Although bones may seem to be rigid and fixed, they are actually more like muscles, capable of growing or shrinking with use. Each time a bone is moved, it bends ever so slightly, just enough in fact to trigger electrical and biochemical changes that stimulate bone formation. The more force, the greater the bending, and the greater the stimulus for new bone formation. A normal amount of movement keeps the density of bone constant, while additional bending say, from a brisk walking routine-can cause bone mass to increase. Less frequent bending, on the other hand, signals to the body that it doesn't need so much bone mass. When a wrong message like this is sent out, the bones become thinner and more brittle.

Although the ability to increase bone mass is going to vary from person to person with age and gender, everyone can benefit from exercise and a balanced, calcium-rich diet. Here are some easy suggestions to follow for a healthier and more upright skeletal structure.

- Walk, jog, run, play, move or dance. Any activity done in an upright position helps because muscles and bones work together against gravity to hold our frames erect. Swimming and biking, while great for the heart, don't do very much for the bones.

- Lift weights. The benefits of weight-bearing exercise can be enhanced by strengthening specific muscle/bone groups.

- Exercise moderately 3 to 5 times every week, for at least half an hour each time. Although there are no clear guidelines for maintaining bone mass, this amount of aerobic exercise is a good guide to follow.

- The public has been repeatedly encouraged by the American Dairy Council to drink more milk every day for stronger bones and teeth. But the adult human body lacks the necessary enzyme to properly digest milk. As a result, most of those who drink a lot of milk tend to have mucus accumulation problems in their upper respiratory systems. Much safer alternatives would be tofu milk, calcium-enriched soy milk, and goat milk. And unless a person has hypoglycemia, calcium-fortified orange juice is good. A juice mixture made from one cup each of kale and collards and 1 1/2 cups of pineapple juice, mixed together for two minutes in a Vita-Mix Whole Food Machine, is an outstanding drink for strengthening the bones in older people. (See Product Appendix for more information on the Vita-Mix.)