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The PhyStat 7: A New Test Battery for Characterizing the Physical Status of Older Adults

Bohannon, Richard W. PT, DPT, EdD, NCS, FAPTA

Topics in Geriatric Rehabilitation: April/June 2017 - Volume 33 - Issue 2 - p 84–88
doi: 10.1097/TGR.0000000000000142
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This observational study was undertaken to describe a battery of 7 measurements of physical status, the PhyStat 7, and to determine the time requirements and clinimetric properties of the battery. Ten men and 10 women (aged 60-79 years) were examined during 2 sessions 10 to 14 days apart. A younger comparison group of 10 men and 10 women (aged 20-29 years) was also examined. During the first session, each of 2 testers independently obtained 7 measurements from all participants: (1) body mass index (BMI); (2) tragus-to-wall (TTW) distance; (3) unipedal stance time (UST); (4) 5-repetition sit-to-stand (STS) time; (5) grip strength; (6) gait speed; and (7) 2-Minute Walk Test (2MWT) distance. During the second session, 1 of the 2 testers repeated the 7 measurements with the older participants. The PhyStat 7 took an average of 12 minutes to administer. For individual items of the PhyStat 7, intraclass correlation coefficients (ICCs [model 3,1]) describing intertester reliability ranged from 0.712 to 0.997 and ICCs describing test-retest reliability ranged from 0.676 to 0.998. For a total PhyStat 7 score derived by adding z-transformed individual items, the ICCs for intertester reliability and test-retest reliability were 0.939 and 0.893, respectably. Content validity was supported by loadings on 2 factors—physical structure (BMI and TTW distance) and physical performance (UST, STS time, grip strength, gait speed, and 2MWT). Known-groups validity was demonstrated by significant differences between the older and younger groups in all items except BMI and gait speed.

Department of Physical Therapy, Campbell University College of Pharmacy and Health Sciences, Buies Creek, North Carolina.

Correspondence: Richard W. Bohannon, PT, DPT, EdD, NCS, FAPTA, Department of Physical Therapy, Campbell University College of Pharmacy and Health Sciences, Buies Creek, NC 27506 (bohannon@campbell.edu).

The author claims no conflicts of interest relative to the work, financial or otherwise.

An immense body of research has established that physical status deteriorates with advancing age—particularly in the presence of geriatric syndromes such as frailty1 and sarcopenia.2 This deterioration has been documented using a wide array of tests and measurements. These measurements include gait speed3 and grip strength,4 which have been proposed for use as vital signs of physical status for older adults. Beyond such individual measurements, multidimensional batteries of measurements have also been recommended to more thoroughly characterize the physical status of older adults. Among such batteries are the Short Physical Performance Battery,5 the Functional Fitness Battery,6 and the Senior Fitness Test.7 Although there is considerable research involving these batteries, health care professionals do not routinely use them to document the physical status or longitudinal changes in the physical status of older adults. Perhaps, a battery that is both practical and more broadly informative might realize wider application. We sought therefore to describe a battery of 7 physical status measurements that could be performed quickly and easily in a host of settings. We also sought to describe the reliability and validity of the measurements in the context of the overall battery.

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METHODS

This observational study, which was conducted at a university research laboratory, was approved by the institutional review board of the University of Connecticut (protocol H13-078). Participants were enrolled and tested from October 2014 to March 2015. All provided written informed consent. Ten men and 10 women (aged 60-79 years) were examined during 2 sessions 10 to 14 days apart. A younger comparison group of 10 men and 10 women (aged 20-29 years) was also examined. During the first session, each of 2 trained testers independently in random order obtained 7 measurements from all participants. During the second session, 1 of the 2 testers randomly repeated the 7 measurements with the older participants. Intertester and test-retest reliability and content validity were determined for the measurements obtained from the older participants. Known-groups validity was determined by comparing PhyStat 7 measures between the older and younger age groups.

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Participants

Inclusion required that would-be participants: (1) were living independently in the community and were not using an assistive device for gait, (2) were 60-79 or 20-29 years of age, (3) self-rated their health as at least fair, and (4) had walked at least a quarter mile or 2 minutes without stopping sometime during the previous 6 months. Participants were excluded from the study if they were under the care of a physician for conditions such as syncope or unstable exertional angina, which would have put them at risk during the testing.

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Measurements

Seven quantitative measurements were selected on the basis of their established use, practicality, and measurement properties. The specific measurements focused on body composition, posture, strength, balance, gait, and functional exercise capacity.

