Diagnostic accuracy of the Fast Timed Up and Go test for identifying low lower-limb functional power in community-dwelling Thai older women: a cross-sectional study using sit-to-stand-derived muscle power as the reference standard
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The Fast Timed Up and Go (FTUG) test is a simple mobility assessment that may serve as a practical alternative for identifying low lower-limb functional power in community settings. This study aimed to evaluate the diagnostic accuracy of FTUG for detecting low functional power and to determine an optimal population-specific cutoff in community-dwelling older Thai women.
Methods
A cross-sectional diagnostic accuracy study was conducted among 88 community-dwelling women aged ≥60 years. Relative sit-to-stand (STS) muscle power was calculated using the Alcazar equation, and low power was defined as a value below the 25th percentile of the sample distribution (2.36 W/kg). Diagnostic accuracy of FTUG was evaluated using receiver operating characteristic (ROC) analysis, with the optimal cutoff identified using the Youden index.
Results
Participants with low STS-derived power demonstrated significantly slower FTUG times than those with normal power (12.43±3.72 seconds vs. 8.33±1.08 seconds, P<0.001). ROC analysis showed strong discriminatory capacity, with an area under the ROC curve of 0.922 (95% confidence interval, 0.855–0.989). The optimal FTUG cutoff was 9.8 seconds, yielding 77.3% sensitivity and 93.9% specificity. Alternative thresholds showed acceptable performance but did not exceed the overall accuracy of the 9.8-second cutoff.
Conclusion
FTUG demonstrated high diagnostic accuracy for identifying reduced lower-limb functional power in community-dwelling older Thai women. A population-specific cutoff of 9.8 seconds may provide a practical tool for early screening in community health settings.
Preserving lower-limb muscle function is a central determinant of mobility and independence among older adults. This issue has gained particular relevance in Thailand, where demographic transition is progressing rapidly, and older adults now comprise more than 20% of the population [1]. Within this group, older women often experience accelerated neuromuscular decline owing to hormonal and musculoskeletal changes following menopause. These changes contribute to reduced strength, balance impairments, and mobility limitations [2,3]. For clinicians and community health workers, identifying early signs of functional decline is increasingly important to prevent disability and reduce the future care burden.
Accumulating evidence in geriatric science indicates that muscle power, rather than muscle strength or muscle mass alone, is a more sensitive indicator of age-related mobility decline, because the capacity to generate force rapidly deteriorates earlier and more markedly with aging and certain clinical conditions [4-6]. This decline affects essential daily activities, such as rising from a chair, accelerating gait, and negotiating stairs. Therefore, the concept of powerpenia has emerged to describe a clinically significant reduction in muscle power that is distinct from sarcopenia and dynapenia [5].
Although gold-standard measurements such as isokinetic dynamometry or force platforms provide precise estimates of power, their cost and technical requirements limit their feasibility for large-scale or community-level use. Sit-to-stand–derived (STS) muscle power has become a practical field alternative method and is supported by evidence linking it to functional capacity and adverse outcomes [7,8]. However, calculating STS power requires measurement steps and equations that are unfamiliar to many primary care and community practitioners.
In contrast, the Timed Up and Go (TUG) test is a well-established and internationally recognized assessment tool widely used in geriatric research and clinical practice, including Thailand, owing to its simplicity and minimal equipment requirements [9-11]. The fast variant of the test, the Fast Timed Up and Go (FTUG), may be particularly informative because it requires rapid movement initiation, dynamic balance, and turning control, all of which depend on lower-limb muscle power [12,13]. In community-dwelling older adults in Thailand, clear performance differences are often observed when individuals are instructed to perform the TUG test as quickly as possible, which supports the potential of the FTUG as an efficient proxy for functional muscle power. However, no studies have examined the diagnostic accuracy of the FTUG in detecting low muscle power among older Thai adults or established population-specific cutoffs.
This study aimed to (1) determine the diagnostic accuracy of the FTUG for identifying low lower-limb functional power using STS relative muscle power as the reference standard and (2) identify an optimal FTUG cutoff appropriate for communitydwelling Thai older women. Establishing such a threshold may facilitate practical screening in community health settings, where time, personnel, and equipment are limited.
