Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 https://doi.org/10.1186/s12877-022-02811-3 RESEARCH Open Access The feasibility and reliability of measuring forearm muscle thickness by ultrasound in a geriatric inpatient setting: a cross‑sectional pilot study Delky Meza‑Valderrama1,2,3*, Dolores Sánchez‑ Rodríguez1,4,5, Stany Perkisas6,7, Xavi Duran8, Sophie Bastijns6, Vanesa Dávalos‑Yerovi1,9, Elizabeth Da Costa10 and Ester Marco1,11,12,13 Abstract Background: Given the potential benefits of introducing ultrasound in the clinical assessment of muscle disorders, this study aimed to assess the feasibility and reliability of measuring forearm muscle thickness by ultrasound in a geriatric clinical setting. Methods: Cross-sectional pilot study in 25 participants (12 patients aged ≥ 70 years in an acute geriatric ward and 13 healthy volunteers aged 25–50 years), assessed by three raters. Muscle thickness measurement was estimated as the distance between the subcutaneous adipose tissue-muscle interface and muscle-bone interface of the radius at 30% proximal of the distance between the styloid process and distal insertion of the biceps brachii muscle of the dominant forearm. Examinations were repeated three times by each rater and intra- and inter-rater reliability was calculated. Feasibility analysis included consideration of technological, economic, legal, operational, and scheduling (TELOS) components. Results: Mean muscle-thickness measurement difference between groups was 4.4 mm (95% confidence interval [CI] 2.4 mm to 6.3 mm], p < 0.001). Intra-rater reliability of muscle-thickness assessment was excellent, with intraclass correlation coefficient (ICC) of 0.947 (95%CI 0.902 to 0.974), 0.969 (95%CI 0.942 to 0.985), and 0.950 (95%CI 0.907 to 0.975) for observer A, B, and C, respectively. Inter-rater comparison showed good agreement (ICC of 0.873 [95%CI 0.73 to 0.94]). Four of the 17 TELOS components considered led to specific recommendations to improve the procedure’s feasibility in clinical practice. Conclusion: Our findings suggest that US is a feasible tool to assess the thickness of the forearm muscles with good inter-rater and excellent intra-rater reliability in a sample of hospitalized geriatric patients, making it a promising option for use in clinical practice. Keywords: Muscle ultrasound, Forearm muscle thickness, Intra-rater reliability, Inter-rater reliability, Ultrasound feasibility Background Sarcopenia is a progressive and generalized muscle dis- *Correspondence: dmezaconcepcion@parcdesalutmar.cat ease associated with increased likelihood of adverse 1 Rehabilitation Research Group, Hospital Del Mar Medical Research outcomes [1]. According to the 2018 updated definition Institute (IMIM), Carrer de Llull, 410, 08019 Barcelona, Catalonia, Spain Full list of author information is available at the end of the article from the European Working Group of Sarcopenia on © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​ mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 Page 2 of 9 Older People (EGWSOP2), sarcopenia is suspected in Methods presence of low muscle strength and confirmed by doc- Study design and setting umentation of low muscle quantity or quality [2]. This was a cross-sectional pilot study reported accord- The EWGSOP2 cut-off points to define reduced ing to the Strengthening the Reporting of Observational muscle quantity are based on dual-energy X-ray Studies in Epidemiology (STROBE) recommendations absorptiometry (DEXA) and bio-impedance analy- [19]. The study was performed in the geriatric ward of the sis (BIA) (2). Based on feasibility, accuracy, and low University Center of Geriatrics in Antwerp, Belgium in cost, DEXA has been considered as the reference June 2019. standard for measuring muscle mass in patients with sarcopenia [3]. In light of the latest findings in sarco- Participants penia research, the use of ultrasound (US) –a tech- Volunteers were recruited from two different age groups nique largely known for its diagnostic properties in and settings: 12 patients aged 70 years or older (6 women muscle assessment– has been revisited as a promis- and 6 men, aged 81.8 ± 4.2 years) admitted in an acute ing tool to measure muscle quantity and quality, both geriatric ward who agreed to participate