Exercise is Medicine

Jade Teta ND, CSCS, and Keoni Teta, ND, LAc, CSCS

Building Bone and Plyometrics

Regular physical activity has been shown to positively affect bone density.^1,2 Exercise, compared with drug or nutritional approaches, is especially suited to treat diseases of bone loss because it improves bone density, geometry, and “neuromuscular competency.” Exercise is a holistic intervention that not only reduces risk of fracture if one does fall, but also makes one far less likely to fall in the first place.^2,3

The Mechanostat Theory

The mechanostat theory states that bone has set points of minimum effective strain (MES) which determine whether bone will be gained or lost.^5,6 If forces on bone increase more than what the bone is accustomed to (i.e., relative MES), mineral flux into bone increases. This, along with compensatory structural changes, helps bone become competent enough to deal with increased functional demand. Likewise, if demands on bone decrease and fall below the MES threshold, bone metabolism changes result in weaker bone.⁷ The latter scenario often prevails in age and illness and can happen very quickly. During periods of immobilization, bone mineral density (BMD) can decline as fast as 1% per month.^8,9

Holistic Bone Health

Dual energy X-ray absorptiometry (DEXA) scan is the most popular way to assess bone strength but is often misleading. Measuring bone density alone does not provide an adequate measure of holistic bone strength and health.⁴ To determine the full impact of exercise, all bone parameters should be assessed. To properly ascertain bone strength, cortical thickness and bone diameter are equally important to bone mass. Cortical bone, the outer portion, is responsible for 80% of bone strength. Thicker bones are also stronger bones. By measuring density, cortical bone, and thickness, we get a much more accurate picture of how much force a bone can handle. Effective exercise should address all these areas. In addition, bone-building exercise should be aimed at developing functional parameters that prevent a fall in the first place. This means that exercise modalities which build strength, flexibility, balance, and reaction speed cannot be ignored.

What Defines Functional Bone-Building Exercise?

Functional exercise is a term that describes a system of exercise that targets mainly the muscles of the core (the abdomen and lower back) and focuses on balance training, mimicking the activities of daily living. Before functional exercises such as balance training are employed, however, it may be more important to develop a base of strength and power. Weight-training exercises build both these parameters and also improve flexibility.¹⁰ A stronger, more flexible leg is automatically a more stable leg.

High-intensity and -velocity training may be able to safely mimic the effects of heavy weight training using less resistance. This type of exercise builds power – the combination of strength and speed. It is interesting to note that a patient in danger of falling and breaking a hip does not fall in slow motion, but instead must react with lightning muscular speed and have adequate bone strength to keep from injury. This is what power training accomplishes. While many physicians may shy away from prescribing power training to their older clients, studies have shown it to be more effective than standard resistance training exercise.

Stengal et al., in the Journal of Applied Physiology (July 2005), compared standard weight training with power training in postmenopausal women.¹¹ In the weight-training group, movements were kept slow, while in the power group, exercises were performed much faster. All other exercise parameters were left the same. At the conclusion of the study, the power group showed a statistically significant gain in bone based on DEXA. A small amount of bone was lost in the strength-training group, although these changes did not reach statistical significance. The interesting thing about this analysis was the idea that even lighter weights lifted with “fast intention” can create an effect.

In addition to heavy weight training and power training, jumping exercises show promise as a bone-building aid. Dr. Eric Strong of Brigham Young University did his PhD dissertation on the effect of jumping movements on bone.¹² In his study, three groups of women were tracked for 16 weeks. One was a control group who simply stretched every day, while the two other groups engaged in jump training. The jumpers were instructed to jump as high as they could, taking 30 seconds between each jump. One group did 20 jumps and the other 10. Each group did this jumping protocol twice per day. At the end of the study, the jumping groups saw increased bone density, with the group completing 20 jumps surpassing the 10-jump group. Slight losses in bone were seen in the stretching group. Other studies, including one published in the journal Bone, echo Strong’s findings and point to more “holistic” bone effects.³ The researchers in this study followed women for 1 year and measured their total number and intensity of impacts. At the end of the study, women who had the greatest number and the highest intensity of impacts had the most favorable changes in all parameters on bone health, including bone mass, bone geography, cortical thickness, and bone diameter.

