Sarcopenia is a condition characterized by the progressive loss of muscle mass and strength associated with aging (Rosenberg, 1997). However, the decline in muscle strength occurs at a faster rate than the reduction in muscle mass in older individuals (Goodpaster et al., 2006). In 2016, sarcopenia was officially recognized as a disease and included in the International Classification of Diseases (ICD) under the ICD-10-CM code M62.84 (Anker et al., 2016).

This condition is associated with multiple adverse health outcomes, including disability and functional decline (Janssen et al., 2002), an increased risk of falls (Scott et al., 2014), and higher mortality rates (Westbury et al., 2023). These clinical consequences lead to a significant increase in healthcare costs. In 2014, individuals diagnosed with sarcopenia generated an additional annual healthcare expenditure of approximately $2,315.7 per person compared to those without the condition (Goates et al., 2019).

The most commonly used diagnostic algorithms for sarcopenia have been developed by the European Working Group on Sarcopenia in Older People (EWGSOP) (Cruz-Jentoft et al., 2019), the Asian Working Group for Sarcopenia (AWGS) (Chen et al., 2020), and the Foundation for the National Institutes of Health (FNIH) (Studenski et al., 2014). Additionally, other diagnostic approaches have been proposed by the International Working Group on Sarcopenia (IWGS) (Fielding et al., 2011) and the Sarcopenia Definitions and Outcomes Consortium (SDOC) (Bhasin et al., 2020). Each of these algorithms incorporates different functional tests, leading to variations in diagnostic procedures, as well as the need for specific equipment and time for implementation.

One of the main reasons for discrepancies in sarcopenia prevalence is the heterogeneity in diagnostic tests, established cutoff points, and the equipment used to depend on the applied algorithm (Pedauyé-Rueda et al., 2024). In scientific literature, sarcopenia prevalence varies widely, ranging from 9.9% to 40.4%, with an increasing trend as age progresses (Chang et al., 2020). These differences can be attributed to the use of different diagnostic algorithms and variability in tests assessing muscle strength, such as the 5-Sit-To-Stand Test (5-STST) and handgrip dynamometry (Celis-Morales et al., 2018; Cofré-Bolados et al., 2021). Two studies using the EWGSOP algorithm reported different prevalence rates depending on the test used to assess muscle strength: in one study, prevalence was 3.1% when applying the 5-STST (Johansson et al., 2020), whereas another study found a 3% higher prevalence when using handgrip dynamometry (Yee et al., 2021).

Muscle power has been identified as the most relevant predictor of functional limitations in older adults (Martinikorena et al., 2016). Various studies have employed equations incorporating variables such as leg length, chair height, and execution time to estimate muscle power. However, these methods have not been validated against reference instruments (Takai et al., 2009; Yanagawa et al., 2015). Additionally, equations have been developed to estimate power as a means of providing cost-effective and easily applicable tools for assessing sarcopenia and functional capacity in geriatric populations. Nevertheless, these equations have not yet replaced previously validated methods (Alcazar et al., 2018b).

Other methodologies for assessing muscle strength include the One-Repetition Maximum (1RM) test, the Countermovement Jump (CMJ), and the maximum number of repetitions with a fixed load test. However, their application in older adults is limited due to their high physical demands, induced fatigue, and potential physiological alterations (Rodrigues et al., 2024). Consequently, these methods have primarily been restricted to sports performance assessment (Alcazar et al., 2018a).