and were able to of which are technically difficult to assess. Studies hold their forearm in the needed position for evaluation, using this portable and inexpensive method that does and 13 healthy adult volunteers (doctors, nurses, and not use ionizing radiation [4] have shown a strong social workers at the study site) younger than 50 years (11 positive correlation with DEXA [5–8], computerized women and 2 men, aged 32.9 ± 8.3 years), without known tomography [9], and magnetic resonance imaging pathologies. Patients with recent surgery or trauma (MRI) results [10–12]. (< 3 months) or neurologic diseases affecting the domi- Muscle US has good intra- and inter-rater reli- nant arm were excluded. ability, as well as test–retest reliability in both older adults and younger populations [13, 14]; neverthe- Variables less, more research is needed, especially in the US measures of muscle size in small muscles [13] and a) To determine muscle thickness of the forearm, each clinical populations [14]. The SARCopenia measure- researcher measured the forearm and marked the ment by UltraSound (SARCUS) project, a European point of transducer placement on the lateral right collaborative partnership, proposes various meas- forearm, 30% proximal of the distance between the urements, including muscle thickness as among the styloid process of the radius and the insertion of most commonly used to evaluate muscle mass in the the biceps brachii muscle into the radial tuberosity upper and lower limbs [4, 15]. Lack of expertise in (Fig. 1A). Using B-mode on the Aplio 300 (Canon US among physicians is one of the critical limitations Medical Systems Europe B.V.), a 5-cm wide 7.5-MHz for its implementation in clinical practice. However, linear transducer with a scanning head coated with published research shows that a brief training course water-soluble transmission gel was used; the probe achieves improvement in point-of-care US image was placed perpendicular to the length of the arm; interpretation skills and confidence [16, 17] and a minimal pressure was maintained between the trans- reliable endpoint can be achieved by the practitioner ducer and the skin (Fig. 1B). The examination was who is inexperienced in more complex musculoskel- performed with the patient seated in a chair without etal US techniques [18]. armrests, with feet fully resting on the floor, and hips The rectus femoris and lateral vastus muscles are the and knees positioned at approximately 90°. The upper most often studied with US in sarcopenia research [4]. limb was resting on a table and positioned as fol- However, some degree of patient collaboration (need to lows: 30-45º shoulder flexion, 45º elbow flexion, mid undress) and observer effort (assistance to position the pronation/supination, 15–30° wrist extension and patient on the examining table or bed, time required 0–15° ulnar deviation. To facilitate standardization for the protocol) is involved. For this reason, our study of positioning, a tennis ball (Wilson Sporting Goods proposed a forearm muscle evaluation protocol with Company, United States of America) was gently held the patient seated naturally and the forearm in a neutral in the hand (Fig. 1C); this position helps to coun- position accessible for US transducer placement. This teract any volitional or nonvolitional contractions pilot study aimed to assess the feasibility of assessing of the musculature to hold the forearm as directed. thickness of the forearm muscles by US and to calculate Once the image was selected, the distance between intra- and inter-rater reliability of these measurements the subcutaneous adipose tissue-muscle interface performed by inexperienced users of the technique in a and the radius muscle-bone interface was measured geriatric inpatient setting. Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 Page 3 of 9 Fig. 1 Measurement of muscle thickness, Legend: A, Muscle thickness was measured at the lateral dominant forearm at 30% proximal of the distance between the styloid process and the distal insertion of the biceps brachii muscle into the radial tuberosity. The black mark indicates where the images should be captured. B, A 5 cm width, 7.5 MHz linear transducer was placed perpendicular to the length of the arm. C, The patient must be seated with the dominant arm resting on a standard table with shoulders flexed to 30-45º, elbow to 135º, and forearm in neutral position (Fig. 2). The mean value of three reproducible meas- Geriatrics with US expertise (2 years working experi- urements (< 15% variability) was used for analysis. ence) provided a 45-min training session; the assess- Each researcher positioned the patient, measured ments were carried out by three researchers (raters and marked the transducer position in the forearm, A, B, and C) with limited or no previous experience captured the image, measured the muscle thickness, in muscle US. and removed any skin marks before the next investi- b) Feasibility of the procedure was assessed with tech- gator entered the examination room. A specialist in nological, economic, legal, operational, and sched- uling (TELOS) components, adapted from previous studies [20]. For the purpose of this study, 17 yes/ no questions (outlined below) with their expected answers were agreed. The components were con- sidered feasible if the answers were those expected; otherwise, actions to resolve barriers were described. Additional feasibility considerations included time spent on the examination, patient discomfort during the procedure, and occurrence of adverse or unex- pected events. Training of evaluators Before starting data collection, a specialist in Geriatrics with US expertise (2 years working experience) provided a 45-min training session designed for physicians with limited or no previous experience in muscle US. The training consisted of three parts: 1) Theory: Content included a) generalities in using Fig. 2 Cross-sectional sonogram of a healthy volunteer, Legend: Forearm muscles assessed: A, Brachioradialis muscle. B, Extensor carpi the US scanner (including adequate grip of the US- radialis longus muscle. C, Extensor carpi radialis brevis muscle. D, transducer, the quantity of gel needed, and pres- Supinator muscle sure management over the area to be evaluated; b) Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 Page 4 of 9 visualization, capture, and measurement of the US version 15 (StataCorp, College Station, Texas, United image; and c) the patient’s position and the meas- States of America) were used for statistical analysis. urement of the anatomical point on the forearm for the evaluation. Results 2) Practical training: The expert measured the fore- All the participants were right-handed. Among the arm muscle thickness by US in a healthy volunteer; patients, no significant differences in muscle thickness of each participant then performed the measurement the dominant forearm were observed between men and in healthy volunteers under expert supervision. women (mean difference 0.06 mm, 95%CI -3.03 to 3.15). 3) Evaluation: At the end of the training, the expert Differences by sex could not be analyzed in the healthy verified that researchers had completed the entire volunteers, as only two men participated. forearm muscle thickness measurement indepen- Twenty-five trios of inter-rater measurements were dently and adequately. Finally, all three researchers evaluated, as described in Table 1. Mean muscle-thick- (raters A, B, and C) carried out the assessments for ness values were calculated for each participant accord- this research. ing to the following formula: [mean A + mean B + mean C]/3. The results were 14.6 ± 2.0 mm in the older patients, and 18.4 ± 2.6 mm in the younger healthy vol- Study size unteers (mean difference 4.4 mm [95%CI 2.4 mm to A sample size of at least 24 observations was deter- 6.3 mm], p < 0.001). Figure 3 shows obtained images in a mined, taking into account a scenario with three patient and a healthy volunteer. raters, 5% significance level, and accepting an alpha The intra-rater agreement analysis showed excellent risk of 0.05 and a beta risk of 0.2 in a two-sided test. results: ICC for raters A, B, and C was 0.947 (95%CI We used the formula provided by Zou [21] using 0.902 to 0.974), 0.969 (95%CI 0.942 to 0.985) and 0.950 the R Package “ICC.Sample.Size” [22], giving a 0.9 (95%CI 0.907 to 0.975), respectively (Table 2). Compar- hypothesized value of the intraclass correlation coef- ison between all three raters showed good inter-rater ficient and a null hypothesis value of 0.75. agreement, with