Methods
Study design and setting
This study employed a cross-sectional diagnostic accuracy design and was conducted in several community areas in Phayao Province, northern Thailand. Locations such as multipurpose community halls and public spaces commonly used for local health promotion activities were selected to ensure that participants were familiar and comfortable with the environment. All data collection procedures were administered by physical therapists with prior experience working with older adults who were trained specifically for this project to maintain consistency across testing sessions. This study complied with the principles of the Declaration of Helsinki. Ethical approval was obtained from the Human Ethics Committee of the University of Phayao (approval no., HREC-UP-HSST 1.2/088/67). Before participation, participants received an explanation of the study procedures and provided written informed consent.
Participants
The participants were community-dwelling women aged ≥60 years. Recruitment was facilitated through local health volunteers and community announcements, which are a routine approach for research conducted in rural and semi-urban Thai settings. To be eligible, individuals were required to (1) be at least 60 years old, (2) walk independently for a minimum distance of 10 m (use of a cane was permitted if regularly used in daily life), and (3) understand and follow verbal instructions. The exclusion criteria were as follows: (1) acute illness or unstable cardiovascular or neurological conditions; (2) severe musculoskeletal pain or recent lower-limb surgery interfering with testing; (3) uncontrolled hypertension (>180/100 mm Hg); and (4) severe cognitive impairment preventing protocol completion.
As no previous research has examined the use of the FTUG for identifying low functional power, a pilot study with 30 participants was conducted to estimate preliminary sensitivity and specificity. Using these pilot estimates (sensitivity, 70.46%; specificity, 68.85%) and applying the formulas recommended for diagnostic accuracy research with a 10% margin of error and a 95% confidence interval (CI) level, the minimum required sample size was calculated to be 80. The target sample size was increased by approximately 10% to account for potential missing data or dropouts, resulting in a final sample size of at least 88 participants.
Procedures
Data were collected during scheduled community visits. After confirming eligibility, participants completed a structured interview covering demographic characteristics and medical histories. This step was followed by functional performance assessments, including the FTUG test and the five-times sit-to-stand (FTSTS) test. The order of the tests was randomized using simple randomization to reduce potential sequence effects.
Fast Timed Up and Go
The FTUG test was used to assess functional mobility at a maximal safe speed. The procedures were adapted from the original TUG protocol described by Podsiadlo and Richardson [9], with modifications emphasizing rapid performance. Participants sat on a standard-height chair (43–45 cm) with their backs against the backrest and arms resting on their thighs. At the verbal cue “Start,” they were instructed to stand up, walk 3 m as quickly and safely as possible, turn around a cone, return to the chair, and sit down until their back touched the backrest. Timing commenced at the initiation of the verbal cue and ended once the participant had fully contacted the chair. Because older adults may vary in familiarity with rapid-movement tasks, three familiarization trials were conducted before data recording. The average time of the recorded trials was used for analysis. Participants were allowed to use their usual assistive devices (e.g., a cane) if this reflected their normal mobility. Previous studies have demonstrated high reliability of this test (intraclass correlation coefficient, 0.97–0.99), supporting its suitability for community-based screening [14,15].
Five times sit-to-stand
The FTSTS test was used to assess lower-limb muscle strength and functional performance [16]. The test has demonstrated moderate correlations with knee extensor strength (r=–0.388 to –0.634) [17]. Participants sat on a standard armless chair (seat height 44 cm) with their backs straight, arms crossed over the chest, and feet positioned such that the heels were approximately 10 cm behind the knees, with the hips flexed at 90°. At the command “Start,” participants were instructed to stand up and sit down five consecutive times as quickly and safely as possible without using their arms. Timing began at the initiation of the verbal cue and stopped when the participant’s back contacted the chair after the fifth repetition. Three trials were performed, separated by brief rest periods, and the mean time across the trials was used for analysis [15,18].
Classification of low lower-limb functional power
Low lower-limb functional power was based on the STS muscle power obtained from the FTSTS, which is recognized as a standardized and valid field measure of lower-limb functional power.
Step 1: Calculation of relative muscle power
Relative STS power (W/kg) was calculated for each participant using the validated formula proposed by Alcazar et al. [7]:
Relative STS mean power(W/kg)=Body mass×0.9×g×[(height×0.5)−h]FTSTS time×0.1
where g represents gravitational acceleration (9.81 m/s²) and h denotes chair height. This method estimates the average mechanical power output relative to body mass, which is particularly useful for community-based assessments.
Step 2: Determination of the Thai-specific cutoff and classification of participants
To classify low power, the distribution of relative power values in the sample was examined. Following approaches used in international studies and adapted to reflect the characteristics of older Thai women, the 25th percentile was selected as the cutoff. In the present dataset, this corresponded to 2.36 W/kg. Therefore, participants with relative power values below 2.36 W/kg were categorized as having low functional power (powerpenia), whereas those at or above this threshold were considered to have normal power.
