Muscle Strength and it’s Relationship to Bone Health

stretching with a resistance band

Contributed by Sarah L West, PhD, Post-doctoral Research Fellow, The Hospital for Sick Children and the Faculty of Kinesiology and Physical Education, Human Physiology Research Unit, University of Toronto

As outlined by Ms. Fiona Callender in her previous research contribution, as we age we all experience loss in muscle function and size.  But another important change that happens with aging, and something that should not be ignored, is a loss in bone health and strength.  Bone health is extremely important from an exercise perspective; your muscles attach to your bones, which allow you to move.  As well, breaking a bone (a fracture) can be very debilitating to your health and dramatically reduce your ability to participate in physical activity.  Our bones are actually their strongest at about the age of 18-20 years old; this is referred to as your “peak bone mass”.  However, after age 20 our bone mass (the quantity of bone you have) begins to decline.  So our bones are something we should be thinking about early on in life, as well as while we age!

Osteoporosis is a disease characterized by low bone mass, and having osteoporosis increases someone’s risk of developing a fracture. Osteoporosis is very common, and although many believe it only affects women, it actually affects men as well. Worldwide it is estimated that 1 in 3 women and 1 in 5 men over the age of 50 will break a bone related to having osteoporosis (International Osteoporosis Foundation, 2014).  This is a big problem, because bone fractures are associated with long hospital stays, physical discomfort, disability, and even death.

Exercise is well known to be beneficial for bone health, but is there any association between muscle fiber type, and bone health with aging?  A recent article (2013) by Terracciano and colleagues began to address this question. They examined 15 women with osteoporosis, aged 60-85 years old (they also looked women with arthritis, however we will focus on the results in those with osteoporosis). These women had muscle biopsies of the upper leg, and the muscle fibers were assessed for size, quantity, and function. The women also had their bone health measured by a very common imaging method (called dual energy x-ray absorptiometry) (Terracciano et al., 2013).

What the authors of this article found is very interesting. In women with osteoporosis, there was a preferential decrease in fast twitch muscle fiber size (rather than slow twitch muscle).  As well, this reduction in fast twitch muscle fiber size was correlated with their bone health- those who had more fast twitch muscle fiber loss had worse bone mass (specifically at the hip) (Terracciano et al., 2013). This suggests that there is a connection with fast twitch muscle fiber size and maintaining bone health!

In the research that Ms. Callender reviewed, older trained sprinters maintained the size and strength of their muscle fibers compared to untrained individuals. When you consider the findings of the research Ms. Callender reviewed combined with those from Terraccioano et al., sprint training may help to not only maintain muscle fiber size, but may also result in benefits to bone health in those who have osteoporosis!

While only speculation at this point, taken together the research provides convincing evidence that future studies should investigate the role of fast twitch muscle fiber training on bone health and fracture risk in aging adults. Terraccioano et al. also suggest that exercise could be useful in preventing both muscle and bone loss.  In conclusion, it is important to consider that exercise training targeting fast twitch muscle fibers is not only important from a muscle function perspective, but that it may be important to bone as well!

Sources:  

International Osteoporosis Foundation (2014). Facts and statistics. 2014, from http://www.iofbonehealth.org/facts-statistics – category-14

Terracciano, C., Celi, M., Lecce, D., Baldi, J., Rastelli, E., Lena, E., Mass R., and Tarantino, U. (2013). Differential features of muscle fiber atrophy in osteoporosis and osteoarthritis. Osteoporos Int, 24(3), 1095-1100.

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