There's no need to be weak and frail. You can actually do a lot about physical deterioration ... up to a point. In one of the triathlons I raced last year the retired Marine who won the 70 - 79 age group was only a few minutes slower than me.

The key to staving off muscle atrophy and loss of bone mineral density is doing high-impact training and weightlifting at least a couple times per week, while maintaining proper form to avoid injury. The digestive system also becomes less efficient at absorbing some nutrients so you have to increase protein intake in order to have the necessary building blocks for repairing damaged muscle tissue.