Statistical analysis
Descriptive statistics were used to summarize participants’ characteristics, including frequencies, percentages, means, and standard deviations. The diagnostic accuracy of the FTUG test for identifying low STS muscle power was evaluated using receiver operating characteristic (ROC) curve analysis. The ROC curve plots the true-positive rate (sensitivity) against the false-positive rate (1−specificity) across a range of possible threshold values, thereby illustrating the trade-off between sensitivity and specificity for the diagnostic test [19]. The area under the ROC curve (AUC) was calculated to quantify the overall discriminatory power of the FTUG test in detecting low muscle power. An AUC of 0.5 indicates no discriminatory ability, whereas values between 0.7–0.8, 0.8–0.9, and >0.9 represent acceptable, excellent, and outstanding accuracy, respectively [20]. The optimal cutoff was determined using the Youden index (J=sensitivity+specificity−1) to maximize the combined sensitivity and specificity [20,21]. Data analysis was performed using IBM SPSS ver. 24.0 (IBM Corp.) and Stata/SE ver. 14.1 (StataCorp LP).
Results
A total of 88 community-dwelling older women participated in the study and completed all assessments. Their mean age was 68.01±6.30 years. Participants were able to ambulate independently without the need for walking aids, although several reported occasionally using assistive devices. More than half of the sample (n=52) reported having at least one chronic noncommunicable disease, most commonly hypertension, diabetes mellitus, hyperlipidemia, cardiovascular disease, or scleroderma. None of these conditions presented symptoms severe enough to interfere with test performance. No adverse events occurred during the physical assessments.
Table 1 summarizes the baseline characteristics and performance outcomes for the total sample and for participants categorized into normal- and low-power groups. As expected, women classified as having low functional power were significantly older than those in the normal-power group (72.64±7.66 years vs. 66.14±4.56 years, P<0.001). Relative STS power also differed markedly between groups (1.64±0.29 W/kg vs. 2.21±0.22 W/kg, P<0.001), supporting the validity of the percentile-based classification approach. Performance on the FTSTS and FTUG was substantially slower in the low-power group.
ROC analysis demonstrated that FTUG had excellent discriminatory performance in identifying low lower-limb functional power, with an AUC of 0.922 (95% CI, 0.855–0.989; P<0.001) (Figure 1). The sensitivity, specificity, and Youden index were calculated across all observed FTUG values to determine the optimal threshold. The highest Youden index (J=0.712) was obtained at an FTUG cutoff of 9.8 seconds, yielding a sensitivity of 77.3% and a specificity of 93.9% (Table 2).
Several nearby cutoffs demonstrated acceptable diagnostic performance, including 9.2 seconds (sensitivity 81.8%, specificity 86.4%) and 9.6 seconds (sensitivity 77.3%, specificity 90.9%). However, none exceeded the overall discriminatory balance achieved at the 9.8-second threshold, which provided the optimal trade-off between sensitivity and specificity. The complete diagnostic indices for all evaluated cutoffs are presented in Table 2.
Discussion
The present study evaluated the diagnostic accuracy of the FTUG in identifying low STS muscle power in community-dwelling older Thai women. The FTUG test demonstrated strong discriminatory capacity, reflected by an AUC of 0.922, indicating that the test can distinguish individuals with reduced lower-limb functional power with a high degree of accuracy. The cutoff of 9.8 seconds, determined using the Youden index, provided a sensitivity of 77.3% and a specificity of 93.9%. When combined with a percentile-based classification using the 25th percentile of STS power, these findings suggest that the FTUG may serve as a practical screening tool for early identification of functional decline in community and primary care settings where more complex assessments are not feasible.
These results align with those of previous studies, emphasizing the importance of muscle power as a predictor of mobility limitation, disability, and frailty. Earlier studies have demonstrated that muscle power declines earlier and more rapidly than muscle strength and is strongly associated with functional performance, particularly in tasks requiring rapid movement [4,22]. The validity of using STS power as a field measure of neuromuscular capacity was also supported by Alcazar et al. [7], who showed that the STS power test reflects the demands of common daily activities. Further evidence from Alcazar et al. [23] provided robust normative data and established functionally relevant cutoff points for relative STS muscle power in a large European cohort, showing that relative STS power declined progressively with advancing age and that low relative STS power was strongly associated with mobility limitations in older adults. The current findings build on this body of literature by demonstrating that the FTUG, a simple and widely available mobility test, may serve as a reasonable proxy for detecting individuals with low STS power.
