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Boning up on skeletal exercise science: Being physically active when young has important implications for the prevention of osteoporosis in old age

11/11/2009
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At a recent Tucker Table, colleagues in the School of Kinesiology outlined some old pervasive myths and new research paradigms pertaining to bone health. Bone health has typically been constructed as a “female issue” when linked with the female athlete triad, ammenorea, menstrual health, and/or osteoporosis. What gets erased when it is framed as a female issue is that bone health is an important issue for everyone.


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Moira Petit, PhD, Associate Professor, School of Kinesiology,

University of Minnesota

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Julie Hughes, MA, doctoral student, School of Kinesiology,

University of Minnesota

Exercise is a key determinant of a strong skeleton. When we exercise, our bones get stronger. On the other hand, when we park it on the couch and watch 24 straight hours of 24, we tend to lose bone. This isn’t a good thing given that a strong skeleton offsets the risk of bone fragility and fracture. While it has been known for some time that bones become stronger in response to exercise in youth, bone experts have debated whether these benefits will persist into old age when osteoporosis is most prevalent.

The concept that exercise in youth is important for bone health comes from several important studies1. One study demonstrated that as much as 26% of bone mineral is accrued in a two-year period during puberty2. This indicates that youth is a critical time to assure the attainment of a strong adult skeleton. Moreover, several human and animal studies show that bone responds more favorably to exercise during youth than in adulthood. For example, a study of female racquet-sport players demonstrated that if the players began playing at or before menarche rather than after it, there would be a much greater benefit in terms of bone mineral content between the dominant and non-dominant arm bones3. Studies like these tell us that youth is an important time to be physically active to build a strong skeleton, but evidence has been lacking as to whether these benefits will persist into old age. As you can imagine, a research study that randomized young children to be physically active or to be sedentary for their entire lives would not only be impractical but also unethical due to what we know about the benefits of exercise.

A recent animal study4 provides some much-needed evidence for this debate. Warden and colleagues from Indiana University explored the effects of exercise in youth on bone strength in old age…in rats. The researchers exercised the right arm bones of young rats 3 days per week for 7 weeks when the rats were young. The left arm bones of the rats were not exercised and served as controls for comparison. The exercise was then discontinued for the rest of the rats’ lives. In old age, the exercised arms of the rats had 24% greater bone strength than the unexercised arm bones—demonstrating that, despite cessation of exercise before adulthood, exercise during youth had skeletal benefits that lasted into old age.

What does this mean for us? Well, since we aren’t rats (unless you are reading this, and your name is Splinter), it is fair to ask if these findings apply to us. The best way we can answer this question is to say that, theoretically, our bones should adapt to exercise in a similar manner to those of the rats in the reviewed study. The benefits that increased the bone strength of the rats were structural. Basically, the long bones increased in diameter, which made them stronger. This phenomenon also occurs in human bones in response to increased exercise. So what should we do about this evidence? Quite simply, yet importantly, these and related findings suggest that it is important to get kids to be physically active now in order to prevent bone fragility when they are older and at greatest risk for osteoporotic fracture.

Look for a future blog about the relationship between bone and menstrual health!

Works Cited

1. Petit MA MH, McKay HA, Lloyd TA. Bone Acquisition in Adolescence. In: R Marcus DF, D Nelson, C Rosen, ed. Osteoporosis. 3 ed. New York: Academic Press; 2007.

2. Bailey DA. The Saskatchewan Pediatric Bone Mineral Accrual Study: Bone mineral acquisition during the growing years. Int J Sports Med. 1997;18:S191-S194.

3. Kannus P, Haapasalo H, Sankelo M, et al. Effect of starting age of physical activity on bone mass in the dominant arm of tennis and squash players. Ann Intern Med. 1995;123:27-31.

4. Warden SJ CA, Nelson IR, Turner CH. Exercise when young provides lifelong benefits to bone structure and strength. JBMR. 2007;22(2):251-259.

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