Current sarcopenia case-finding and diagnostic pathways, including the European Working Group on Sarcopenia in Older People 2 (EWGSOP2) algorithm, rely on functional tests such as handgrip strength, the 5-times sit-to-stand test, gait speed and the Timed Up and Go. However, in real-world geriatric settings these assessments may be limited by pain, balance impairment, mobility restrictions and fatigue, and they can be impractical when space, time or equipment are constrained. Moreover, several widely used outcomes depend on manual timing or indirect calculations, which may reduce precision and comparability across settings. Although muscle power and movement velocity are closely related to functional limitation in older adults, they are rarely quantified directly in routine sarcopenia assessment. This highlights an unmet need for a brief, low-burden, objective and instrumented test that can complement existing algorithms and provide an operational alternative when standard tests are not feasible or are contraindicated. To address this gap, we developed the Sarcopenia Optoelectronic Chair-Rise Velocity Test (SARC-T), which quantifies mean propulsive velocity during a chair-rise task using a validated optoelectronic encoder.

To support implementation in clinical and research settings, the measurement properties of SARC-T should be evaluated using an accepted framework for outcome measurement instruments. The COSMIN initiative provides consensus-based terminology and standards to assess key measurement properties (e.g., validity) across outcome measurement instruments, including performance-based tests. Accordingly, and given that SARC-T is not a patient-reported outcome measure, we focused on validity-related measurement properties that are applicable to performance-based instruments (Mokkink et al., 2010).

In this context, the primary aim of this cross-sectional study was to evaluate construct validity (hypotheses testing) of SARC-T in older adults by examining a priori expected correlations between SARC-T mean propulsive velocity and EWGSOP2-recommended functional tests used to estimate probable sarcopenia and severity. A secondary aim was to evaluate known-groups validity by testing whether SARC-T discriminates between older adults classified with sarcopenia and age- and sex-matched non-sarcopenic controls. As an additional objective related to feasibility and safety, we characterised the physiological load of the procedure by recording heart rate, blood pressure, and oxygen saturation before and after testing.

A total of 38 older adults diagnosed with sarcopenia according to the EWGSOP2 algorithm were recruited and compared with 38 healthy subjects. The descriptive characteristics of the participants are presented in Table 1.

Construct validity was evaluated according to COSMIN recommendations by testing a priori hypotheses regarding the expected direction and magnitude of the associations between SARC-T mean propulsive velocity and EWGSOP2-recommended functional tests. As shown in Table 2, higher SARC-T velocity was associated with better functional performance in both groups, showing inverse correlations with time-based tests (5-times sit-to-stand, gait speed test time and Timed Up and Go) and positive correlations with handgrip strength. All four a priori hypotheses were confirmed in both the control and sarcopenia groups (Table 2), supporting construct validity of SARC-T. Correlation network graphs are provided as supplementary visualisations in Supplementary Material S1 (Supplementary Figures S1, S2).

As shown in Table 3, SARC-T mean propulsive velocity was significantly lower in the sarcopenia group than in age- and sex-matched controls (p < 0.001), with a large between-group difference (Hedges’ g = 0.88, 95% CI 0.41–1.35). Consistent between-group differences were also observed in EWGSOP2-recommended functional tests, with the sarcopenia group showing slower performance in time-based tests (Timed Up and Go, gait speed test time, and 5-times sit-to-stand) and lower handgrip strength. Effect sizes ranged from moderate (TUG and gait speed test time) to very large (5-times sit-to-stand; g = −1.73, 95% CI −2.26 to −1.20), further supporting the discriminative capacity (known-groups validity) of SARC-T.

Physiological variables measured before and immediately after SARC-T showed no evidence of meaningful between-group differences in pre–post change scores (Table 4). Specifically, the changes in oxygen saturation, heart rate, systolic blood pressure and diastolic blood pressure were comparable between the control and sarcopenia groups (all p > 0.05). Physiological responses for the remaining functional tests are provided in Supplementary Material S2 (Supplementary Table S1).

As shown in Table 5, baseline and post-test values of SpO₂, heart rate and blood pressure were comparable across SARC-T and the other functional tests (TUG, gait speed, 5-STST and handgrip) within the sarcopenia group. No statistically significant differences were observed across tests for any physiological variable at baseline or immediately after testing (all p > 0.05). Importantly, SARC-T did not elicit a greater or more concerning physiological response than the assessments routinely used in sarcopenia evaluation, with no indication of disproportionate desaturation, tachycardia or blood pressure elevations when compared with the other tests. The physiological response across the different functional tests in the control group is presented in Supplementary Material S3 (Supplementary Table S2).

