The science is increasingly clear: Older adults need both strength training, to help replenish and maintain the muscle mass and (for women especially) the bone density our bodies lose each year as we age, and cardio to help guard against the risks of clogged arteries in the heart and brain.

WSJ: Exercise in Retirement: Cardio vs. Weight Training

This, in turn, limits a person's peak bone mass in adulthood, making osteoporosis a greater threat when bone density starts to decline late in life.

FORBES: DeCode Discovers Osteoporosis Gene

The control group showed a decrease in soleus muscle mass and strength, the development of insulin resistance, and a loss of bone mineral density and resistance to breakage.

FORBES: Didn't Have Time to Exercise? Drink Some Red Wine.