NOT all exercises strengthen bone. To reduce fracture risk, exercise must be weight-bearing. Your bones must support your weights as they do when you walk, run, dance, garden, or do housework.
Activities that are not weight-bearing, swimming and cycling for example, are great fun and have many health benefits. But they do not reduce fracture risk.
Weight-bearing exercise helps prevent fractures at any age. While most studies have targeted middle-aged or older people, several have correlated exercise and fractures among adolescent and young adults. In young girls and boys, in teenagers, and in young adult military recruits, regular, moderate activity reduces fracture risk significantly. Walking puts weight on the legs and spine. It helps prevent hip and vertebral fractures. But what about arm and wrist fractures? Effective approaches include gardening, which involves carrying things, and the yoga poses that put weight on the wrist and arms. You can also carry light weights, such as canned foods, while you walk or lift weight, including unloading groceries or a dishwasher.
Bones are similar to muscles. Use muscles, and they become bigger and stronger. Stop using them, and they weaken and atrophy. Like muscles, when bones are used, when they support weight or carry a load, they get stronger. When we use our muscles, they develop microtears. We repair these tears by creating new muscle tissue which is why sustained exercise produces bigger, bulkier muscles. Similarly, when our bones bear weight, they experience strain. Strain produces microscopic weak spots. As those weak spots develop, the bone cells in the vicinity release chemicals that signal the body: Weak spot! Send help! Bone-clearing osteoclasts onverge on the problem area and dissolve the weakened bone. Then osteoblasts migrate from nearby bone marrow, enter the tiny breach, and create a new bone. Normal strain stimulates the creation of new, strong, robust bone. In other words, weight-bearing activities give bones a reason to thrive.
In the absence of normal strain, when bones don’t support weight or content with the torque and impact of activities like walking, very little new bone is created. Old bone slowly weakens and over time becomes prone to fracture. Most bone building takes place as the body reacts to changing or “dynamic” strain. Stand still for an hour and the hip and leg bones experience some strain. But it’s static strain. It doesn’t create much new bone. Walk for an hour and the strain is dynamic as we step, turn, climb, crouch, descend, and stretch to accommodate the terrain. That’s why walking is a prime bone builder.
Many people believe that to improve health exercise must be aerobic, strenuous enough to raise the heart rate considerably. It’s wrong. Aerobic exercise is too strenuous for most people and some just don’t enjoy it. Aerobic exercise also raises risk of injury. Aerobic conditioning is necessary only if you’re determined to excel at highly competitive sports. If you’re not a competitive athlete, if your exercise goal is health not trophies, then non-aerobic exercise is sufficient, assuming you do it
regularly, ideally daily for at least half an hour. Nonaerobic exercise strengthens bone, improves sleep, controls weight, elevates mood, enhances sex, and reduces risk of obesity, diabetes, high cholesterol, high blood pressure, heart disease, Alzheimer’s and many cancers.
Many studies have shown that regular, non-aerobic exercise provides all the health benefits of strenuous aerobic workouts. Walking, gardening, dancing, yoga, etc. offer two major advantages over aerobics, they are less strenuous, so people are more likely to stick with them, and non-aerobic exercise is less likely to cause injury so people can stick with it. Telling everyone they had to engage in strenuous aerobic workouts at least three times a week to obtain health benefits from exercise is a mistake. Regular, moderate exercise is enough. An active lifestyle does not require vigorous exercise. Small lifestyle changes that increase daily activity are sufficient.
With walking, there’s nothing to learn. You’re already good at it. You don’t have to join a gym. There’s no clothing or equipment to buy. You can carry on a conversation while walking, so it’s sociable, a great way to spend time with friends. Just put one foot in front of the other and repeat. The key to walking for stronger bones and better health is regularity. A half hour every day is preferable to one four-hour hike a week.
Obesity is bad for the health but it reduces fracture risk. Obesity shortens life expectancy because it increases risk if diabetes, high cholesterol, high blood pressure, heart disease, stroke and many cancers. But according to many studies, fractures are much more likely in those who are underweight (especially frail) then overweight. Extra weight means more bone strain during weight-bearing exercise and as a result, more new and stronger bones. In some way this is counterintuitive. People who are obese may eat a diet high in animal foods, fast food, and junk food and low in fruits and vegetables. That diet increases fracture risk. People who are obese also tend to be sedentary. Lack of exercise increases fracture risk. People who are obese often develop type 2 diabetes, a major risk factor for fractures.
Nonetheless, being overweight or obese reduces fracture risk. Why? Because despite all the reasons why obesity should increase fracture risk, extra weight increases bone strain and bone formation. Decreased fracture risk is no reason to become overweight. But it shows how important weight-bearing exercise is to bone strength and fracture prevention.