an ICC of 0.873 (95%CI 0.73 to 0.94). However, comparisons between raters had some dispar- ities depending on the pair. Pairs A-B and B-C showed Statistical analysis good agreement, with ICC of 0.89 (95%CI 0.97 to 0.96) Categorical variables are described with absolute values and 0.9 (95%CI 0.78 to 0.96), respectively. When com- and percentages, quantitative variables with mean and paring A and C, the ICC was 0.83 (95%CI 0.43 to 0.94), standard deviation (SD). The assumption of normality with the lower limit of the confidence interval falling of the quantitative variables was checked with normal into the range of poor agreement. probability graphs and the Kolmogorov–Smirnov test Bland and Altman plots (Fig. 4) showed different lev- corrected by the Lilliefors test. Student t-test for inde- els of bias and limits of agreement, ranging from -0.52 pendent samples was used to assess age-related differ- in the B-C comparison to -1.37 in the A-C comparison. ences in muscle-thickness. The intraclass correlation Moreover, pairs of measurement showed no patterns in coefficient (ICC) and its 95% confidence intervals (CI) the distribution of points in the plot area. From a total were calculated to determine both the intra- and inter- of 17 questions considered as relevant to assess feasibil- rater agreement [23]. Intra-rater agreement was based on ity, 4 answers were unknown or not as expected; these a single rating, absolute agreement, 2-way mixed effects- were specifically addressed by describing actions to over- model and inter-rater agreement on a single rating, abso- come potential barriers to implementation (Table 3). lute agreement, 2-way random-effects model [24]. In the Professionals from the Geriatrics and Rehabilitation benchmark scale used to evaluate ICC, values below 0.5 Departments considered that information provided indicate poor agreement and those between 0.5 and 0.75, by muscle US could have clinical and prognostic impli- moderate agreement. We considered good ICC agree- cations. Although no infrastructure investment was ment values as between 0.75 and 0.9 and excellent agree- required, the assessment could be considered time-con- ment above 0.9 [24]. Finally, agreement between raters suming. The researchers in charge of examinations (1 (by pairs of raters) was assessed by Bland–Altman plots; geriatrician and 2 rehabilitation specialists) received a mean of differences or bias and limits of agreement were 45-min theory class followed by a practicum in which 5 calculated [25]. P-values lower than 0.05 were consid- supervised examinations were carried out. ered as statistically significant. Statistical Package for the The inclusion of US assessment in the geriatric ward Social Sciences (SPSS) version 23.0 for Windows (IBM, fulfilled legal requirements. Unlike muscle US of lower Armonk, New York, United States of America) and Stata limbs, for which patients must remove items of clothing, Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 Page 5 of 9 Table 1 The intra- and inter-rater agreement Rater A Rater B Rater C Patients (> 70 y) A1 A2 A3 Mean A B1 B2 B3 Mean B C1 C2 C3 Mean C Mean ABC 1 12.5 12.5 10.6 11.9 11.1 10.8 11.9 11.3 9.2 10.2 9.7 9.7 10.9 2 13.3 14.5 13.6 13.8 14.7 14.9 13.3 14.3 15.3 14.3 15.2 14.9 14.3 3 16.8 17.6 17.1 17.2 18.6 17.2 17.0 17.6 18.2 18.0 17.8 18 17.6 4 11.8 12.5 12.0 12.1 16.3 16.5 16.4 16.4 14.8 15.2 15.3 15.1 14.5 5 12.0 12.6 12.2 12.3 10.5 11.3 11.5 11.1 12.4 13.0 13.5 13.0 12.1 6 13.7 14.1 14.4 14.1 17.4 17.5 17.8 17.6 18.1 18.8 17.0 18.0 16.5 7 14.7 13.2 13.2 13.7 17.3 17.1 16.3 16.9 17.1 17.3 17.3 17.2 15.9 8 12.6 14.0 13.5 13.4 14.9 15.0 13.9 14.6 14.7 14.6 14.6 14.6 14.2 9 10.2 12.2 12.6 11.7 14.3 14.3 13.1 13.9 13.3 14.6 14.3 14.1 13.2 10 14.2 15.0 14.7 14.6 14.1 14.8 13.6 14.2 15.8 14.3 15.8 15.3 14.7 11 10.6 10.1 9.3 10.0 10.8 12.6 12.6 12.0 14.8 18.1 17.9 16.9 13.0 12 12.2 10.7 11.3 11.4 12.0 10.5 12.2 11.6 14.1 10.6 10.9 11.83 11.6 Volunteers (< 50 y) A1 A2 A3 Mean A B1 B2 B3 Mean B C1 C2 C3 Mean C Mean ABC 1 16.5 17.1 16.3 16.6 19.9 18.8 18.4 19.0 24.4 22.4 24.3 23.7 19.8 2 14.2 14.4 17.6 15.4 14.9 16.0 14.8 15.2 14.2 14.8 14.6 14.5 15.1 3 18.2 17.3 17.4 17.6 17.0 16.8 17.3 17.0 21.8 22.2 22.0 22.0 18.9 4 17.5 17.6 19.5 18.2 18.5 18.5 19.7 18.9 19.5 19.5 20.1 19.7 18.9 5 17.4 