Prior research on the TUG has focused primarily on the usual-pace version, which is commonly used to screen for frailty, fall risk, and general mobility decline [9]. This emphasis is supported by evidence that walking speed, even when assessed at a usual pace, serves as an integrative indicator of functional capacity and overall health status in older adults [24]. However, few studies have explored fast-paced variations [14,25]. The FTUG test incorporates rapid initiation, stepping acceleration, turning, and controlled sitting tasks, which place greater demands on neuromuscular power and dynamic stability. Fast-paced versions of the TUG can be conceptualized as a functional “stress test” of mobility because the task sequence includes repeated transitions and continuous control of the body’s center of mass during standing, gait initiation, walking, turning, and controlled sitting, thereby increasing demands on dynamic balance and neuromotor control relative to usual-pace walking in daily life [9,13,14]. When the same multi-component task is performed “as fast as safely possible,” successful performance requires not only adequate strength but also rapid force generation and coordination, which are core features of neuromuscular power and are strongly linked to functional trajectories in older adults [7]. Consistent with the broader geriatric literature, faster mobility performance can therefore be interpreted as reflecting greater physiological reserve and higher overall functional capacity, given that walking speed is a robust indicator of health and function and is consistently associated with major outcomes in older adults, including adverse events and survival [24,26]. This may explain why the FTUG test in this study effectively discriminated between older adults with normal and those with low STS power.
Clinically, the 9.8-second cutoff offers a practical tool for primary care and community health providers, particularly in settings with limited resources. The FTUG requires minimal equipment, has a short administration time, and can be performed by non-specialists with adequate training. The high specificity of the cutoff supports its potential use as an initial screening tool to identify older adults who may benefit from targeted interventions such as power-focused resistance training, balance training, or more comprehensive functional evaluations. This is especially relevant in Thailand, where the proportion of older women is increasing, and community-based screening tools are needed to support the early detection of mobility decline. Thus, the present findings provide a clinically meaningful reference point that may inform practice in health promotion clinics, community centers, and primary care units. In addition to their clinical utility, these findings have several practical implications. The FTUG test can be incorporated into routine community health assessments to identify early functional changes before more pronounced mobility limitations emerge. Screening results may help guide decisions regarding referral for physical therapy, community-based exercise programs, and tailored strength and power training. In low-resource areas, the FTUG provides an accessible option for regular monitoring of mobility status among older adults.
The strengths of this study include the use of a validated STS power equation, standardized testing procedures, and multiple FTUG trials to enhance measurement reliability. This study also provides population-specific FTUG data for older Thai women, contributing to a regional evidence base in which research on functional power assessment remains limited. However, this study had several limitations. First, the study sample consisted exclusively of independently mobile older women, which may limit generalizability to men, individuals with mobility impairments, or other populations. This population homogeneity, while enhancing internal validity, restricts broader extrapolation of the findings. Second, low muscle power was operationally defined using the 25th percentile of relative muscle power derived from the study sample. This sample-derived, population-specific threshold was intentionally used as a pragmatic reference standard for this exploratory diagnostic accuracy study and should not be interpreted as a universal or outcome-based clinical cutoff. Thresholds based on prospective associations with adverse outcomes may differ across populations. Third, the cross-sectional design precludes assessment of predictive validity; therefore, the ability of the FTUG to predict future adverse outcomes, such as falls, hospitalization, disability, or long-term functional decline, cannot be determined. Future research should prioritize external validation of the FTUG cutoffs in more diverse populations, including men, individuals with varying levels of functional ability, and different sociocultural contexts. Longitudinal studies are also warranted to establish outcome-based thresholds and examine whether FTUG performance predicts clinically meaningful events. Furthermore, interventional studies evaluating whether FTUG-based screening followed by targeted muscle power training improves mobility or reduces adverse outcomes would strengthen its clinical applicability. Consideration of cultural and lifestyle factors specific to Asian populations may further refine interpretations in community and primary care settings.
In summary, the FTUG test demonstrated strong diagnostic accuracy in identifying low STS power among community-dwelling older Thai women. Its simplicity, short administration time, and minimal equipment requirements make it suitable for integration into routine assessments in primary care and community health programs. Early identification of low functional power may support timely interventions aimed at maintaining mobility, independence, and overall quality of life among older adults.
