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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 61:718-725 (2006)
© 2006 The Gerontological Society of America

Evaluating Task Modification as an Objective Measure of Functional Limitation: Repeatability and Comparability

Todd M. Manini, Summer B. Cook, Tom VanArnam, Moshe Marko and Lori Ploutz-Snyder

1 Department of Exercise Science, Syracuse University, New York.
Departments of 2 Physical Therapy and 3 Physical Medicine Rehabilitation, SUNY Upstate Medical University, Syracuse, New York.

Address correspondence to Todd Manini, PhD, Laboratory of Epidemiology, Demography and Biometry, National Institute on Aging, Gateway Bldg., Suite 3C-309, 7201 Wisconsin Ave., Bethesda, MD 20892-9205. E-mail: maninit{at}mail.nih.gov


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
Background. Modification of everyday tasks in older adults is associated with risk of deleterious health outcomes. The purpose of this study was to develop a task modification scale to examine its reliability and comparability to timed performance and common measures of physical function and impairment.

Methods. Eighty-two (21 men, 61 women) older adults (74.4 ± 8.2 years) were observed performing a chair rise (sitting heights: 43 cm, 38 cm, and 30 cm), stair ascent/descent, and kneel and supine rise tasks. Six hierarchically ranked categories (0–5) of modification were created for each task and then summed across tasks (summary modification [MOD] score: range 0–35). Comparisons were made with timed performance, knee extension strength, single-leg balance, self-reported function, five chair stands, and gait speed.

Results. Inter-rater reliability (intra-class correlation = 0.98) and participant repeatability (intra-class correlation = 0.92) of the MOD score were excellent. Ninety-six percent of participants modified at least one task (MOD score: 10.5 ± 7.51, range 0–27). After adjusting for task modification, timed performance showed a lower association with gait speed (time vs MOD score, semipartial r2 = 0.31 vs 0.68), strength (semipartial r2 = 0.14 vs 0.65), and single-leg balance (semipartial r2 = 0.10 vs 0.40) than did the MOD score. The MOD score showed higher correlations with muscle strength and balance impairment than did other measures of functional limitation such as gait speed, time to complete five chair stands, and self-reported physical function.

Conclusion. Documentation of task modification is reliable across raters and repeatable within participants; in addition, it compares well with other measures of physical function and impairment. Task modification reveals important and intuitive information regarding physical limitation, and deserves greater attention.

MANY older adults change the way in which they perform tasks of everyday living as in relying on the handrail to climb the stairs or on the armrests to rise from a chair (1). These modifications are thought to narrow the gap between physical ability and the demands set by the environment (2). Although task modification is well known to occur among older adults (1,3), it has yet to be considered as an objective measure of task performance. This lack of investigation into task modification is partially attributed to the already well-known objective performance tests that use timed performance as a proxy for functional limitation (4,5). The existing scales perform well and are sensitive to change in large population studies but ignore if or how older adults modify tasks. Because task modification has intrinsic meaning (more modification equals more adaptation to the environment), it provides a descriptive measurement of limitation for both clinical and research settings.

The onset of disability involves a complex interaction between functional limitation and societal influences. Accurate assessment of functional limitation and/or disability should account for a person's ability as well as for the demands of the environment. For example, timed performance provides an estimation of functional limitation only when the tasks are performed in a standardized environment without the influence of task modification (5,6). In contrast, placing older adults in a flexible environment where they can modify the task reveals strategies that allow continued success in society. Therefore, task modification offers insight into a possible link between functional limitation and outright disability, as it represents a middle step between the two and may be one good indicator of preclinical disability (7).

Optimally, a record of both timed performance and task modification gives researchers and clinicians a better understanding of overall ability. However, information regarding the impact that task modification has on timed performance is needed. Knowing this relationship would help to determine whether task modification truly indicates a loss in function that is independent of timed performance.

Proponents of performance batteries suggest that timed task completion is more sensitive than categorized measures because time is a continuous variable (8,9). This advantage is thought to help identify early declines in functional ability (8). Task modification can also be developed into a semicontinuous measure by quantifying subtle ways in which older adults complete demanding tasks. These subtle methods may be uniform among older adults and can be categorized across several tasks of varying difficulty. A semicontinuous measure of task modification will offer a sensitive and important descriptive component to understanding physical limitation—how older adults overcome environmental demands and continue to function in society.

