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Summary

The instrumented Timed Up and Go (iTUG) test is gaining increasing attention in body sway and gait analysis with the development of new technologies. We present a protocol to analyze the subcomponents of the iTUG with motion capture.

Abstract

Despite efforts made by medicine and technology, the incidence of falls in older adults is still increasing. Therefore, early detection of the falling risk is becoming increasingly important for falling prevention. The Timed Up and Go (TUG) test is a well-accepted tool to assess mobility and can be used in predicting future fall risk in aged adults. In clinical practice, the total time to complete the test is the main outcome measure of the TUG test. Owing to its simplicity and generality, the traditional TUG test has been considered a global test for movement analysis. However, recently, researchers have attempted to split the TUG test into subcomponents and have updated its score system for further investigations. The instrumented Time Up and Go (iTUG) test, which is a new modification of the traditional TUG test, has been reported to be a sensitive tool for predicting movement disorders and the risk of falls in older adults. The goal of the present study was to analyze the iTUG test subcomponents using motion capture technology, and to determine which iTUG test subtasks are related to the potential risk of future falls.

Introduction

Falling is one of the most common geriatric syndromes and is the second leading cause of accidental or unintentional injury-related deaths worldwide¹. In adults aged above 65 years, falling can result in functional impairment, disability, decreased quality of life, increased length of stay in hospitals, and even mortality^2,3. Therefore, preventing falls is of utmost importance.

To determine predictors of fall events, previous researchers have focused on gait analyses, balance tests, mental state, sedative drug use, as well as history of falling in the preceding year^4,5 The Timed Up and Go (TUG) test is a quick performance-based measure of mobility. The TUG test has been extensively studied in older adults and is recommended as a simple screening test for the risk of falls⁶. This widely used test consists of rising from a chair, walking 3 m at the preferred speed, turning around, returning, and sitting. The traditional clinical outcome of this test depends on its total duration⁷ and is assessed by a stopwatch.

In clinical practice, the conventional TUG test measures the total time to perform a series of activities without dividing the performance of the subject into subcomponents⁸. Recently, some investigators have proposed that different TUG test components might be particularly sensitive as predictors of future falls⁹. When using the digitized instrumented TUG (iTUG) test, the individual components of the TUG test can be analyzed separately. By using the iTUG, it is possible to objectively evaluate several characteristics of each TUG test sub-phase and obtain quantitative data, such as the relevant durations, velocities, and angular velocity of each movement. With more detailed data, the iTUG test has shown the advantage of detecting specific deficits that may be more indicative of the fall risk¹⁰.

As the gold standard in movement analysis, motion capture technologies have been used to detect movement in patients with Parkinson's Disease (PD)¹¹, cognitive impairment¹², and ankle arthritis¹³, as well as in healthy adults¹⁴. In the current study, we aimed to analyze the iTUG test subcomponents using motion capture technology and to determine the correlation between iTUG test subtasks and the potential risk of future falls.

Protocol

This study was approved by the Academic Ethics Committee of the Seventh Medical Center of Chinese PLA General Hospital in Beijing, China.

1. Participant inclusion/exclusion criteria

1. Recruit aged participants 65 years or older and obtain their informed consent.
2. Exclude participants who have obvious visual and lower limb disability, such as knee arthritis, thromboangiitis obliterans, and gout.

2. Preparation of the test area

1. Set up the standardized iTUG test area of 5 m x 8 m or wider (see Figure 1) with 12 cameras distributed around the room. Put the traditional TUG setups into the test area: a chair and a sign to remind the participant to turn back.
   NOTE: Signs indicating route lines are optional.
2. Ensure that the motion capture area is limited to the scope of all the cameras and all the TUG test setup is non-light reflective.