16.8 16.8 17.0 15.9 16.6 16.4 16.3 16.2 17.8 18.2 17.4 16.9 6 17.7 17.3 16.7 17.2 17.3 16.8 18.4 17.5 18.0 18.0 18.9 18.3 17.7 7 18.5 17.0 18.8 18.1 19.0 18.9 18.9 18.9 19.5 19.4 19.3 19.4 18.8 8 25.3 24.7 23.3 24.4 25.7 25.3 25.8 25.6 25.8 24.7 25.6 25.4 25.1 9 17.1 16.2 15.9 16.4 18.0 18.2 16.3 17.5 22.0 23.1 21.6 22.2 18.7 10 17.6 17.6 17.3 17.5 17.7 17.8 17.7 17.7 17.7 18.0 18.1 17.9 17.7 11 19.9 20.4 19.1 19.8 19.8 21.1 21.1 20.7 17.1 21.5 21.1 19.9 20.1 12 13.9 13.2 13.5 13.5 16.4 15.6 15.5 15.8 15.2 14.4 14.5 14.7 14.7 13 17.6 15.0 16.6 16.4 17.5 18.0 17.9 17.8 16.7 16.6 16.2 16.5 16.9 Legend: Muscle thickness of forearm in older patients and healthy volunteers, measured by three novice raters using ultrasound Fig. 3 Forearm muscle thickness sonogram, Legend: Image obtained in a patient (left) and healthy volunteer (right), showing quantitative differences Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 Page 6 of 9 the mean total time spent in the examination room was measurements, as loss of muscle strength is essential only 12.5 min per assessment; the actual measurement for sarcopenia diagnosis. Our study focused on using was easily performed in less than 10 min per patient. No researchers newly trained in US to assess muscle thick- patients reported discomfort during the examination, ness in hospitalized geriatric patients who could main- and there were no adverse or unexpected effects except tain the protocol’s required sitting position. The good one patient who fell asleep during the procedure. inter-rater and excellent intra-rater reliability data obtained after a 45-min training session demonstrated Discussion that US is an accessible tool for physicians interested in This pilot study showed US technology to be a reli- objective muscle assessment. The US is an inexpensive, able and feasible tool to measure muscle characteris- non-invasive technique that uses no ionizing radiation. tics in older adults. Both quantity and quality are key Modern equipment is portable, making it easy to use in clinical practice. To date, very few research groups have Table 2 Inter- and intra-rater reliability of ultrasound muscle closely examined the usefulness of forearm US in the thickness measurements diagnosis of muscle diseases [26–29]; one of the groups Intraclass correlation coefficient found a close association between US muscle thick- ness and cross-sectional area measured by MRI in the Inter-rater reliability 0.873 (95% CI 0.73 to 0.94) forearm of young and middle-aged individuals [26]. In Intra-rater reliability the present study, a significant forearm muscle thick- -Rater A 0.947 (95% CI 0.902 to 0.974) ness difference was observed between older patients -Rater B 0.969 (95% CI 0.942 to 0.985) and younger healthy volunteers; however, the reasons -Rater C 0.950 (95% CI 0.907 to 0.975) for these differences (age-related loss of muscle mass, Legend: 95% CI 95% confidence interval physical inactivity, medications, comorbidities, etc.) Fig. 4 The Bland and Altman plots show the levels of bias and limits of agreement Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 Page 7 of 9 Table 3 The TELOS components Components Questions to be considered Expected Reported answer Actions to address potential barriers to answer implementation Technology Is the required equipment available in the Yes Yes – institution? Will we need third-party resources? No No – Is staff properly trained to implement the inter‑ Yes No 45-min theory class + practicum (5 supervised vention or will new skills be needed? examinations) Economics Are all the costs well-defined? Yes Yes – Is the intervention expensive? No No – Is the time–cost acceptable? Yes Yes – Legal requirements Does the new intervention conflict with legal No No – requirements?’ Have we ensured that we are following all the Yes Yes – standards of good clinical practice? Operational needs Are all of the tasks properly defined? Yes Yes – Are the involved third parties willing to Yes Yes – participate? Do new teams have to be established? No No – Do we need to reorganize the processes? No No – Will there be staff resistance to the change? No Unknown Discuss the views and questions of all the parties involved Will there be training costs? No Yes Low cost, incorporated into departmental budgeting Scheduling Given our current experience, is the interven‑ Yes Yes – tion realistic? Are there any timescale pressures to be met? No No – Will the intervention deliver meaningful ben‑ Yes Unknown Incorporate a subproject to assess clinical and efits for patients? prognostic implications Legend: Description of the technological, economic, legal, operational, and scheduling (TELOS) components and expected answers supporting the feasibility of introducing muscle ultrasound as a diagnostic procedure offer an interesting and necessary question for future readily accessible than other more studied muscles and research. their measurement shows good reliability, this option A major drawback of US-based measurements is the for screening and diagnosis of muscle disorders could be lack of standardization with respect to aspects such as very useful in clinical assessments, particularly in outpa- preferred muscle group, patient positioning, pretest tient settings where time for examinations is very limited. exercise, dominant vs. non-dominant arm, or relaxed vs. In hospitalized patients who cannot maintain the sitting contracted muscles. In our study, muscle thickness was position, it would be better to assess other muscles (e.g., measured at the proximal lateral forearm, 30% proximal quadriceps in the supine decubitus position). However, of the distance between the styloid process of the radius in the forearm muscle thickness evaluation, the patient and the insertion of the biceps brachii muscle into the need only be seated with a bare forearm held steady in a radial tuberosity, which is the widest and most accessible supported position; this approach optimizes clinical time part of the forearm in a neutral position. and resources in patients who can maintain this posture Other US protocols exist for measuring the forearm for approximately five minutes. musculature. These protocols generally evaluate the ante- Our results suggest that the feasibility of the procedure rior part of the forearm at different levels, have usually is fairly good. Only a short training time was required, sought to demonstrate the maximum handgrip strength although there is a learning curve related to measur- [27], a good correlation between handgrip strength and ing distances and muscle area. Positioning the patient, muscle thickness [28], as an indicator of physical per- handling the probe, and even the force applied by the formance [29], and have shown good intra-rater and examiner during the assessment are aspects that might inter-rater reliability [4, 30–32]. However, there is no influence the accuracy of the measurements. consensus recommending a specific measurement pro- The study of US feasibility in a geriatric setting may tocol for the forearm. Since lower arm muscles are more be considered a strong point of our research, as well as Meza‑Valderrama et al. BMC Geriatrics (2022) 22:137 Page 8 of 9 the use of three observers and a homogeneous popula- Department of Experimental and Health Sciences, Universitat Pompeu Fabra– Doctoral School, Barcelona, Catalonia, Spain. All authors have read and agreed tion of older patients to support our reliability analysis. to the published version of the manuscript. Limitations of the study include the relatively small group of participants, the unknowns that are inherent to the Funding This research has been partially supported by a grant from ‘Secretaria d’Universitats i technique itself (as described above), and the lack of a Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya’. test–retest analysis. Although the lack of a test–retest is a limitation of the design, the reliability obtained through Availability of data and materials The datasets used during the current study are available from the correspond‑ the methodology (image capture and thickness meas- ing author upon reasonable request. ured) achieved the aims of our study. This study aimed to demonstrate how physicians with no previous experience Declarations in muscle assessment by US could perform muscle thick- ness assessment with a high degree of reliability after Ethics approval and consent to participate National and international research ethics guidelines were followed, includ‑ brief training. The methodology included training in four ing the