Previous research suggests that older adults who self-report modifying a task, but do not report difficulty, are at risk for subsequent disability (10). These findings show that older adults behave according to their ability, but may not recognize that they are having difficulty (11). These studies are limited to self-reported task modification, which is constrained, as are most self-reported data, to an individual's perception. A directly observed scale that objectively quantifies varying degrees of modifications meets a need to expand task modification into an inclusive measurement in the pathway to disablement. Developing this scale for a variety of tasks with different degrees of difficulty will help identify those persons beginning or relying on task modification. Individuals beginning to use subtle modifications could be targeted for intervention in a preclinical state of disability.

The primary purpose of this study was to develop an objective task modification scale that may be used to estimate physical ability at an intermediary step prior to disability. Other purposes included understanding how task modification affects timed performance and evaluating inter-rater reliability, test–retest repeatability, and comparison to other measures typically used in the literature to document age-related change in both functional performance and physiological impairment.


   METHODS
Top
 Abstract
 Methods
Results
 Discussion
 References
 
Participants
Eighty-two older adults (21 men and 61 women: average age 74.4 ± 8.2 years) completed the testing protocol. The recruitment goal for the primary participant sample was to identify moderate to lower functioning older adults between the ages of 50 and 100 years to adequately examine the relationship of task modification and timed performance. Advertisements were posted and presentations were made at local senior centers. Phone interviews were conducted during which potential participants were asked about their ability to rise from a chair and to climb a flight of stairs. When potential participants indicated "some" or "a lot of difficulty" performing the task they were invited for testing. Prior to testing, all potential participants responded to a health questionnaire to determine if physician clearance was required to enter the study (12). A physician clearance was required for participants who answered yes to certain risk factors (i.e., heart attack, hypertension, musculoskeletal pain). Participants were not invited for testing if they had cardiac or pulmonary difficulty in the prior year. Participants were living independently in the community, and all but two provided their own transportation to the testing facility. Syracuse and SUNY Upstate Medical University's Institutional Review Boards reviewed and approved the protocol. All participants gave written informed consent.

Task Modification Scale Development
Five tasks were chosen to evaluate task modification: a chair rise, stair ascent/descent, kneel rise, and supine to stand. All tasks were video recorded in the frontal plane, and timed performance was measured within 0.01 seconds using a digital video recorder. One investigator video recorded the participant performing the task while the other monitored the participant. The monitoring investigator followed the participant during the stair ascent/descent tasks and stood closely during the chair rise, kneel rise, and supine to stand tasks. No adverse events were documented during the testing. To avoid possible task order bias and carryover effects, all tasks were randomly ordered for each participant. The average length of time for testing was {approx}15 minutes.

Chair rise.-- Participants attempted to rise from three seat pan height (distance from sitting surface to the floor) chairs of 43 cm, 38 cm, and 30 cm. The variations in chair heights were chosen to increase the amount of difficulty rising from a chair (13) and to simulate some everyday challenges. To standardize the chair rise task, participants were asked to place their back against the backrest and then position their heels against a piece of wood that was directly in line with the edge of the seat pan. Directions were, "On the word ‘Go’, please rise from this chair as quickly as possible with your hands across your chest."

Stair ascent/descent.-- Participants were asked to ascend and then descend one flight of stairs (11 steps, step height = 19 cm). Directions were, "Climb/Descend this flight of stairs as fast as comfortably possible. If you do not need the handrail please do not use it, but if you absolutely need the handrail please use it."

Kneel rise.-- Participants were asked to kneel on a carpeted floor with the right knee and place the left knee at a {approx}90-degree angle. With a chair placed in front, the participant was instructed to cross their hands across their chest and, "Rise to a standing position. Do not use the chair unless absolutely necessary." Participants repeated the task with the opposite leg, and the side with the better results was used for data analysis.

Supine rise.-- During the supine to stand task, participants were asked to lie on a carpeted floor in a supine position with their arms to their sides. When in the supine position, a chair was placed approximately 0.90 meters from the participant. Directions for the task were to "Rise from the floor to a standing position. Please do not use the chair unless absolutely necessary."

Task modifications were identified during pilot testing of nine older adults when they were asked to perform each of the tasks described previously. The video record was presented to a physical therapist with 15 years clinical experience and to an exercise physiologist with 5 years experience evaluating functional ability in elderly persons. Scale development began by categorizing the most common ways in which older adults perform each task (Table 1). The next step was to create an ordinal scale that indicated a gradient of difficulty performing each task. This gradient of difficulty was further established by consulting previous reports on maneuvers and existing assessments of the chair rise (14,15), stair ascent/descent (3), and kneel and supine rises (16,17). Those participants who used no identifiable modifications received a score of 0. Eight categories were first created, but because some categories overlapped, they were combined with the most closely resembling category. For example, the first version of the stair ascent/descent task included two categories of "Non-constant brushing with the handrail" and "Light continuous grasp of the handrail," which were later combined into one category, "Non-constant brushing/grabbing or light continuous grasp of the handrail."