3. Software preparation for the procedures before the test

1. Install the motion capture software on the computer to be used in the room.
2. Click the Seeker button to start the motion capture software. After starting the software, for General Camara Configuration, choose the default mode (frame rate = 60 frames/s, shutter speed = 1/1,000 s), which is acceptable for most situations. Set Selected Camera Settings and Camera Configuration Settings also in the default mode.
3. Select Live mode to set the real-time settings.
   NOTE: Post mode is used to analyze the data captured.
4. Click on Markersets to configure the marker settings.
5. Select XY axis in the Calibration of Ground Axis and millimeters in Calibration units.
6. Click on Calibrate to select the calibration variation.
7. Select Initial Calibration and click on the "L" shaped button. At the same time, take the "L" shaped calibrator into the field and put it in the center of the field to make sure it can be captured by all the cameras.
   NOTE: The "L" shaped calibrator contains four light-reflective markers.
8. Check on the screen whether all the 12 cameras can detect four reflective markers. If any camera detects ≤3 markers, reduce lightness and threshold at the left of the screen. If any camera detects ≥5 markers, check the field and clean or cover the unwanted reflective markers.
   NOTE: Some tiny belongings of the former participant might be detected by the camera.
9. Remove the "L" shaped calibrator from the field.
10. Click on the "T" shaped button. At the same time, take the "T" shaped calibrator into the field and wave it to make sure it can be captured by all the cameras.
11. Select Z axis in the Calibration of Up Axis and millimeters in Calibration units.
12. Have the doctors check whether all the cameras can capture the markers. Wave the markers in each corner of the field, especially covering the possible space of the TUG test.
13. Check in the screen whether all 12 cameras can detect the "T" shaped calibrator. If any camera cannot detect it, change the direction of the camera.
    NOTE: There are two shapes of markers that need to be calibrated; "L" shaped and "T" shaped. The "L" shaped calibrator has four light-reflective points to calibrate the XY axis, and the "T" shaped calibrator has four light-reflective points to calibrate the Z axis. The calibration duration will last 60 s or more. An effective capture will turn the color of the screen green.
14. Click Finish to complete the calibration.
15. Click Save Calibration to store the effective calibration mode.
    NOTE: The calibration is performed in a 2D model; a 3D model is often used during the test.

4. iTUG test

NOTE: The participants should wear tight but comfortable clothes and shoes.

1. Attach the reflective points on the anatomical landmarks: cervical 7 spinous process andthoracic 10 spinous process, left acromion and right acromion.
   NOTE: Each participant could have up to 17 reflective points attached. The more reflective points that are attached, the more accurate the data collected, but also the less comfortable the participants feel.
2. Right-click the reflective points at the right line of the screen and nominate them as C7, T10, left shoulder, and right shoulder.
3. Show the instruction to the participants. The instruction is "Please rise from the chair, walk 3 m at your preferred speed, turn around, return, and sit."
4. Ask the participants to perform the iTUG test beforehand to make sure they are familiar with the instruction.
   NOTE: Make sure each participant is comfortable after the reflective points are attached.
5. Instruct the participant to perform the iTUG test.
   NOTE: The participants need to walk to complete the iTUG task.
6. While the participant is performing the iTUG test, click the start and stop buttons on the screen of the computer.
   NOTE: During the iTUG test, the motion capture system samples data from all attached points at a frequency of 60 Hz; a video is formed accordingly (see Video 1).

5. Data collection and definition of iTUG test variables

1. Click the Recording Setting button.
   NOTE: The data are stored and found in a spreadsheet.
2. Select Raw Camera Data |Tracked ASCTI | Tracked Binary. The Capture Duration is 20 s.
3. Type in the name of the participant.
4. Click the Record button to start data collection.
5. Identify sub-phases of the iTUG test by reviewing the video and calculate the variables according to the data.
   1. Define the following variables: traditional TUG test total time, phase 1 time (rising from the chair), phase 1 body sway (rising from the chair), phase 2 time (walking 3 m at the preferred speed), phase 2 body sway (walking 3 m at the preferred speed), phase 3 time (turning around), phase 3 body sway (turning around), angular velocity of phase 3 (turning around), phase 4 time (returning), phase 4 body sway (returning), and phase 5 time (sitting).
      NOTE: The details are similar to those described by Caronni and colleagues¹⁵.

6. Downton Fall Risk Index (DFRI)

1. Assess the falling risk using the Downton Fall Risk Index (DFRI).
   NOTE: The DFRI (Table 1) includes 11 risk items, which are scored one point each. Scores are summed to a total index score, range 0-11. A score of ≥3 is considered to indicate a high risk of falls. To evaluate falling risk, DFRI is usually used for participants admitted in a hospital, and the Home Falls and Accidents Screening Tool (HOME FAST) is more suitable for community dwellers.

7. Statistical analysis

1. Use a commercially available statistical software package to perform all statistical analyses. Use Student's t-test to assess group differences and choose Pearson correlation coefficient to assess the relationship between subcomponents of iTUG and DFRI score on the total sample, with P ^< 0.05 indicating a statistically significant difference.
2. Use the Bland-Altman procedures to assess agreement for Phase 1 duration, Phase 3 angular velocity, and Phase 4 duration between our method and the McRoberts sensor (see the Table of Materials). Calculate the mean difference between the two methods of measurement and the 95% limit of agreement for the mean difference calculated.

