After the age of 35, muscle mass and strength gradually decrease. After age 60, the declines in muscle function are even more rapid.
The good news is that this decline can be prevented by some simple lifestyle changes. Research indicates that resistance exercise is especially important.
Also, adequate energy intake, especially protein, is important. In fact, it has been questioned whether the dietary reference intake for protein (0.8 g per kg/day) is adequate for older individuals. Some argue they may need more than 1.0 g/kg/day. Some research also indicates that unlike younger individuals, older adults may respond better to protein alone rather than protein with carbohydrates. The combination of consuming protein alone and weight training appears to be the best defense against muscle loss that occurs with aging.