Full Length ArticleMid-calf skeletal muscle density and its associations with physical activity, bone health and incident 12-month falls in older adults: The Healthy Ageing Initiative
Introduction
Low lower-limb skeletal muscle density has been associated with higher risk of fractures in older adults [[1], [2], [3], [4], [5]]. Low muscle density is an indicator of higher amounts of intra- and intermuscular adipose tissue (IMAT) and can be assessed at the mid-calf in older adults using peripheral quantitative computed tomography (pQCT) [6]. The relationship of low muscle density with greater risk of fractures is likely to be explained, at least in part, by its associations with poor physical performance [[7], [8], [9], [10]], and also with higher likelihood of falls as reported in retrospective studies [[11], [12], [13]]. However, there is currently a lack of prospective data on the contribution of low muscle density to incident fall risk in older adults.
Another mechanism by which low skeletal muscle density may influence fracture risk in older adults is through its associations with bone health. Lower gluteus maximus and abductor muscle densities are associated with lower hip areal bone mineral density (aBMD) in hip fracture patients [14], and measures of ‘bone qualities’, such as peripheral volumetric BMD (vBMD) and bone geometry [15], also appear to be poorer in those with lower muscle density. Indeed, we recently reported that lower mid-calf muscle density is associated with lower proximal tibial cortical vBMD and area in older adults [16], and high relative lower-leg intra-muscular fat has also been associated with lower tibial bone content and area [17]. The findings of these studies suggest a potential negative localised effect of lower skeletal muscle density on bone health in older adults, but no study has reported associations between muscle density and bone density and architecture at multiple anatomical sites.
Interventions which increase physical activity have been successful in reducing IMAT [18,19], and low self-reported physical activity levels are associated with higher levels of IMAT in multiple patient populations [[20], [21], [22]]. However self-reported estimates of physical activity are subject to recall bias [23]. Accelerometers provide objective estimates of sedentary behaviour and intensity of physical activity but it is currently unclear whether objectively-determined physical activity of different intensities have similar associations with mid-calf skeletal muscle density in older adults.
The primary aim of this analysis of a community-dwelling population of Swedish older adults was to determine the associations of mid-calf skeletal muscle density with 12-month incident falls. The secondary aims were to determine cross-sectional associations of mid-calf muscle density with bone density and architecture at different anatomical sites, and with accelerometer-determined physical activity intensity.
Section snippets
Study design and participants
This was an analysis of the Healthy Ageing Initiative (HAI) cohort study; an ongoing observational study of 70-year-old adults in the Umeå municipality in northern Sweden. The objectives of HAI are to investigate traditional and potentially novel risk factors for cardiovascular disease and injurious falls and fractures in 70-year-old men and women. Two eligibility criteria were applied: 1) Residence in the Umeå municipal area and, 2) 70 years of age at the time of testing. Using contact
Results
Of 3633 participants recruited for this study, 14 and 573 did not complete DXA and pQCT at baseline, respectively. A further 195 participants did not provide complete accelerometer data, and 632 had incomplete falls reports over 12 months. Additionally, inspection of mid-calf muscle density box-plots identified 5 participants as extreme outliers (muscle density ≤ 50 or ≥ 100 mg/cm3) and these participants were also excluded from the analysis. Thus, a total of 2214 participants were included in
Discussion
In this cohort of community-dwelling Swedish older adults, lower mid-calf muscle density was independently associated with higher likelihood for multiple incident falls and appeared to have localised negative effects on bone structure at the tibia. Prospective studies are required to determine whether these associations explain previously observed effects of lower-limb skeletal muscle density on higher risk of fractures in older adults [[1], [2], [3], [4], [5]].
A cross-sectional study of 147
Conclusions
Lower mid-calf muscle density is independently associated with higher likelihood for multiple incident falls over 12 months and may have localised negative effects on bone structure at the tibia. Further studies are required to determine whether these associations persist over the long-term, and potentially contribute to the greater fracture risk previously observed in older adults with low muscle density.
Acknowledgements
The authors would like to thank Healthy Ageing Initiative research personnel Magnus Lindblom, David Lapveteläinen, and Jim Viklund, who were responsible for data collection.
Funding sources
This study was funded by the Swedish Research Council (grant number 2011-2976). DS is supported by a NHMRC RD Wright Biomedical Career Development Fellowship (GNT1123014). LBM is supported by an Australian Postgraduate Award.
Conflicts of interest
None to declare.
References (38)
- et al.
Community-dwelling female fallers have lower muscle density in their lower legs than non-fallers: evidence from the Saskatoon Canadian Multicentre Osteoporosis Study (CaMos) cohort
J. Nutr. Health Aging
(2015) - et al.
Associations of components of sarcopenic obesity with bone health and balance in older adults
Arch. Gerontol. Geriatr.
(2018) - et al.
Fat and muscle indices assessed by pQCT: relationships with physical activity and type 2 diabetes risk
J. Clin. Densitom.
(2012) - et al.
Greater sedentary hours and slower walking speed outside the home predict faster declines in functioning and adverse calf muscle changes in peripheral arterial disease
J. Am. Coll. Cardiol.
(2011) - et al.
In vivo precision of the GE Lunar iDXA densitometer for the measurement of total-body, lumbar spine, and femoral bone mineral density in adults
J. Clin. Densitom.
(2010) - et al.
Reproducibility of peripheral quantitative computed tomography measurements at the radius and tibia in healthy pre- and postmenopausal women
Can. Assoc. Radiol. J.
(2011) - et al.
Structural adaptations to bone loss in aging men and women
Bone
(2006) - et al.
The association between physical activity and reduced body fat lessens with age — results from a cross-sectional study in community-dwelling older adults
Exp. Gerontol.
(2014) - et al.
Computed tomographic measurements of thigh muscle cross-sectional area and attenuation coefficient predict hip fracture: the health, aging, and body composition study
J. Bone Miner. Res.
(2010) - et al.
Hip fractures risk in older men and women associated with DXA-derived measures of thigh subcutaneous fat thickness, cross-sectional muscle area, and muscle density
J. Bone Miner. Res.
(2015)