Walking and running are often-cited examples of "weight-bearing" activities that can help women strengthen their bones and guard against osteoporosis (thinning of the bones). But let's not forget the most obvious form of weight-bearing exercise: strength-training with weights. Following a simple weight-training regimen can do wonders for improving bone density. According to some experts, weight-training exceeds running in its bone-strengthening effectiveness. Only a modest amount of strength training is needed to help the bones: two or three sessions a week, 20 to 30 minutes each, with exercises that work all of the major muscle groups. If you already have some degree of osteoporosis -- or if you're unsure about whether weight training is right for you -- speak with your doctor first.