Basically, as you get older your muscles become resistant to the normal anabolic stimulants - resistance training etc. Maintaining muscle is very important as we age - it is vital to function and to supplying a range of raw materials for the metabolism, not least in terms of immune response. So we need to understand how to do that, how to keep our muscle.
The key recommendation seems to be to combine resistane training with branched chain amino acids. Incidentally something that Art Devany has recommended for a while.
Skeletal muscle protein metabolism in the elderly: Interventions to counteract the 'anabolic resistance' of ageing