Body composition was described using body mass index (BMI), that is, body mass (kg) divided by height (m) squared. Although more specific measures of body composition exist, BMI is notably simple, fast, and inexpensive. Moreover, BMI is the item (#128) within the Physician Quality Reporting System used for screening for underweight and obesity.8 The validity of BMI is supported both by its association with other measures of body composition9 and by the association of both low and high BMIs with adverse outcomes.10 The reliability and responsiveness of BMI are also established.11,12 Reference values are available.13 In our study, body mass was obtained while participants stood lightly clothed, without shoes, on a calibrated digital scale. Height was determined while participants stood without shoes, looking straight ahead, with their backs against a measuring tape fixed to a wall. The BMI was calculated by entering body mass and height into a smartphone application.

Posture, which is not included in well-known batteries of physical status, was described using the tragus-to-wall (TTW) distance; that is, the perpendicular distance between the wall and the tragus of the ear. Although other objective measures of posture are available, the TTW distance is particularly simple, fast, and inexpensive. In addition, TTW distance can be measured while participants are fully clothed. The validity of the measure is supported by its correlation with radiographic measures and other measures of spinal posture.14,15 Both test-retest reliability and intertester reliability have been demonstrated.14,15 Responsiveness of the measure has been substantiated.16 Reference values are available.17 In our study, TTW distance was measured while participants stood with their back and buttocks against the wall and their feet against an 8.0-cm board placed on the ground against the wall. The tester used a metric ruler to measure the perpendicular distance from the wall to the left and right tragii while participants stood “relaxed and looked straight ahead.” The criterion TTW distance was the average of the measurements of the left and right sides.

Strength was described using 2 measures—the 5-repetition sit-to-stand (STS) test and grip strength. Although performance on the STS test is dependent upon more than just strength,18 the test is widely used with older adults and is a part of other test batteries.5,7 It is simple, fast, and inexpensive. The association of 5-repetition STS time with other measures of lower limb strength,19 as well as with other important outcomes,20 supports its validity. The test-retest reliability of the test is established as is its responsiveness.21–23 Reference values are available.24 In this study, a stabilized standard chair with a 43.2-cm (17.0-in) high seat and no armrests was used. Participants were asked to sit forward on the chair and “fold your arms, stand all the way up, and sit down firmly as fast as possible 5 times.” Testers started timing with a stopwatch at the participants' first movement and stopped timing with the completion of their last stand-up time. The tester counted repetitions aloud. Two 5-repetition trials separated by 30 seconds were performed. The better (shorter) of the 2 trials was the criterion measure. Grip strength is widely used as an indicator of overall muscle strength25 and is a component of various test batteries.1,2 Its measurement is simple and fast. The only expense of consequence is that of the dynamometer. Grip strength is associated with both current and future outcomes of importance.26 Its reliability is firmly established21,22 as is its responsiveness.22,27 Reference values are available.28 In our study, grip strength was measured with a Jamar dynamometer in its second handle position. Participants sat in a chair with their arms against their sides and their elbows flexed 90°. They were told to “squeeze as hard as you can” and encouraged by the testers' monotone “harder, harder, harder.” Two trials separated by a 30-second hiatus were performed on each side. The better (higher) of the 2 trials, regardless of side, was the criterion measurement.

Balance was described by the time that participants could maintain balance on 1 foot (unipedal stance time [UST]). Although subject to both ceiling and floor effects, depending on the population, the test is widely used and is simple, fast, and inexpensive. The validity of UST is supported by the association of UST with alternative measures of balance, as well as with other important outcomes.29,30 Some researchers have found the test to have acceptable reliability.31 It is responsive to changes accompanying an exercise regimen.32 Reference values are available for UST.33 In our study, participants balanced on their preferred foot for up to 45 seconds. They were instructed to “slowly lift your other foot and maintain your balance as long as possible.” Timing began when the foot was first lifted from the floor and ended when the foot returned to the floor, the stance limb was displaced, or 45 seconds had elapsed. Two trials were completed with an intervening 30-second rest unless the participant balanced 45 seconds on the first trial. The longer duration of the 2 trials was the criterion measure.

Gait performance was characterized by the speed at which participants walked. Gait speed is widely used alone and in combination with other measures as a health status indicator.5,34,35 It is simple, fast, and inexpensive and is adaptable to different settings. The validity of gait speed is supported by its association with different measures of mobility and other important outcomes.36 Its reliability and responsiveness are well established.36 Reference values are available.37 For this study, participants were instructed to “walk at your normal comfortable speed.” Timing began when participants' midsagittal line crossed a starting line after an acceleration of 1.52 m (5 ft) and ended after their midsagittal line crossed a finish line 6.1 m (20 ft) beyond and 1.52 m (5 ft) before a stop line. Two trials were separated by a 30-second rest. The faster of 2 trials was the criterion measure.