Prescribing Exercise

We use a three-step progression with our bone-building patients. The first step is foot drops: the client rises onto the toes and then lets the body fall back down under the force of gravity so that the heel strikes the ground. Because the body does not rise so high into the air, the impact forces are minimized; however, to the untrained physiology, this impact can have an effect and prepare the body for greater forces later. The next progression has the patient step up and off a high bench. This creates a little more impact than the foot drops. We like this exercise because it has the added benefit of working on balance, coordination, and strength, as well as providing repeated impacts. Once a sufficient base of strength has been built and these other impact exercises have been used, you can progress to true plyometric (jumping) training. To start, have the client jump only slightly into the air. As time goes on, coach her on getting higher and higher and generating more force. Keep in mind the proper form for a squat jump. The feet should land with the toes pointed straight out in front of the patient. The knees should land slightly bent and glutes should be pushed back as if the client were going to sit in a chair. The reaction forces of jumping are between 2 and 6 times the body weight, so this may be a little much for more obese patients.

When done correctly and in combination with other bone-building free-weight exercises, these exercise can provide a useful adjunct to other treatments and work through mechanisms that pharmaceuticals and nutritional interventions neglect. Don’t be surprised if you begin to see changes in patient’s DEXA scans. You can also be confident that you are building all the other parameters of bone strength as well. Smart bone training combines the best of heavy resistance exercises, fast power training, and impact exercises.

Final Thoughts

Quality interventions for building bone, whether pharmaceutical or natural, are in short supply in medicine. Load-bearing exercise is an effective and safe modality that can reach the intensity levels necessary to improve multiple parameters of bone health. It appears that intensity, velocity of movement, and jumping exercises can all provide benefit in this regard.

Notes

1. Borer et al. Physical activity in the prevention and amelioration of osteoporosis in women: interaction of mechanical, hormonal and dietary factors. Sports Med. 2005;35:779–830.

2. Kohrt et al. Physical activity and bone health. Med Sci Sports Exerc. 2004;36:1985–1996.

3. Vainionpaa et al. Effect of impact exercise and its intensity on bone geometry at weight-bearing tibia and femur. Bone. 2007;40:604–611.

4. Watts et al. Fundamentals and pitfalls of bone densitometry using dual-energy X-ray absorptiometry (DXA). Osteoporos Int. 2004;15:847–854.

5. Frost et al. The mechanostat: a proposed pathogenic mechanism of osteoporosis and the bone mass effects of mechanical and non-mechanical agents. J Bone Miner Res. 1987;2:73–85.

6. Skerry et al. One mechanostat or many? Modifications of the site-specific response of bone to mechanical loading by nature and nurture. J Musculoskelet Neuron Interact. 2006;6:122–127.

7. Lanyon et al. Using functional loading to influence bone mass and architecture: objectives, mechanisms, and relationship with estrogen of the mechanically adaptive process in bone. Bone. 1996;18:S37–S43.

8. Shackelford et al. Resistance exercise as a countermeasure to disuse-induced bone loss. J Appl Physiol. 2004;97:119–129.

9. LeBlanc et al. Bone mineral and lean tissue loss after long duration space flight. J Musculoskelet Neuron Interact. 2000;1:157–160.

10. Monteiro et al. Influence of strength training on adult women’s flexibility. J Strength Cond Res. 2008;22(3):672–677.

11. Stengal et al. Power training is more effective than strength training for maintaining bone mineral density in postmenopausal women. J Appl Physiol. 2005;99:181–188.

12. Strong E. Effects of different jumping programs on hip and spine bone mineral density in premenopausal women [dissertation]. Provo, UT: Brigham Young University; 2004.

13. Bailey et al. Exercise for optimising peak bone mass in women. Proc Nutr Soc. 2008;67:9–18.