Declaration of Helsinki and current confidentiality law concerning specific areas: (a) general US measurement techniques personal data. Detailed and understandable oral and written information was (correct grip and positioning of the US probe, amount of provided, and informed consent to participate was signed by all participants. This study was approved by the Ethics Committee of the Ziekenhuis Netwerk gel to be used, and attention to the pressure exerted on Antwerpen, Antwerp, Belgium (EC #5226). the tissues); b) anatomical location of the probe place- ment point on the forearm; (c) recognition of the ana- Consent for publication Not applicable. tomical structures in the ultrasound image obtained, and (d) correct measurement of structures in the US image Competing interests captured. The authors declare that they have no competing interests. Author details Conclusion 1 Rehabilitation Research Group, Hospital Del Mar Medical Research Institute Our findings suggest that US is a feasible tool to assess (IMIM), Carrer de Llull, 410, 08019 Barcelona, Catalonia, Spain. 2 Physical Medi‑ cine and Rehabilitation Department, National Institute of Physical Medicine thickness of forearm muscles with good inter-rater and and Rehabilitation (INMFRE), Panama City, Panama. 3 Physical Medicine excellent intra-rater reliability, requiring minimal train- and Rehabilitation Department, Caja de Seguro Social (C.S.S.), Panama City, ing in the technique and limited time during the out- Panama. 4 Geriatrics Department, Brugmann University Hospital, Université Libre de Bruxelles, Brussels, Belgium. 5 WHO Collaborating Centre for Public patient clinical examination. Therefore, it could be a Health Aspects of Musculo‑Skeletal Health and Aging, Division of Public suitable option in Geriatrics and Rehabilitation settings Health, Epidemiology and Health Economics, University of Liège, Liège, Bel‑ for the assessment of muscle characteristics and follow- gium. 6 University Center of Geriatrics, Antwerp University, Leopoldstraat 26, 2000 Antwerp, Belgium. 7 First Line and Interdisciplinary Care Medicine, ELIZA, up of patients with sarcopenia. University of Antwerp, 2650 Edegem, Belgium. 8 Methodological and Biostatis‑ tical Advisory Service. Hospital del Mar Research Institute, Barcelona, Catalonia, Spain. 9 Physical Medicine and Rehabilitation Department, Vall d’Hebron Abbreviations University Hospital, Catalonia, Barcelona, Spain. 10 Physical Medicine and Reha‑ BAMS: The Belgian Ageing Muscle Society; BIA: Bio-Impedance Analysis; CI: bilitation Department, Hospital Del Mar - Hospital de L´Esperança, Parc de Confidence Interval; DEXA: Dual-energy X-ray Absorptiometry; EGWSOP2: Salut Mar, Barcelona, Catalonia, Spain. 11 Geriatric Department, Centre Fòrum- European Working Group of Sarcopenia on Older People 2; ESPEN: The Hospital del Mar, Parc de Salut Mar, Barcelona, Catalonia, Spain. 12 School European Society of Clinical Nutrition and Metabolism; EuGMS: The European of Medicine, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain. 13 Union Geriatric Medicine Society; ICC: Intraclass Correlation Coefficient; School of Medicine, Universitat Internacional de Catalunya, Sant Cugat del MRI: Magnetic Resonance Imaging; SARCUS: SARCopenia measurement by Vallès, Barcelona, Catalonia, Spain. UltrasSound; SD: Standard Deviation; SPSS: Statistical Package for the Social Sciences; STROBE: Strengthening the Reporting of Observational Studies in Received: 27 March 2021 Accepted: 2 February 2022 Epidemiology; TELOS: Technological, Economic, Legal, Operational, and Sched‑ uling components; US: Ultrasound. Acknowledgements The authors appreciate English language review by Elaine M. Lilly, PhD. This References work was conducted within the framework of the Doctorate in Health Sci‑ 1. Beaudart C, Zaaria M, Pasleau F, Reginster JY, Bruyère O. Health Outcomes ences from Universitat Pompeu Fabra in Barcelona. of Sarcopenia: A Systematic Review and Meta-Analysis. PLoS One. 2017;12(1):e0169548. Authors’ contributions 2. Cruz-Jentoft AJ, Bahat G, Bauer J, Boirie Y, Bruyère O, Cederholm T, et al. EM and DMV designed the study and were involved in data analysis, data Sarcopenia: revised European consensus on definition and diagnosis. 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