By Wendy Kohrt, PhD (Member, Medical and Scientific Advisory Board)
We often hear that weight-bearing activity is critical for bone health, but many people don’t know what that means or how to achieve it. If you watch children play, they’ve got it right! Running, jumping and cartwheeling are the kinds of activities that help them build bone.
Weight bearing, or loading, adds a stress to the bones that stimulates bone building. The load slightly compresses the bone matrix and triggers the cells to take in more calcium and other minerals, and ultimately to increase bone density. The amount of weight that causes this response from the bone is called “osteogenic loading” because it takes a certain “load” to stimulate the bone-building cells. In contrast, “unloading” the bones — prolonged bed rest or space travel, for example — can result in loss of bone mineral density. While normal daily activities are sufficient to prevent the harmful effects of unloading, significant “loading” appears to be required to increase bone density.
We measure activity by how many multiples of body weight are loaded onto the skeleton. Scientists in the United Kingdom, using accelerometers, did a cross-sectional study in children that found the amount of loading required to stimulate the bone-building process equals 4.2 times body weight.
As with all exercise studies, it is difficult to control for all of the variables associated with the participants, so we must be careful in generalizing the results to other populations.
When we stand, gravity applies a load to our bones that equals our body weight. Walking briskly increases load, and running or jogging adds even more load, but we need higher-impact activities like jumping or strength training to add four or more times our body weight.
Always begin loading activities at a level that is right for you. As you train to walk in the Susan G. Komen 3-Day, work to increase your walking stride. If you are running, consider adding higher-impact activities. Weight or resistance training is beneficial to muscle, and with enough load, it can stimulate bone building as well. Avoid excessive loading to prevent injury.
If you have low bone density or osteoporosis, work with a professional on any activity that will add load to your bones. You want to use proper form and body mechanics to protect your spine.
The 2018 Physical Activity Guidelines recommend 150 minutes of moderate physical activity every week, and more importantly, for bone health they advise strength training for all major muscle groups at least two times a week. Doing many repetitions with light weights is not the way to go. To add sufficient load on the bones, the muscle you are working should fatigue within 12 to 15 repetitions or fewer.
Be safe and smart with your training, and remember: Loading up your workouts will keep your bones going strong for the 3-Day and beyond!
About Dr. Kohrt
Dr. Kohrt is a Professor of Medicine in the Division of Geriatric Medicine at the University of Colorado Anschutz Medical Campus and the Nancy Anschutz Endowed Chair In Women’s Health Research.