According to a recent New York Times article, The Best Exercise for Aging Muscles:

The toll that aging takes on a body extends all the way down to the cellular level. But the damage accrued by cells in older muscles is especially severe, because they do not regenerate easily and they become weaker as their mitochondria, which produce energy, diminish in vigor and number.

The good news is exercise can mitigate some of the effects of aging by improving the cellular health of muscles, slowing the loss of muscle mass and boosting bone density. Try these top exercises to keep bones strong and healthy as you age.

Interval exercise – Mayo Clinic researchers found that study participants older than 64 realized significant benefits from HIIT or high intensity interval training. In fact, these participants saw greater gains in the number and health of mitochondria (responsible for generating energy for muscle cells) than did participants that trained with weights.

How to do it: HIIT alternates periods of high intensity exertion with periods of rest or low intensity. For example, using an exertion scale of 1 to 10, with 10 being the highest effort, you could run at an 8 to 10 effort for two minutes then at a 1 to 2 effort for 30 seconds repeat for desired number of cycles. You can adjust the length of periods of intensity and rest depending on your fitness level and how much time you have for exercise.

Weight training – Weight training is a good complement to interval training because it builds muscle mass, which we lose with age. On average, without intervention, we lose about six percent of muscle mass with each decade after forty. Interventions are important because they help us maintain healthy weight. Muscle contributes to a healthy metabolism and helps us burn more calories at rest than fat foes. Without muscle mass, we also lose strength and functional fitness, so everyday tasks become more of a challenge.

How to do it: Prevention magazine advises newbies to fuel up properly (think protein, complex carbs and fiber) to support a weight training regimen. Also recommended is attention to proper form and pacing. Don’t try to do too much too soon or you will risk injury. Start with smaller weight that allow you to learn and maintain proper form before moving onto heavier weights.

Body weight exercise – Body weight exercise reduces the risk of falls with aging and can also protect against osteoporosis. You won’t need any special equipment to build more bone density. Just find something you love and do it often. There are lots of great things you can do, including:
Tai Chi
Stair Climbing

You get the idea. Just get up and get moving to improve bone density. Exercise can significantly improve functional fitness and quality of life as we age. Aim for variety so interest and motivation stays high.