For years I've exercised fairly intensely six days a week, but now that I'm in my 60s I'm developing more muscle aches and minor injuries. Should I exercise less often, or just less intensely? —J.C.R., Fullerton, Calif.

Both. As you age, your body needs more rest between strengthening sessions and slightly lower-impact activities. At the same time, flexibility training, which helps maintain balance and mobility, becomes more important. Aim to strength-train twice a week, using somewhat lighter weights and more repetitions (10 to 15, rather than the 8 to 12 recommended for younger adults). Rest muscles for two days between sessions. Stretch each muscle group at least two to three times a week, or consider an activity like Pilates, tai chi, or yoga, which combine strengthening, stretching, and balance. And aim for at least four aerobic-style workouts a week, such as brisk walking, cycling, or water exercise.

Read more on exercise for every age group, and check out our interview with "Godfather of Fitness" Jack La Lanne.