According to the Brazilian Institute of Geography and Statistics - IBGE, in 2022, approximately 15% of the Brazilian population was aged ≥ 60 years. Estimates suggest that by 2060, this proportion will be around 32%. 

The increase in life expectancy reflects the improvement in health conditions, mainly due to technological and medical advances, that contribute to the demographic transition, characterized by a reduction in fertility and infant mortality rates.

It is known that changes in body composition are common in the older adult population because several factors associated with the aging process can contribute to changes in fat and muscles, such as a reduction in strength and muscle mass and an increase and redistribution of adipose tissue. These changes can contribute to the development of diseases or syndromes such as sarcopenia and frailty, which are related to adverse health outcomes such as falls, fractures, hospitalization, and morbidity and mortality.

Therefore, it is crucial to assess muscle strength and mass in older adults to prevent, diagnose, and even treat conditions related to nutritional status and body composition that can harm their health.

Muscle strength can be assessed by some quick, easy, and low-cost methods, such as the sit and stand test and the handgrip strength test (HGS), which are easily implemented in clinical practice.

Although there are several methods for estimating muscle mass, the gold standard methods such as computerized tomography and magnetic resonance imaging are expensive, more technically complex, and are not portable. Dual-energy X-ray absorptiometry (DXA), despite being recommended as a reference method rather than the gold standard, is also expensive and not portable. Equipment that is less expensive and portable, such as some electrical impedances, for example,  have by several limitations when used in older adults, as the results depend on following a strict protocol before the test, and other factors such as temperature and the equations used can also influence the results of muscle mass estimation using electrical impedance. The European Working Group on Sarcopenia in Older People recommends assessing calf circumference (CC) when there are no other methods available, but it is known that CC is influenced by some factors such as edema and adiposity. Considering the above, there is a need for easy, fast, and accurate equipment when compared to gold standard and/or reference methods for estimating muscle mass in older adults in clinical practice. Ultrasound images are emerged in the last few years as a potential alternative to traditional methods, especially portable devices.

Therefore, our study aimed to evaluate the association between muscle thickness (MT) measurements assessed by portable A-mode ultrasound and muscle quantity by DXA in older adults.

In our study, we assessed muscle strength through HGS using a calibrated hand-held dynamometer. We assessed appendicular muscle mass (ALM) and muscle mass (MM) using DXA and MT (biceps, triceps, anterior thigh, and calf) using a portable A-mode ultrasound (BodyMetrix BX-2000) according to the equipment instructions.

We found a moderate correlation between the MM of the arms and the sum of the MT of the biceps and triceps. There was no correlation between the MM of the legs and the sum of the MT of the thigh and calf. We found a strong correlation between ALM and HGS, as well as a weak correlation between MT sum biceps and triceps and HGS.

The sum of  MT measured in the biceps, triceps, thigh, and calf by ultrasound showed no significant association with ALM measured by DXA when controlling for variables such as sex and age. However, MT of the biceps and triceps (MT of the arms) showed a significant association with MM of the arms. It is worth remembering that ALM is the sum of the MM of the arms and legs. ALM is recommended by EWGSOP2 to assess MM in older adults for the diagnosis of sarcopenia.

Our results showed that portable A-mode ultrasound may not be suitable for estimating the sum of arm and leg MM, but may be suitable for estimating arm MM in healthy older adults. More research is needed, as our study was carried out with a non-representative sample of Brazilian older adults.

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The study was supported by the São Paulo Research Foundation (FAPESP) [Finance
Code 2021/01304-0 and 2020/00944-2], by Coordination for the Improvement of
Higher Education Personnel—Brazil (Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior—CAPES), Finance Code 001, and, the Lemann Center for Brazilian
Studies.