Can the timed up and go test be used as a predictor of muscle strength in older adults?

ABSTRACT This study analyzed the timed up and go test (TUG) as a tool to evaluate muscle strength in community-dwelling older people. As a methodology, an observational, cross-sectional and analytical study was conducted. Data from 442 older people were analyzed, both women (71.7%) and men (28.3%). Ages ranged from 62- 104 years, with a mean of 80.85 (±8.047) years. TUG was used as a tool to evaluate muscle strength. Comparison and correlation analyses were performed to compare performance between the TUG and the chair stand test (CST) and between TUG and handgrip strength (HGS). Analysis of agreement between the diagnosis of low physical performance on TUG and the diagnosis of muscle weakness on CST and HGS was also performed. The predictive values were estimated using the receiver operating characteristic curve. The analyses showed a moderate direct proportional correlation between TUG and CST performance and low inversely proportional correlations between TUG and HGS performance and between CST and HGS (p<0.001). In the accuracy analyses, it was observed that TUG test could predict muscle strength in CST (S 34.4%; PPV 91.5%; NPV 26.1%; AUC=0.779; 95%CI 0.724-0.835; p<0.001) and handgrip dynamometry (S 44.2%; PPV 77.4%; NPV 67.2%; AUC=0.652; 95%CI 0.599-0.705; p<0.001). The Timed Up and Go test was able to satisfactorily indicate individuals with normal muscle strength in CST.

strength.Comparison and correlation analyses were performed to compare performance between the TUG and the chair stand test (CST) and between TUG and handgrip strength (HGS).

Analysis of agreement between the diagnosis of low physical
performance on TUG and the diagnosis of muscle weakness on CST and HGS was also performed.The predictive values were estimated using the receiver operating characteristic curve.The analyses showed a moderate direct proportional correlation between TUG and CST performance and low inversely proportional correlations between TUG and HGS performance and between CST and HGS (p<0.001).In the accuracy analyses, it was observed that TUG test could predict muscle strength in CST (S 34.4%; PPV 91.5%; NPV 26.1%; AUC=0.779;95%CI 0.724-0.835;p<0.001) and handgrip dynamometry (S 44.2%; PPV 77.4%; NPV 67.2%; AUC=0.652;95%CI 0.599-0.705;p<0.001).RESUMEN | Este estudio analizó el uso de la prueba de levantarse y andar (TUG) como una herramienta para evaluar la fuerza muscular en adultos mayores residentes en la comunidad.Como metodología, se trata de un estudio observacional, transversal y analítico.

INTRODUCTION
It is estimated that muscle strength progressively decreases 10%-15% from the fifth to the seventh decades of life 1,2 .This reduction in muscle strength and mass can influence loss of autonomy 3 , risk of frailty 4 , and sarcopenia 5 .Furthermore, it is known that reductions in muscle strength are more accurate predictors of mortality than changes in muscle mass 6 .
With the reduction of muscle strength resulting from aging, the identification of clinical tools to track muscle strength deficits becomes essential for adequate decisionmaking in health, which aims to prevent disabling injuries that affect the quality of life of older people and the quality of care in health systems 7,8 due to complications that can lead to consequences such as falls, functional limitations 9 , hospitalizations, and mortality 6 .Furthermore, this identification allows for diagnostic evaluation 3 , detection of specific early clinical interventions 6 , and reduction of the costs of health services 3 .
In this context, the timed up and go test (TUG) is a reliable tool for evaluating functional mobility, also presenting a significant correlation with the risk of falls, fear of falling, and functional performance 6,10 .However, it is also a possible screening tool for sarcopenia, due to the possibility of evaluating muscle strength and speed in a single test.This use of TUG was analyzed by the study by Filippin et al. 3 , in which they reported that the test presented adequate sensitivity (88.9%) to predict sarcopenia in older adults, as well as negative predictive value (93.2%) and a 0.66 area under the receiver operating characteristic (ROC) curve, and can be used as a screening tool.
Corroborating these results, Martinez et al. 6 observed that TUG presented 66.7% sensitivity, 88.7% specificity, and moderate accuracy (0.80; CI=0.66-0.94;p=0.001) for prediction of sarcopenia in older adults.Clegg et al. 11 used TUG as an indirect tool to evaluate muscle strength to stratify volume and training levels in an exercise protocol.Thus, such applications allow for expanding the use of TUG to evaluate muscle strength in older adults.
Therefore, this study aimed to analyze the use of TUG as a tool for assessing muscle strength in community-dwelling older adults, with the hypothesis that TUG would present discriminatory power to evaluate muscle strength.

