Elsevier

Bone

Volume 120, March 2019, Pages 446-451
Bone

Full Length Article
Mid-calf skeletal muscle density and its associations with physical activity, bone health and incident 12-month falls in older adults: The Healthy Ageing Initiative

https://doi.org/10.1016/j.bone.2018.12.004Get rights and content

Highlights

  • Lower mid-calf muscle density was associated with increased likelihood for multiple incident falls over 12 months

  • Muscle density was inconsistently associated with bone parameters at the hip, lumbar spine and proximal and distal radius

  • Muscle density was consistently positively associated with tibial bone parameters suggesting local effects on bone health

  • Moderate/vigorous physical activity was positively associated with mid-calf muscle density

Abstract

Background

Lower skeletal muscle density, indicating greater infiltration of adipose tissue into muscles, is associated with higher fracture risk in older adults. We aimed to determine whether mid-calf muscle density is associated with falls risk and bone health in community-dwelling older adults.

Methods

2214 community-dwelling men and women who participated in the Healthy Ageing Initiative (Sweden) study at age 70 were included in this analysis. Mid-calf muscle density (mg/cm3) at the proximal tibia, and volumetric bone mineral density (vBMD) and architecture at the distal and proximal tibia and radius, were assessed by peripheral quantitative computed tomography. Whole-body lean and fat mass, lumbar spine and total hip areal bone mineral density (aBMD) were assessed by dual-energy X-ray absorptiometry. Participants completed seven-day accelerometer measurements of physical activity intensity, and self-reported falls data were collected 6 and 12 months later.

Results

302 (13.5%) participants reported a fall at the 6- or 12-month interview, and 29 (1.3%) reported a fall at both interviews. After adjustment for confounders, each standard deviation decrease in mid-calf muscle density was associated with a trend towards greater likelihood of experiencing a fall (OR 1.13; 95% CI 1.00, 1.29 per SD lower) and significantly greater likelihood of multiple falls (1.61; 1.16, 2.23). Higher muscle density was not associated with total hip aBMD, and was associated with lower lumbar spine aBMD (B = -0.003; 95% CI -0.005, -0.001 per mg/cm3) and higher proximal cortical vBMD (0.74; 0.20, 1.28) at the radius. At the tibia, muscle density was positively associated with distal total and trabecular vBMD, and proximal total and cortical vBMD, cortical thickness, cortical area and stress-strain index (all P < 0.05). Only moderate/vigorous (%) intensity physical activity, not sedentary time or light activity, was associated with higher mid-calf muscle density (0.086; 0.034, 0.138).

Conclusions

Lower mid-calf muscle density is independently associated with higher likelihood for multiple incident falls and appears to have localised negative effects on bone structure in older adults.

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.

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