Representative Results

Thirteen aged participants with a high risk of falling (DFRI score: 3-11) and 11 aged subjects with a low risk of falling (DFRI score: 0-2) were recruited. The DFRI is detailed in Table 1. As has been mentioned previously, a score of 3 or more is considered to indicate a high risk of falls for patients during hospitalization¹⁶.

Demographic data are shown in Table 1, which includes gender, age, TUG test score, and iTUG test variables. As shown in Table 2, there were no significant differences regarding sex and age between groups. A marginal difference existed between groups in the TUG test score (15.4 ± 5.3 s vs 11.2 ± 5.5 s, P = 0.056). The TUG test score was based on the traditional way (completion time). Individuals with a high risk of falling exhibited a significantly higher phase 3 duration (2.8 ± 1.5 s vs 2.0 ± 0.9 s, P = 0.023) and phase 4 duration (2.9 ± 1.6 s vs 2.1 ± 1.0 s, P = 0.024), as well as a lower phase 3 angular velocity (1.2 ± 0.4 º/s vs 1.7 ± 0.4 º/s, P = 0.021), in comparison with those at low risk of falling. The variables related to body sway were not significantly different between groups.

As shown in Table 3, there existed a significant correlation between the DFRI score and Phase 1 duration, Phase 3 duration, Phase 3 angular velocity, Phase 4 duration, as well as Phase 5 duration. However, we did not find similar trends between DFRI and the sway variables of each phase of iTUG.

As demonstrated in Figure 2, Bland-Altman plots suggested that the agreement between iTUG and the Dynaport accelerometer sensor was acceptable for Phase 1 duration, Phase 3 angular velocity, and Phase 4 duration. There were one (5%), zero (0%), and one (5%) outliers from the 1.96 standard deviation value for Phase 1 duration, Phase 3 angular velocity, and Phase 4 duration, respectively.

Figure 1:The subcomponents of the instrumented Time Up and Go test. (A) Before Phase 1: person sitting on the chair. (B) During Phase 2: on his way toward the viewer. (C) During Phase 3: going around the chair in the front. (D) During Phase 4: back toward the original chair. Abbreviation: iTUG = instrumented Time Up and Go. Please click here to view a larger version of this figure.

Figure 2: Bland-Altman plot for comparing iTUG and Dynaport accelerometer sensor. (A) Bland-Altman plot for Phase 1 duration using iTUG and Dynaport accelerometer sensor. (B) Bland-Altman plot for Phase 3 angular velocity using iTUG and Dynaport accelerometer sensor. (C) Bland-Altman plot for Phase 4 duration using iTUG and Dynaport accelerometer sensor. Please click here to view a larger version of this figure.

Items	Score
Known previous falls
Yes	1
No	0
Medications
Tranquillizers/sedatives	1
Diuretics	1
Antihypertensives (other than diuretics)	1
Antiparkinsonian drugs	1
Antidepressants	1
Other medications	1
None	0
Sensory deficits
Visual impairment	1
Hearing impairment	1
Limb impairment	1
None	0
Mental state
Confused (cognitively impaired)	1
Orientated	0
Gait
Unsafe (with/without walking aids)	1
Safe with walking aids	0
Normal (safe without walking aids)	0
Unable	0

Table 1: The Downton fall risk index items and scoring system. A DFRI score above 3 points indicates a high risk of falling. Abbreviation: DFRI = Downton fall risk index.

	High risk of falling	Low risk of falling	P value
	(n=13)	(n=11)
Gender, M/F	“3/10”	“4/7”	0.08
Age, years	74.29 (6.61)	70.40 (9.23)	0.077
TUG score, s	15.4 (5.3)	11.2 (5.5)	0.056
Phase 1 duration, s	1.4 (0.4)	1.2 (0.2)	0.56
Phase 1 sway, °	123.3 (68.9)	110.3 (57.7)	0.684
Phase 2 duration, s	2.9 (1.0)	2.8 (1.4)	0.924
Phase 2 sway, °	141.3 (72.6)	132.2 (48.6)	0.082
Phase 3 duration, s	2.8 (1.5)	2.0 (0.9)	0.023*
Phase 3 angular velocity, °/s	1.2 (0.4)	1.7 (0.4)	0.021*
Phase 4 duration, s	2.9 (1.6)	2.1 (1.0)	0.024*
Phase 4 sway, °	119.8 (64.1)	113.5 (55.7)	0.936
Phase 5 duration, s	4.6 (1.7)	3.5 (1.5)	0.063
Value = Mean (Standard deviation)

Table 2: Demographic data and instrumented Time Up and Go test variables of the participants. Significant differences in the phase 3 duration, phase 4 duration, and phase 3 angular velocity were observed between groups.

