6533b827fe1ef96bd1285b22

RESEARCH PRODUCT

Estimating Lower Limb Skeletal Loading

subject

description

Osteoporosis, accidents and subsequent bone fractures cause suffering on an individual level, as well as an economical burden to the society (Ortiz-Luna et al., 2009; Stevens & Olson, 2000). It has been estimated that, in Finland alone, between 30,000 to 40,000 osteoporosis-related fractures occur annually and that 400,000 Finnish people have osteoporosis (Duodecim, 2008). There are a few potential ways of preventing bone fracture, i.e. strengthening bones and/or preventing falls (Ortiz-Luna et al., 2009; Stevens & Olson, 2000). In order to withstand prevalent loading without breaking; while remaining relatively light in weight to allow for locomotion, bones have the ability to adapt their structure to functional loading (Frost, 2000; 2003; Sievanen, 2005). It has been demonstrated that physical activity affects the weight bearing skeleton more than the non-weight bearing one (Mikkola et al., 2008), and it may therefore be argued that, the skeleton is loaded mainly by locomotory actions that impart strains on bones. Bones are loaded in daily activities by muscles accelerating and decelerating body segments and resisting the pull of gravity (Burr et al., 1996). Since falling is the single most significant bone fracture risk factor (Jarvinen et al., 2008) and up to 90% of fractures are caused by falls (Cummings & Melton, 2002; Stevens & Olson, 2000; Wagner et al., 2009), exercise can be viewed as a potential intervention for fracture prevention. Exercise seemingly has a potential of both reducing the fall rate and also increasing bone strength. In agreement, exercise interventions have been shown to successfully decrease the fall rate (Kemmler et al., 2010; Korpelainen et al., 2006), to strengthen the bones and to decrease the fracture rate (Korpelainen et al., 2006; Sinaki et al., 2002). It is quite obvious, that in some cases even the strongest bone could not withstand the loading associated with falling. Therefore, it is reasonable to question whether strengthening bones makes a significant contribution in preventing fractures. A prospective study has shown that people with higher calcaneal bone mineral density had lower fracture rate even while the fall rates between the groups were relatively similar (Cheng et al., 1997). The differences between the groups in bone mineral density were relatively large (~10%). In agreement, prospective studies have shown that increasing the amount of bone mineral with drugs by about 10% is effective in decreasing fracture rates (Cummings et al., 2009). On the other hand, the increments in bone mineral amount associated with year long exercise interventions are relatively modest, i.e. in the order of 1 2% (Nikander et al., 2010). There are examples of fractures for which this kind of relatively modest bone strength increase does play an important role. One of the most convincing examples is vertebral fractures. It has been shown in a prospective study that vertebral bone mineral density (represents 11