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  		Table 1. Task Modification Scale.

 
We created a summary modification (MOD) score by summing the scores on all the tasks. A higher MOD score represents more task modifications, refusal, or inability to perform the tasks. As the scale is created from seven tasks each with five nonzero categories, the possible scoring range is 0–35. We also examined the applicability of removing three tasks (43 cm chair rise, 30 cm chair rise, and kneel rise) to create a reduced MOD score (MODred: score range = 0–20). These tasks were removed because of overlap with the 38 cm chair and supine rise tests. We imputed times for those participants who refused or needed assistance with the 90th percentile of time to complete the task. We also wanted to explore a simple solution to combining timed performance and MOD score by multiplying each MOD score by the timed performance and then summing over each task (MOD*time). This calculation was also done with the reduced version of the summary task modification (MOD*timered).

Inter-Rater and Test–Retest Reliability
We wanted to examine possible differences in rating task modification between investigators. Two raters with varying levels of experience (1 year and 5 years experience) rating elderly persons on task performance were chosen to examine the inter-rater agreement. To do this, 30 participants were randomly sampled from the total sample pool, and both raters viewed their video record separately.

To examine test–retest reliability, 40 of the 82 participants were asked to return to the laboratory in 10 weeks to repeat testing. During the follow-up testing, participants were given the same tasks and scripted directions, but in a different order.

Comparison Tests
A secondary purpose of the study was to compare MOD scores to measures of physiological impairment and functional measurements. Comparison tests included gait speed (fast and normal), five chair rises, self-reported physical function via a standard survey (Short-form 12 [SF-12]), knee extensor (KE) strength, and single-leg balance.

Gait speed.-- Participants were asked to walk at a normal pace and then as fast as comfortably possible. The distance (7.62 meters) was divided by the time to derive the gait speed.

Five chair rises.-- We used the EPESE (Established Populations for Epidemiologic Studies of the Elderly; 6) chair rise where participants rise up and down as quickly as possible from a 43 cm seat pan height chair with their hands across their chest. Timed performance was categorized according normative data presented elsewhere (4).

SF-12.-- Self-reported physical function and the physical composite score were documented via the SF-12 version 2 survey (18). Self-reported physical function (SF-12 version 2, questions 2a and b) and physical composite scores were calculated using norm-based scoring algorithms (19).

KE strength.-- Participants were seated in a KE dynamometer (MedX, Ocala, FL) with their knees oriented at 60 degrees of full extension. Pelvic and calf restraints were placed over appropriate regions and tightened. During the KE strength test, participants were instructed to kick their legs as hard and as fast as possible and maintain maximal voluntary isometric contraction for {approx}2 seconds. Participants repeated strength tests until two consecutive trials were within 5% of each other. Strength values were measured in Newton-meters and divided by body mass (kg).

Single-leg balance time.-- While standing behind a chair, participants were asked to place their hands across their chest, lift their left leg, and stand for as long as possible. Those participants who could stand for more than 30 seconds (excellent balance) were asked to stop the test. The time recorded from two trials was summed and used for data analysis.

Data Analysis
Median splines were used to describe the impact of task modification on timed performance. This method calculates the median time for each level of task modification and then uses it as a knot (i.e., breakpoint) to fit a cubic spline.

Both inter-rater and test–retest reliability of the MOD score were examined in each task using the quadratic weighted kappa statistic (20) and Spearman rank correlation. The intra-class correlation (ICC) was used to examine the reliability of the MOD, MODred, MOD*time, and MOD*timered.

Regression models were used to determine independent relationships of task modification and timed performance with comparison tests. To control for multicollinearity, we regressed timed performance on task modification and calculated a residual timed performance that was unrelated to task modification. Statistical significance was set at an alpha level of p ≤.05. All statistical analyses were done with STATA version 8.0 (College Station, TX).


