When do age-related declines in muscle mass and strength set in?

Muscle mass and strength start to decline around the fourth decade of life and the rate of decline accelerates with advancing age.^[1][2] With that said, the process is heterogeneous in when it begins and the magnitude of decline, especially since lifestyle factors like frequent resistance exercise and adequate daily protein intake can help to delay and attenuate losses in muscle mass and strength with aging. Beyond the age of 50, a loss of leg muscle mass of 1%–2% per year and a loss of muscle strength of 1.5%–5% per year have been reported.^[3]