The aim of this study was to evaluate the relationship between a movement speed–based physical test (SARC-T) and the functional tests included in the EWGSOP2 diagnostic algorithm, which are used to estimate the probability of sarcopenia and/or its severity.

In line with COSMIN recommendations for performance-based outcome measurement instruments, we evaluated validity-related measurement properties of SARC-T using construct validity through hypothesis testing and known-groups validity. Analysis of the tests included in the diagnostic algorithm showed statistically significant differences between participants with sarcopenia and the control group in all evaluations conducted. In particular, SARC-T revealed a significant reduction in mean propulsive velocity in individuals with sarcopenia compared to matched controls, supporting its ability to discriminate between groups. A plausible interpretation is that SARC-T captures a velocity-related component of the sit-to-stand task that may be linked to neuromuscular function and power generation, which can be affected in sarcopenia. Therefore, mean propulsive velocity could reflect aspects of functional impairment that are not fully captured by completion time alone, and may provide complementary information when evaluating physical performance.

Regarding construct validity, SARC-T was significantly associated with all EWGSOP2-recommended functional tests examined, and the observed direction and magnitude of the associations were consistent with our a priori hypotheses. In the sarcopenia group, correlations ranged from moderate to strong across outcomes, with particularly strong associations with handgrip strength, 5-times sit-to-stand, and Timed Up and Go, while the association with gait speed test time was moderate. Similarly, in the control group, correlations ranged from moderate to strong in all cases. Overall, all a priori hypotheses were confirmed, supporting construct validity of SARC-T. The stronger associations observed in the sarcopenia group may indicate a wider range of functional impairment (greater variability), which can amplify correlations between related performance constructs. Alternatively, movement velocity may become more ‘limiting’ as neuromuscular reserve decreases, strengthening the coupling between SARC-T and established functional outcomes. This should be examined in larger samples and across severity strata.

The 5-STST is widely used to assess lower limb strength and predict fall risk in older adults (Zou et al., 2022). Additionally, it has been used to estimate power generated during the maneuver of standing up from a seated position. Previous studies have established minimum power threshold values required to complete the test, showing that reduced power levels are associated with frailty in the geriatric population (Alcazar et al., 2021; Baltasar-Fernandez et al., 2021). The methodology used in these studies is based on measuring the time required to complete the test, followed by applying an equation that integrates variables such as execution time, subject height, and chair height to calculate movement power. However, this approach has methodological limitations, as variability in chair height and the imprecision of manual timing with a stopwatch may compromise the reliability and comparability of results.

Although the 5-STST is adapted for the geriatric population, many older adults present comorbidities that may complicate, alter results, or even prevent the execution of physical tests included in sarcopenia diagnostic algorithms. These conditions include Parkinson’s disease (Ponsoni et al., 2023), renal failure (Duarte et al., 2024), cardiovascular diseases, type II diabetes, dementia, and respiratory diseases (Pacifico et al., 2020; Zhang et al., 2021), all of which can affect mobility and functional capacity and, consequently, the execution and accuracy of these assessments. Additionally, in individuals with chronic heart failure, the 5-STST induced a significant increase in heart rate and perceived exertion (Tanriverdi et al., 2023). In patients with pulmonary disease and cancer, this test has also been associated with oxygen desaturation and increased fatigue in individuals with sarcopenia (Tremblay Labrecque et al., 2020; Martínez-Herrera et al., 2022).