   RESULTS
Top
 Abstract
 Methods
 Results
Discussion
 References
 
Persons who participated in the study self-reported similar physical function and physical composite score when compared to a normative sample of adults 75 years old or older (physical function: 39.5 ± 10.9 vs 40.6 ± 10, physical composite score: 39.5 ± 9.8 vs 40.8 ± 8.9) (19). The number of participants performing the specific modification along with the mean timed performance for each task are outlined in Table 2. The inter-rater and test–retest reliability for individual tasks (average weighted kappa: 0.82, range 0.55–0.95) were excellent (Table 2). All Spearman rank correlations were high and represented good reliability between raters and reproducibility within participants. The MOD and MODred scores showed excellent inter-rater reliability and within-participant repeatability (Spearman rank and ICCs ≥0.90). The MOD*time and MOD*timered also showed excellent participant repeatability (Pearson and ICC >0.90).


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  		Table 2. Mean Timed Performance (Seconds), and Inter-Rater and Test–Retest Reliability With Each Modification Score.

 
Figure 1 shows that timed performance is dependent on task modification. As suspected, when participants used assistive devices on the chair (armrest) and stairs (handrail) the time to complete the task was either reduced (mean change: 51% for 43 cm, 40% for 38 cm, 32% for 30 cm) or unchanged when compared to not using assistive devices. When participants relied heavily on the chair for assistance during the kneel or supine rise, the timed performance increased (34% and 50% greater from light to forceful use of hands for kneel and supine rise, respectively).


Figure 01
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  		Figure 1. Median spline plots of timed performance versus task modification

 
Three regression models were developed to examine the effect of task modification and timed performance (Figure 2). When the summed timed performance (90th percentile imputed for refused or needed assistance, 30 cm chair: n = 2, kneel rise [cannot kneel to floor]: n = 5, supine rise: n = 10) was plotted against MOD score, a point where the relationship degraded was noted. When the entire distribution was examined, much of the variance in timed performance was explained by MOD score (R2adj = 0.70). However, the relationship degraded at an MOD score of 11, a point at which participants were using on average 1.6 modifications per task, which represents a level of transition from no or little to severe use of task modification. This point of inflection was confirmed using segmented linear regression with the breakpoint placed at an MOD score of 12 (p =.05). There was a 24% reduction in variance explained when comparing ≤11 modifications (R2adj = 0.59) to >11 modifications (R2adj = 0.35). The intercept for those participants with ≤11 modifications was 21.0 seconds and >11 modifications was –0.64. The difference between these intercepts is 21.64 seconds, which is the predicted reduction in timed performance resulting from task modification. This represents a 36.4% average predicted drop in timed performance resulting from task modification (average summed timed performance for >11 modifications = 59.42 seconds; 21.64/59.42 * 100 = 36.4%).


Figure 02
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  		Figure 2. Plot of summed timed performance and summary modification (MOD) score. Degradation in the relationship between timed performance and modification occurred at an MOD score >11 (average 1.6 MOD score/task)

 
When compared to summed timed performance, MOD and MODred scores showed slightly lower correlations with gait speed and higher correlations with the EPESE chair stand, self-report function, single-leg balance time, and KE strength (Table 3). For self-reported physical function, MOD or MODred scores showed marginally higher correlations when compared to EPESE chair stand and gait speed. A direct comparison with the EPESE chair stand revealed that the MOD or MODred scores had higher correlations with gait speed (fast: 0.68 vs 0.53; normal: 0.62 vs 0.36), KE strength (0.64 vs 0.52), and single-leg balance time (0.41 vs 0.39). The MOD*time and MOD*timered increased the variation between participants and, except for correlations with gait speed, reduced many of the associations.


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  		Table 3. Comparison of the MOD Score and Timed Performance to Other Measures of Physical Performance.

 
To account for the dependency between modification and time, we regressed timed performance on task modification and used the residuals to determine the independent relationship with gait speed, KE strength, and single-leg balance time. All models showed that MOD score was more related to gait speed, KE strength, and single-leg balance time when compared to summed timed performance residuals (Table 4).


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  		Table 4. Comparisons of Summed Timed Performance Unrelated to Task Modification.

 

   DISCUSSION
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 Abstract
 Methods
 Results
 Discussion
References
 
Previous studies show that self-reported task modification is related to the onset of disability (11), lower self-rated mobility ability (1), and functional limitation, measured by timed performance (21). Our data strengthen previous reports and suggest that objective observation of task modification is independently associated with estimates of functional limitation, physiological impairment, and self-reported physical function. Furthermore, the MOD score showed excellent inter-rater reliability and participant repeatability, and was more associated with physiological impairment and gait speed when compared to other common measures of physical function.