Notes
Conflict of interest
No potential conflict of interest relevant to this article was reported.
Acknowledgments
We sincerely thank all volunteers for their participation and the village health volunteers for their support in facilitating community access and field data collection. We used an AI-based tool solely for English language editing to improve grammar and clarity. This tool was not used to generate scientific content or interpretations. All analyses, conclusions, and statements represent the full academic responsibility of the authors.
Funding
This study was supported by University of Phayao and Thailand Science Research and Innovation Fund (Fundamental Fund 2025, Grant No. 5029/2567).
Data availability
Data of this research is available from the corresponding author upon reasonable request.
Author contribution
Conceptualization: all authors. Data curation: PP, WD. Formal analysis: PP, WD. Funding acquisition: PP. Investigation: PP, WT. Methodology: PP, WD. Supervision: PP. Validation: PP, WT, AT. Writing–original draft: PP, WD. Writing–review & editing: PP, WD. Final approval of the manuscript: all authors.
Figure. 1.
The area under the receiver operating characteristic (ROC) curve of the Fast Timed Up and Go test. CI, confidence interval.
Table 1.
Demographic data and measurement outcomes
Variable
Total (n=88)
Normal power (n=63)
Low power (n=25)
P-value
Age (y)
68.01±6.30
66.14±4.56
72.64±7.66
<0.001
BMI (kg/m2)
23.03±4.32
22.80±3.70
23.62±5.64
0.506
Body weight (kg)
52.61±10.69
52.08±9.25
53.94±13.80
0.467
Relative power (W/kg)
2.05±0.35
2.21±0.22
1.64±0.29
<0.001
FTSTS (s)
10.93±2.70
10.09±1.10
13.47±4.18
<0.001
FTUG (s)
9.36±2.72
8.33±1.08
12.43±3.72
<0.001
Values are presented as mean±standard deviation.
BMI, body mass index; FTSTS, five-times sit-to-stand; FTUG, Fast Timed Up and Go.
Table 2.
Diagnostic performance of alternative FTUG cutoffs for identifying low lower-limb functional power
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Diagnostic accuracy of the Fast Timed Up and Go test for identifying low lower-limb functional power in community-dwelling Thai older women: a cross-sectional study using sit-to-stand-derived muscle power as the reference standard
Figure. 1. The area under the receiver operating characteristic (ROC) curve of the Fast Timed Up and Go test. CI, confidence interval.
Graphical abstract
Figure. 1.
Graphical abstract
Diagnostic accuracy of the Fast Timed Up and Go test for identifying low lower-limb functional power in community-dwelling Thai older women: a cross-sectional study using sit-to-stand-derived muscle power as the reference standard
Variable
Total (n=88)
Normal power (n=63)
Low power (n=25)
P-value
Age (y)
68.01±6.30
66.14±4.56
72.64±7.66
<0.001
BMI (kg/m2)
23.03±4.32
22.80±3.70
23.62±5.64
0.506
Body weight (kg)
52.61±10.69
52.08±9.25
53.94±13.80
0.467
Relative power (W/kg)
2.05±0.35
2.21±0.22
1.64±0.29
<0.001
FTSTS (s)
10.93±2.70
10.09±1.10
13.47±4.18
<0.001
FTUG (s)
9.36±2.72
8.33±1.08
12.43±3.72
<0.001
FTUG cutoff score (s)
Sensitivity (%)
Specificity (%)
Youden index
8.0
100.0
37.9
0.379
8.4
95.5
47.0
0.424
8.6
95.5
59.1
0.545
8.8
90.9
72.7
0.636
9.0
86.4
80.3
0.667
9.2
81.8
86.4
0.682
9.4
77.3
89.4
0.667
9.6
77.3
90.9
0.682
9.8
77.3
93.9
0.712a)
10.0
68.2
95.5
0.636
10.4
68.2
95.5
0.636
11.0
59.1
97.0
0.561
Table 1. Demographic data and measurement outcomes
Values are presented as mean±standard deviation.
BMI, body mass index; FTSTS, five-times sit-to-stand; FTUG, Fast Timed Up and Go.
Table 2. Diagnostic performance of alternative FTUG cutoffs for identifying low lower-limb functional power
FTUG, Fast Timed Up and Go.
The highest Youden index (J=0.712) was obtained at an FTUG cutoff of 9.8 seconds.
