Shaping America's Future^®

During the past several years we have talked, on this website, about the benefits of physical activity on bone health and bone mineral density (BMD). Bone health and BMD are related to osteogenesis or bone formation.

Our premise on these pages is simple-increased physical activity reduces the risk of bone disease such as osteopenia and osteoporosis plus bone fractures (unless a 250 pound linebacker hits a 150 pound wide receiver).

A report published this past summer in Sports Health has cast further insight and support of the benefits of exercise on the health of peoples' bones. This account provided a broad literature review of what is now known about physical activity and bone health.

The authors concluded there are three areas of significance. Here is their summary.

Area 1: Strain of Activity-The strain magnitude (how hard), the strain rate (repetition) and the strain frequency (repetitive movements) of weight bearing activities are essential in bone health.

• Strain magnitude refers to those activities which put significant strain on the body. This magnitude is caused by "ground reaction forces" derived from weight bearing activities. Picture a gymnast doing a floor routine. Her body strikes the floor with great force as she races across the mat performing various exercises which are part of her routine. Her movements are full (or almost full) body action actions coupled with body support and ground reaction forces. Strain magnitude is also precipitated by very strong muscular contractions as when doing heavy weight training and power sports, e.g. martial arts. Here ground reaction forces may not be as evident, but ballistic moves are.


• Strain rate addresses those activities which require sudden, explosive movements (long and high jumping or dunking a basketball). Rate refers to the speed or power of the body or limb actions. Striking a tennis ball or hitting a baseball forcefully serve as examples. These types of effort tend to be more effective in building healthier bones than strain frequency.


• Strain frequency centers on those activities which have a lower rate (less explosive), but they make up for this deficit with high frequencies of repetitive motions. Prime examples of these less explosive activities are running and possibly mountain biking. The authors pointed out importance of impact differences. "evidence suggests...repetitive, non-weight-bearing activities have minimal benefit to bone...certain modes of exercise or loading, such as cycling or swimming, may not elicit strain effects large enough to promote adaptive osteogenesis." Interestingly, running does produce more bone strength of legs, hips and spine.

Area 2: Type of Training-Training techniques which emphasize interval training techniques (short bursts of intense effort followed by short rests) or plyometrics (a combination of eccentric and concentric muscle contractions, such as jumping off a bench and upon landing jumping back onto another bench) help increase BMD. BMD is the most important factor in preventing fractures and osteoporosis in the aged, and indicates osteogenesis.

Area 3: Age of Training-While building bone density via weight bearing activities is important at all ages, the most critical period for development is during the pre- and early-pubertal period of a young person's life. Obviously, this 9 to 14 year old age group is most affected by weight bearing sports, exercise and activities. Although recent evidence shows that the elderly can benefit from this training as well.

As elementary or middle aged teachers and youth leaders your task is cut out for you. It is not enough to have children simply "stand around" or "run around" if you want to build BMD and bone health. Instead, you need to provide children with a variety of weight bearing activities which put considerable strain on the muscles and bones of their bodies. Some children may resist selected sports, exercise or training. The good news is that there are a host of activities available to make sure sports, exercises and training are weight bearing and vigorous.

Below are a few ideas. Undoubtedly you know others. If you select others make sure the activity is weight bearing (swimming is not, although water polo may be; and bicycling is not unless the majority of time is spent standing on the pedals, as in mountain biking and riding up steep hills).

Weight Bearing Activities to Build Healthy Bones-A to Z
Aerobics, basketball, calisthenics, dancing, exercise balls, fencing, gymnastics, hockey, Indian clubs, jumping rope, kettlebell exercise, lacrosse, marching (as in marching band), Nordic skiing (jumping type), orienteering, pogo sticking, quickstep (as in a fast fox trot), running, soccer, tennis, ultimate Frisbee, volleyball, weight lifting, Xtreme sports (BMX, motor-cross, ski, or skateboarding), yoga (aerobic) and zui-qua (Chinese martial art).

Concluding Thoughts

Keep in mind, however, that we are talking maximum bone development. It is equally true that young (and adults) who are very sedentary will derive bone health benefits from walking and lighter forms of exercise such as gardening and Tai Chi.

Charlie Kuntzleman

References:

Manske, S. L., Lorinca, C. R., Zernicke, R. F. (2009). Bone Health: Part 2, Physical Activity.

Sports Health: A Multidisciplinary Approach 1, 341-346.