The hierarchical development of task modification represents an ordered progression of difficulty, which was developed by consulting existing literature (3,15,16) and experience working with older adults. For this scale to be applicable, it is essential that an ordered progression of difficulty exist. For example, in the chair rise, applicability relies on the fact that participants will progress in difficulty by first stomping feet, then scooting forward on the chair and then using hands on the chair for assistance. The instructions were developed to reveal modifications that older adults use to complete tasks of everyday living and to provoke maximal performance. Task modification would be impossible to quantify without these specific directions because participants may perform the modification out of convenience rather than necessity.

Of the seven tasks performed, both the kneel rise and the supine rise seemed to be the most difficult. For example, on the supine rise, four participants needed assistance and six participants refused to perform the task. We ranked refusal as the highest score based on claims that a prior incident (falling and not being able to get up) or strong belief that they would not be able to rise even with assistance was driving their fear of performing the task. Participants who refused to perform the supine task were in the highest MOD score decile (>23 modifications) and had higher MOD scores compared to those who needed assistance (MOD score = 18).

We recognize that timed performance is important and has been used to successfully document functional limitation (22,23). However, when attempting to quantify how older adults behave in the environment, timed performance suffers at the expense of task modification. Furthermore, the relationship between timed performance and task modification was significantly reduced when participants used more than 11 modifications for all tasks. Therefore, we believe that task modification can be used alone or in addition to timed performance to document physical function. When faced with a choice of measure, we recommend using both to fully understand the changes that occur during intervention or disease. This is especially true during interventions, when both task modification and timed performance are likely to change. Alternatively, we used a simple solution for combining timed performance and task modification by multiplying the MOD score by the time required to complete the task. This method increased the variation tremendously, but may allow for a more sensitive measurement of overall physical function. When compared to the MOD score and timed performance, the combination score was similarly related to common measures of function and physiological impairment.

The MOD score is appealing because of its intuitive meaning (higher score = more modification), simplicity of use, and easy incorporation into any setting. For example, testing requires three chairs with armrests (seat pan of 43 cm, 38 cm, and 30 cm), a carpeted floor, and a flight of stairs (10 steps) with a handrail. Although the scores can be used for individual tasks, it is recommended to calculate a summary score. The summary score creates a semicontinuous measure of modification and reflects physical ability across simple (43 cm chair rise), moderately challenging (stair climb), and demanding tasks (supine and kneel rises).

There are several limitations that need to be noted. First, the MOD score represents the most common observed modifications, and we do not claim to have documented all that may exist. Furthermore, the MOD score was only developed using lower extremity tasks. The score also introduces subjectivity, but this error is extremely low when using the summed score. Some scores were not represented by our sample (brushing the handrail on the stair ascent), but because others have documented them to occur (3), we decided to include them in the scale. Additionally, no one refused or needed assistance with the 43 cm or 38 cm chair rise or the stair ascent/descent task, but we included this category to help capture lower functioning older adults. Another limitation is that we recruited a convenience sample of community-dwelling older adults who self-reported some or a lot of difficulty performing a chair rise or stair climb; this recruitment strategy causes obvious limitations in applicability with population-based samples. The applicability in those persons who are dependent in activities of daily living has yet to be determined, but because the scale offers categories for refusal and needing assistance, it is thought to be robust even in frail older adults. High functioning older adults are likely to show a ceiling effect (similar to when using other measures), but this effect is minimized by including challenging tasks. Nevertheless, future research is needed to determine the applicability in more disabled and high functioning older adults.

This study expands on previous work done with self-reported measures of task modification. The most important finding here, that has not been previously demonstrated, is that a semicontinuous objective measure of task modification is reliable and is associated with physiological impairment and functional limitation in older adults regardless of timed performance. This is the first step in the recognition, development, and standardization of an objectively measured task modification scale that may be used to quantify physical ability at an intermediary step prior to disability. Future directions for the MOD score include comparison with varying disability levels (Community vs Congregate housing dwellers), use as an outcome measure during an intervention, and development of a survey version.


   Acknowledgments
Top
 Abstract
 Methods
 Results
 Discussion
 References
 
This work was supported by a student research award (American College of Sports Medicine and Kirby Foundation), by a Michael Pollack Memorial Grant from the Life Fitness Academy, and by The Syracuse University Graduate School.


   Footnotes
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 Abstract
 Methods
 Results
 Discussion
 References
 
Decision Editor: Luigi Ferrucci, MD, PhD

Received June 7, 2005

Accepted September 19, 2005


   References
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 Abstract
 Methods
 Results
 Discussion
 References
 

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