What factor can decrease muscle mass as individuals age?

As individuals age, one significant factor that can lead to a decrease in muscle mass is reduced physical activity. This decrease in activity levels often results in a condition known as sarcopenia, which is characterized by the loss of muscle mass and strength. When an individual is less active, their muscles are not routinely engaged in resistance or strength training, which is essential for maintaining muscle health.

Physical activity, particularly weight-bearing and resistance exercises, stimulates muscle protein synthesis and helps to preserve and build muscle tissue. Without adequate physical activity, the body's demand for muscle adaptation decreases, often resulting in a gradual decline in muscle size and strength. Additionally, older adults may experience a natural decline in hormones, such as testosterone and growth hormone, that are instrumental in muscle maintenance, further exacerbating the effects of inactivity.

The other factors mentioned, such as increased calorie intake or enhanced protein synthesis, would typically not contribute to a decrease in muscle mass. Shorter sleep duration can impact recovery and overall health but is not as directly linked to muscle mass decline as reduced physical activity is. Thus, maintaining an active lifestyle is crucial for preserving muscle mass as one ages.