decline by building lean muscle.
Step-by-step explanation:
How Muscle Mass Affects BMR
Muscle mass significantly affects Basal Metabolic Rate (BMR) because muscle tissue is more metabolically active than fat tissue. Therefore, individuals with greater muscle mass have a higher BMR, which means they burn more calories at rest. As a person ages, their BMR generally decreases, largely due to a reduction in lean muscle mass. After the age of 20, the average BMR decreases by about 2% per decade. This decline is even more pronounced between the ages of 50 and 70, when muscle loss can lead to a substantial drop in BMR, further exacerbated by reduced physical activity levels.
Changes in BMR Over Time
The gradual reduction of BMR with age is influenced by changes in body composition, such as a decrease in muscle mass and strength. This not only slows down the metabolism but also tends to discourage seniors from engaging in physical activity, creating a cycle of further muscle and BMR reduction. However, regular exercise can help to build lean tissue and raise BMR, offsetting some of the impacts of aging.
Gender Differences in BMR
Men typically have a higher BMR than women because they generally possess more muscle mass. Additionally, the decrease in women's BMR between the ages of 5 and 17 is faster compared to men. It's important to note that factors such as body composition, hormone levels, and genetic makeup also play significant roles in determining an individual's BMR.