	DFRI	r value	P value
Phase 1 duration, s		0.347	0.007*
Phase 1 sway, °		0.061	0.804
Phase 2 duration, s		-0.026	0.898
Phase 2 sway, °		0.287	0.174
Phase 3 duration, s		0.462	0.020*
Phase 3 angular velocity, °/s		-0.403	0.003*
Phase 4 duration, s		0.487	0.000*
Phase 4 sway, °		0.312	0.137
Phase 5 duration, s		0.568	0.000*
Higher r value represents a close relationship
DFRI = Downton Fall Risk Index

Table 3: Correlations between DFRI score and subcomponents of iTUG. Significant correlation between DFRI score and Phase 1 duration, Phase 3 duration, Phase 3 angular velocity, Phase 4 duration, as well as Phase 5 duration. Abbreviations: iTUG = instrumented Time Up and Go; DFRI = Downton fall risk index.

Video 1: An example of an iTUG task. Please click here to view this video.

Discussion

The critical steps in the protocol are to attach the reflective points accurately to the anatomical landmarks to avoid bias. Furthermore, the identification of each subcomponent of the iTUG test is also a critical step; a video review is helpful for the identification.

A marginal difference existed between groups in the TUG test scores implying that traditional TUG scores might not be sensitive enough to discriminate risk of falling. We did not find obvious differences between the groups in Phase 1 duration and Phase 5 duration, and this could be explained by the fact that all the participants did not show abnormalities in lower limb strength. Phase 1 duration is associated with lower limb strength in aged individuals with a high risk of falling^17,18. Phase 3 angular velocity reported to be a key point associated with vestibular hypofunction, together with Phase 3 duration, was found to be correlated with the DFRI score¹⁹. The high risk of falling in older adults might be caused by a sense of dizziness related to vestibular hypofunction.

There are four limitations to this method. First, the motion capture system is currently expensive; however, this system will become increasingly more economical with the development of the technologies. Second, the specific test room is also a potential challenge. As has been mentioned previously, some belongings of participants lost on the floor might be detected as a reflective point; therefore, the room needs to be cleaned carefully. In addition, this motion capture system-based iTUG test needs much more space than the traditional TUG test. The traditional TUG test only needs 3 m x 2 m and hence, it can be performed in many places (e.g., corridor, test room, ward). While the room for the iTUG test should be larger than 32 m² because the cameras are installed around the room. Third, the reflective points can impact the compliance of the participants. The more reflective points attached, the lower may be the comfort level reported. The researchers should confirm whether the reflective points influence the mobility of the participants. Fourth, iTUG test is an expensive measurement relative to the traditional TUG test.

The TUG test is a commonly used way to evaluate movement and risk of falling²⁰. However, except for the completion time, the doctors can hardly get more information from the traditional version. Whereas, iTUG has highlighted points to show more details. The significance of this method is that it subdivides the traditional TUG test with a motion capture system, providing new variables regarding time and body sway. Our results demonstrated that some subcomponent time variables, rather than body sway variables, differed between groups. The motion capture system can also be used in the tandem walking and Romberg test to highlight the disequilibrium in patients with PD, cerebellar ataxia, and sports concussions^21,22,23. As recent studies have evidenced that the TUG test subcomponents are associated with cognitive function,^6,24 this method can also be used in screening for cognitive impairment.

Materials

Black strip	Deli	60 mm x 20 m
Calibrator	NOKOV	reflector marker1	L shape
Calibrator	NOKOV	reflector marker2	T shape
Chair	YUANSHENGYUANDAI	“10076062317820”
Computer	HUAWEI	HONOR
McRoberts sensor	DynaPort Hybrid, McRoberts, The Hague, The Netherland
Motion capture camera	NOKOV	Mars2H
Motion capture software	NOKOV	DG-01
Reflective marker	NOKOV	small marker	for calibrators
Reflective marker	NOKOV	large marker	for participants