While certain types of exercise increase bone density, the current debate is over the type of exercise that increases it most effectively. Several studies have demonstrated that five key exercises improve bone density in the hip and spine and therefore are effective in the battle against osteoporosis. These exercises are lunges, squats, chair raises, stepping and toe raises.
The phrase “weight-bearing exercise” has become an increasingly popular way to help people understand bone-building exercises, but it doesn't fully explain the type of stimulus bones need. To increase bone density, exercise must be different from and greater than daily activities. If you have been inactive and start a walking program or switch from walking to running, your bones will initially respond by improving density, but after a couple of weeks, the stimulus becomes normal and your bones no longer need to adapt. Bone density responds better to short bouts of increased mechanical loading. In other words, ongoing repetitive movements common to aerobic exercise are not effective at increasing bone density, even if they are weight-bearing activities. After the first minute or so of repetitive loading, the cellular response of bones switches off. On the other hand, lunges and squats are the kind of weight-bearing exercises that do build bone density.
To increase bone density, you have to surprise the skeletal system with diverse exercises that require unfamiliar loading patterns or changes in movements. Your bones will adapt to new and different forces from a variety of angles, but only the bones that are directly stressed will adapt. The two primary ways to add stress to bones are to increase force and add impact. Squats increase force by tugging on the muscles that attach to the bones. Forward, diagonal and side lunges increase force by tugging on the bones from different angles. They also add impact when you step down into the lunge.
Both squats and lunges are compound exercises, meaning they incorporate multiple movements and use more than one joint. Because of this, they are often difficult to perform correctly in the beginning, before your neuromuscular system is familiar with the motion. It's a good idea to have a personal trainer or physical therapist evaluate your form. Start simply and perfect your form before increasing the difficulty. To safely squat, keep your knees aligned over your ankles throughout the squat. The easiest way to do this is to squat with your calves against a chair. Squatting with your toes and knees facing forward and your feet greater than hip-width apart will increase balance during the squat, place less stress on your knees and improve strength in your hips. To lunge safely, keep the lunging knee aligned over the ankle. Lunging up onto a step will place less stress on your knees.
Once you can easily repeat three sets of 15 repetitions without pain, advance to more difficult variations, switch between exercises in a set and vary the tempo. You can also start adding weight in 1- to 2-pound increments. To add weight, hold dumbbells or wear a weighted belt or vest. For each new weight, start with one set of 10 to 15 repetitions and work up to three sets of 15.