Furthermore, a strong correlation has been reported between maximum acceleration, measured via accelerometry, and performance in the 5-STST in the geriatric population (Tateoka et al., 2023). It has also been shown that the speed at which an older adult rises from a chair may be a more informative parameter for assessing muscle function than the total time required to complete a repeated sit-to-stand task (Alcazar et al., 2018b). On the other hand, the 5-STST, TUG and gait speed assessments may be subject to bias derived from human timing error, potentially limiting their reproducibility. In this context, SARC-T quantifies movement speed using a validated optoelectronic encoder and requires only two repetitions, which may reduce fatigue while providing objective and standardised measurement. These features support SARC-T as a complementary test to existing assessments of sarcopenia and physical performance and suggest potential integration into diagnostic pathways. Another relevant aspect is the difficulty of performing tests that assess sarcopenia severity, such as gait speed or TUG, in individuals with gait alterations, as may occur in people with sarcopenia and Parkinson’s disease. In such cases, freezing of gait or festinating gait could compromise test execution (José et al., 2013). Moreover, reduced handgrip strength secondary to osteoarthritis and fatigue in older adults could present a barrier to the application or interpretation of tests such as handgrip and gait speed (Vlietstra et al., 2019). From a practical standpoint, compared with time-based field tests (e.g., 5-STST, TUG, gait speed), SARC-T may offer an instrumented and standardised velocity output that could reduce manual timing error and provide complementary information on physical performance. Potential disadvantages include the need for specialised equipment and operator training, which may limit scalability in lower-resource settings.

From a feasibility and safety perspective, physiological variables (oxygen saturation, heart rate, and blood pressure) were broadly stable before and after SARC-T, and no statistically significant between-group differences were observed at baseline or immediately after testing. In the sarcopenia group, physiological responses during SARC-T were comparable to those observed during the other functional tests routinely used in sarcopenia evaluation, with no indication of a more concerning response pattern for SARC-T. These findings support the feasibility of administering SARC-T in very old adults and suggest that it can be performed without evidence of disproportionate physiological perturbation under the conditions tested (Fisher et al., 2015).

Since sarcopenia selectively affects skeletal muscle, the progressive loss of type II fibers, responsible for high-speed movements, may contribute to the reduced movement velocity observed in patients with sarcopenia (Nilwik et al., 2013; Larsson et al., 2019). This slower execution speed could imply a lower relative effort intensity during the task compared to non-sarcopenic individuals, which may partially explain the absence of marked physiological changes in this cohort. However, mechanistic interpretations should be made cautiously, and future studies incorporating objective measures of effort and exertion would be valuable.

The incorporation of an optoelectronic encoder enhances measurement accuracy by minimising assessor bias and enabling objective monitoring of performance (Ruiz-Alias et al., 2024). These features support SARC-T not only as an assessment instrument, but also as a potentially useful tool for tracking functional changes over time and for evaluating responses to interventions in clinical practice.

In clinical terms, SARC-T may be particularly valuable in situations where traditional assessments, such as the 5-STST, gait speed, or handgrip strength, are contraindicated or impractical. In older adults with advanced osteoarthritis, balance impairments, or multiple comorbidities, the low burden of a brief chair-rise velocity assessment and its feasibility in limited space may facilitate evaluation. Nevertheless, SARC-T requires a validated and calibrated measurement device, and the availability of such equipment may affect scalability in lower-resource settings. In primary care, SARC-T could be administered using a standard chair-rise task within a small clinical area, providing an objective complement when gait-based assessments are impractical. In institutional settings (e.g., long-term care), the brief two-repetition protocol may support assessment in very old adults with multimorbidity, provided that device availability and protocol standardisation are ensured.

In this sample of older adults, SARC-T showed moderate-to-strong associations with EWGSOP2-recommended functional tests and was able to discriminate between participants classified with sarcopenia and matched controls. In addition, under the protocol evaluated, physiological variables recorded before and after SARC-T remained broadly stable and were comparable between groups. Overall, these findings appear to support the use of SARC-T as a complementary performance-based measure for assessing physical function related to sarcopenia, particularly in settings where other tests may be less feasible.