Functional exercise capacity was characterized using the 2-Minute Walk Test (2MWT). The 2MWT is being used increasingly in lieu of the 6-Minute Walk Test, as it requires less time and yields results that are highly correlated with those of the 6-Minute Walk Test.38 The 2MWT is reliable and responsive.39 Moreover, there are reference values available.39 The 2MWT involved a 15.2-m (50-ft) course, with ends marked by cones. Participants were instructed to “walk back and forth around these cones, try to cover as much ground as possible without running, you are allowed a standing rest if required, but resume walking as soon as possible.” At 1 minute, the tester said, “You are doing well, you have 1 minute remaining.” The distance covered at 2 minutes was the criterion measurement.

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Data analysis

The Statistical Package for the Social Sciences (SPSS 18.0) was used for all analysis. For the sample of older adults, intertester and test-retest reliability of individual items and total scores was established using intraclass correlation coefficients (ICCs [model 3,1]). Total scores were derived by summing z-transformed item scores. Factor analysis with varimax rotation was used to establish content validity. For known-groups validity, PhyStat 7 item measures obtained from the older and younger groups were compared using t tests (equal variance not assumed).

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RESULTS

The mean (SD) of ages was 68.9 (6.9) (range, 60-82) for the older group and 23.2 (1.4) (range, 21-26) for the younger group. All were white. Self-rated health was excellent (n = 12), good (n = 7), or fair (n = 1) for participants in the older group and excellent (n = 14) or good (n = 7) for participants in the younger group. All participants completed the PhyStat 7 without incident. Completion of the PhyStat 7 by participants of the older group required between 9 and 15 minutes.

Table 1 summarizes PhyStat 7 measures and findings relevant to reliability. For individual items of the PhyStat 7, ICCs describing intertester reliability ranged from 0.712 to 0.997 and ICCs describing test-retest reliability ranged from 0.676 to 0.998 (Table 2). For a total PhyStat 7 score, the ICCs for intertester reliability and test-retest reliability were 0.939 and 0.893, respectively. Content validity was supported by loadings on 2 factors (Table 2)—physical performance (STS time, grip strength, UST, and 2MWT, eigenvalue = 2.727) and physical structure (BMI and TTW distance, eigenvalue = 1.666). Known-groups validity was demonstrated by differences between the older and younger groups. The effect sizes for the differences were generally moderate to strong. The differences were significant for TTW distance, STS time, grip strength, UST, gait speed, and 2MWT (Table 3).

TABLE 1

TABLE 1

TABLE 2

TABLE 2

TABLE 3

TABLE 3

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DISCUSSION

This study thoroughly describes a battery of 7 simple items, which when combined can be completed on average in about 12 minutes. The only equipment required to complete the battery are a stopwatch, weighing scale, ruler, measuring tape, standard chair, traffic cones, and handgrip dynamometer. While not inclusive of all potentially informative aspects of physical status (eg, flexibility and coordination), it does include fitness measures addressed by other established batteries (ie, strength, balance, speed, and endurance) and measures of body composition (ie, BMI) and posture (ie, TTW distance) that are neglected by other physical status batteries.40

The reliability and validity of all of the measures of the battery have been reported before.* Excluding UST, all the individual measures of the PhyStat 7 demonstrated acceptable reliability. The exception of UST is based on the lack of variance between participants in UST. Many of the participants were able to maintain UST for the full 45 seconds. By z-transforming participant scores on individual items, it was possible to establish both intertester reliability and test-retest reliability of PhyStat 7 sum scores. The PhyStat 7 was shown to have both content and known-groups validity. The 2 aspects of content addressed, physical performance and physical structure, represent an important expansion beyond the content of some other batteries. Bodily structure, as represented by both body composition (BMI) and forward flexed posture (TTW distance), has important health consequences. Known-groups validity was expected for all of the measures except BMI. Thus, only gait speed did not differ significantly between groups as expected. As the effect size between groups for gait speed was moderate, it is reasonable to conclude that the study was merely underpowered for the variable.

This study had several limitations. Chief among them was the sample of participants tested; it was small, of convenience, and racially homogeneous. Such a sample may be sufficient for testing reliability or validity,41 but it is far too small to estimate responsiveness statistics (eg, minimal detectable change) or norms for PhyStat 7 items. There is, however, plentiful relevant information on responsiveness12,16,22,23,27,32,36,39 and norms13,17,24,28,33,37,39 for the individual PhyStat 7 measures obtained in different contexts.

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CONCLUSIONS

The PhyStat 7 is a parsimonious battery of tests with sufficient reliability and validity to warrant widespread use. Once an older individual's scores on the battery are known, judgments as to physical status and changes in physical status requiring intervention can be made.

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* References9–12,14,15,19–21,22,26,29–31,36,38,39.
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Keywords:

clinimetrics; measurement; older adult; screening

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