METHODOLOGY
This is an observational, descriptive, cross-sectional, and analytical study.The data were obtained by the retrospective analysis of the medical records of older adults of a Geriatrics and Gerontology center of the Brazilian Federal District Health Department (SES-DF).
The sample consisted of a database of older adults.Medical records were collected from November 2021 to February 2022.Individuals were older adults (aged ≥60), of both sexes, who could walk independently for at least 10 meters, followed simple verbal commands, and responded to the collection tools, evaluated by the mini-mental state examination (MMSE) 12 .Older adults with severe sequelae of stroke, neurological diseases that prevented testing, needed a wheelchair or were bedridden, as well as those with severe cognitive impairment, evaluated by the clock drawing and verbal fluency tests 13 , were excluded.
Sample estimation was performed using the G*Power 3.1 program and indicated the need for a sample of 381 older adults.
Sample characterization was performed based on the following covariates: age, sex, schooling level, marital status, family income, body mass index (BMI), presence of comorbidities, and self-report of falls in the previous six months.TUG was the dependent variable.Handgrip strength (HGS) and the chair stand test (CST) were the independent variables.
TUG was used as a tool to evaluate muscle strength.This test quantifies functional mobility in seconds by standing up from a standardized chair, walking a linear course of three meters, turning, and returning to the chair, sitting down again 3 .The reference points for low physical performance adopted were values ≥20 seconds 14 .
HGS was evaluated using the Saehan® dynamometer in the dominant hand of each participant, following the recommendations of the European Consensus on Sarcopenia 15,16 , which defines muscle weakness scores <27kg/F for men and <16kg/F for women 14 .
CST is used in clinical practice to evaluate strength and resistance of lower limbs as a substitute for leg muscle strength, using the time required for a patient to stand up five times from a sitting position without their arms 14 .In this test, the score for muscle weakness is ≥15 seconds 14 .

Statistical analysis
Distribution of numerical data was tested by the Kolmogorov-Smirnov test.The comparisons between older adults with normal and low TUG results were performed using the Mann-Whitney U-test.The associations between the physical performance data in TUG and muscle strength in CST and HGS were analyzed by Spearman's correlation test and interpreted as follows: 0.26-0.49:low correlation; 0.50-0.69:moderate correlation; 0.79-0.89:high correlation; and finally, 0.90-1.00:very high correlation 17 .
The agreements between the diagnosis of low physical performance in TUG and muscle weakness in CST and HGS were evaluated using the Kappa statistic.Values ≥80% were considered as excellent agreement; values from 40%-60% were considered as moderate agreement; and values <40% were considered as weak agreement 18 .The number of weak and strong older adults with normal or low physical performance in TUG was obtained for each evaluation tool (CST and HGS).To analyze the accuracy of the tool studied (TUG), sensitivity (S), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) were estimated.ROC curves were built to verify the capacity of TUG measurements to discriminate strong and weak older adults in CST and HGS and the area below the ROC curve (area under the curve -AUC).Statistical analyses were conducted using the Statistical Package for the Social Sciences (SPSS) program version 22.0 (Franz Faul, Universität Kiel, Germany).

RESULTS
Data from 442 participants were analyzed.Participants had a mean age of 80.85 (±8.047) years, with the majority having a low schooling level -incomplete elementary school (55.4%) -and low income -up to three minimum wages (89.8%).Table 1 shows other sociodemographic and clinical characteristics and the participants' performance with the tools.When comparing the performance of HGS and CST, it was observed that older adults with normal TUG presented significantly higher HGS and were faster in CST when compared with those with lower TUG performance (p<0.001).Table 2 shows these data.Correlation analyses showed a moderate directly proportional correlation (r=0.606,p<0.001) between TUG and HGS performance and inversely proportional low correlations between TUG and HGS performance (r=−0.353,p<0.001) and between CST and HGS performance (r=−0.289,p<0.001).
The agreement analysis of the diagnoses of muscle strength of CST and HGS was not statistically significant (p=0.077).Table 3 shows the distribution of participants.Table 4 and Figure 1 show TUG validity estimates.

DISCUSSION
This study aimed to analyze the use of TUG as a tool to assess muscle strength in community-dwelling older adults.TUG satisfactorily discriminated individuals with normal muscle strength, presenting high specificity regarding CST.Its use in clinical practice implies differentiating and dispensing from health services those who do not need interventions with greater safety.
Older adults with normal TUG present higher HGS and were faster in CST when compared with older adults with low TUG performance.Similar to the results found by Benavent-Caballer et al. 19 , in which TUG performance was highly correlated with knee extension strength.Standing up from a chair is a motor task that requires a relevant effort of the lower limbs muscles, close to the maximum voluntary isometric contraction.Thus, it is expected that individuals with higher handgrip strength have shorter times in the execution of CST 20 .
We also found a moderate positive correlation between TUG and CST performance.We can infer that this result was obtained due to the relationship of both tests with the mobility and the muscle strength of the lower limbs.TUG is used to evaluate the performance related to the task 5 and the low physical performance, besides predicting adverse outcomes, is also used to categorize the severity of sarcopenia 14 .CST requires strength and endurance, mainly used as an alternative to measure the strength of leg muscles 14 .
However, the study showed inversely proportional low correlations between TUG performance and handgrip strength.These findings may be related to the inconsistency among studies on the evaluation of global muscle strength [21][22][23][24][25] .Studies 5,14,16,26 state that body measurements can be correlated, and grip strength may be related to lower limbs strength.However, muscles evaluated by handgrip dynamometers are not recruited in daily activities since static contractions are rarely used.Furthermore, other factors may influence HGS, including footprint size, genetic factors, and anthropometric variables 27 .
Chan et al. 28 observed a weak correlation between quadriceps strength and HGS in an older population, similar to our sample, whose mean age is 80.85 years.This occurs because older adults have more physical disabilities, which can distort correlation between limbs.
The results showed weak agreements among all tests, and the agreement between muscle strength in CST and handgrip dynamometry was not statistically significant.This finding may be a result of the sample size, considered relatively small for this type of analysis.
In this study, we observed that TUG has a satisfactory discriminatory capacity of muscle strength compared to CST due to the high specificity (91.5%) and high value of PPV (94.1%), that is, greater security to affirm that an individual with TUG≥20s presents muscle weakness.Martinez et al. 6 observed using the ROC curve analysis that TUG presented a high sensitivity of 66.7% and specificity of 88.7% in the prediction of sarcopenia in hospitalized older adults.Since it has higher specificity than sensitivity, it can be used as a confirmatory test, as it can reliably detect those without sarcopenia.
Unlike our study, using TUG in the discrimination of sarcopenia, Filippin et al. 3 found sensitivity of 88.9% and specificity of 31.4% using the ROC curve.Sensitive tests for early diagnosis are essential because they allow selecting patients who would benefit from specific early diagnosis and intervention.Thus, this test is a clinical tool for screening for sarcopenia 3 .
The findings presented in Table 4 show that for TUG validation, CST and HGS presented low accuracy regarding sensitivity.Thus, TUG is not suitable for screening individuals with muscle weakness, requiring better investigation with more sensitive tests for such use.
Furthermore, another interesting aspect about these results is that CST (TUG≥20s) presented PPV=94.1 and NPV=26.1,whereas HGS (TUG≥20s) presented PPV=57.0 and NPV=67.2.We believe that compatibility is related to CST presenting higher values of specificity and because HGS is a gold standard test for muscle strength evaluation, presenting higher sensitivity values.
The study has some limitations that may affect results interpretation.This is a retrospective study, using a database.Thus, we do not have some sample characterization variables, such as the score in the participants' MMSE and information on physical activity practice.Moreover, the lack of description of the amount of data excluded and the small sample size for the type of analysis of agreement between the tests are also limitations.
We recognize the limitations of the study, however, the findings reinforce that the use of the TUG test can facilitate discrimination between individuals who have normal muscle strength of those with muscle weakness and, thus, treat only those who require intervention, reducing costs in public health.Also, when using TUG for this purpose, the time while performing other tests is reduced, which is very beneficial considering this population's high demand for health professionals.Therefore, it is possible to help clinicians find and implement interventions focused on muscle strength gain for older adults.

CONCLUSION
In conclusion, the timed up and go test (TUG) showed a moderate correlation compared to CST and satisfactorily indicated individuals with normal muscle strength in HGS.Thus, it can be used in clinical practice to exempt individuals from health services with greater safety when they do not require intervention.

Table 4 .Figure 1 .
Figure 1.Receiver operating characteristic curves with significant measurements of the timed up and go test to discriminate muscle strength in the chair stand and handgrip strength tests

Table 2 .
Comparison of handgrip strength performance and chair stand test among groups of older adults with normal scores and low timed up and go test performance

Table 1 .
Continuation Table3.Distribution of participants with normal strength and muscle weakness in the chair stand and handgrip strength tests among those with normal and low timed up and go test scores