The assessment of functional limitation is the third diagnostic criteria for sarcopenia after the assessment of muscle mass and strength. Functional limitations refer to an individual's physical or mental capability without reference to the social context.1 A gait speed of 0.8 to 1.0 m/s has been suggested as a criterion for identifying those at risk of sarcopenia.2 , 3 Gait speed (8 ft), the ability to rise from a chair (5 times), and balance tests (semitandem and tandem stands) have been included in the Short Physical Performance Battery (SPPB), which has been validated in older adults and found to predict nursing home admission.4 Furthermore, older adult performance on the SPPB or tests of similar difficulty has been associated with laboratory measures of muscle mass and function. Low relative skeletal mass has been shown to be associated with performance on the SPPB.5 Increasing knee extensor (KE) strength has been associated with improved walking speed and the ability to rise from a chair,6 , 7 and increasing KE power has been linked to improved self-reported8 and objectively measured (SPPB; stair climbing) physical performance.9
Functional performance measures such as those within the SPPB or similar tests such as gait speed tests of 10 m or less and chair rise tests of 5 repetitions or less have primarily been used to assess functional limitation in frail older adults older than 65 years10–12 up to and including 95 years.8 However, changes in muscle quality, which precede functional limitation, become noticeably different to a young adult at the beginning of the sixth decade.13–18 Comparatively, there are limited data on the functional capability of healthy older adults and consequently, little is known about the time course and transition to a reduction in functional capability in those prior to 65 years. Reductions in aerobic capacity and muscle function are inevitable even in masters athletes,19 , 20 but tracking age-related difference in functional capability among healthy older adults provides a challenge due to the heterogeneity of their functional capabilities. Ideally, functional performance measures would be related to the performance of activities of daily living but also able to distinguish meaningful gradations of functional capability and change over a wide range of abilities.
Test batteries such as the SPPB may suffer from a ceiling effect when used in healthy cohorts.21 A healthy older adult may perform short gait speed or chair rise tests in a similar manner to a young adult, meaning the tests cannot detect change where expected. One option to combat this effect is to use extended tests of chair rise ability or gait speed. This may allow participants to perform to a greater physiological maximum and therefore distinguish more subtle gradations of capacity in healthy adults. Some authors22 , 23 have proposed extended tests such as the 30-second chair stand test and the 6-minute walk test23 , 24 as a method to combat the floor effect, that is where an older adult may not be able to complete a fixed distance or number of chair rises. Tests of this nature may also have the potential to derive meaningful performance data for healthy older adults.
Although test-retest reliability for gait speed and chair rise tests has previously been described in those 60 years of age or older,23–27 it has not been described in healthy adults 50 years of age or older. Furthermore, a learning effect has been reported during the measurement of voluntary strength in healthy adults naïve to a laboratory environment.28 Investigations into whether a learning effect exists in the measurement of functional performance are required to ensure criterion validity of the data reported. Assuming reliable measures of functional performance can be determined, it remains to be observed whether gait speed tests of 10 m or less and chair rise tests of 5 repetitions or less can detect age-related difference in the functional capability of healthy older adults. Furthermore, it remains to be observed whether extended tests of functional performance offer greater sensitivity in detecting age-related change in functional capacity. Finally, given the association between strength and functional performance in older adults29–32 and the fact that strength at a single time point is predictive of future mobility limitation,33 it is important to determine whether there is an association between short or extended functional performance tests and laboratory measures of lower extremity muscle strength in healthy adults between 50 and 70 years of age. The purpose of this study was to (a) determine test-retest reliability of functional performance using short (10-m gait velocity, 5 chair stands) and extended (900-m gait velocity and the number of chair stands in 30 seconds) tests, (b) determine the efficacy of short and extended tests of functional performance in detecting age-related difference between the sixth and seventh decades in healthy older adults, and (c) examine the association between maximal voluntary isometric torque of the KEs and performance in short or extended tests of functional capability in the same sample.
A convenience sample (n = 204) of healthy older (50-70 years) adults was recruited via e-mail and word of mouth from the University of Limerick campus community and surrounding area to take part in the University of Limerick Healthy Aging Study.28 , 34 , 35 For the present investigation, 159 older adults, mean age (standard deviation) of 60.4 (5.3) years, from the sample volunteered to participate; 18.2% (n = 29) were men. There were 11 (15.5%) and 18 (11.3%) men in the 50- to 59-year and 60- to 70-year age brackets, respectively. Participants received a full medical screening and physical examination prior to the assessment of a maximal voluntary contraction (MVC) and functional performance. Those defined as healthy, that is, disease-free based on Greig et al36 and living independently were invited to participate. Disease-free included the absence of clinical, cardiovascular, or musculoskeletal abnormality as determined by a medical doctor. Participants were required to be healthy but not masters athletes. After receiving a complete explanation of the procedures, benefits, and risks of the study, all participants gave their written informed consent. Testing was carried out between January 2011 and May 2013. This study was approved by the Research Ethics Committee of the University of Limerick (EHSREC 10-RA03).
Participants presented to the laboratory in a tracksuit or comfortable clothing suitable for exercise. Participants were tested during 2 identical sessions held 7 days apart, at the same time of the day to reduce the potential for a learning effect previously identified in the measurement of strength in this population.28 All measurements were carried out by the same exercise scientist, who was blind to age, to exclude issues with intertester reliability and reduce risk of bias. Warm-up consisted of 5 minutes on a bicycle ergometer (Monark Ergomedic, Monark, Sweden; 828E) at an intensity of 40 W. The entire sample (n = 159) completed an MVC, a 5 repetition chair rise test and an extended 900-m gait speed test. A smaller proportion of the sample (n = 65/159) completed 10-m gait speed tests due to preliminary analysis, which suggested that the tests could not detect age-related difference in gait speed where expected. The 30-second chair rise test was added to the University of Limerick Healthy Aging Study at the midway point and therefore also has a smaller sample size (n = 91/159).
Maximal Voluntary KE Strength Measurements
Maximal voluntary isometric contractions of the KEs of the dominant limb (limb used to kick a ball) were measured using a Con-Trex MJ Dynamometer (Con-Trex MJ; CMV AG, Dubendorf, Switzerland). Peak isometric torque was measured in Newton meters. Participants were seated with a hip flexion angle of 70°. The back of the knee joint was on the edge of the seat with a knee angle of 60° from anatomical zero (0°). The distal shin pad of the dynamometer was attached 4 to 5 cm proximal to the medial malleolus using a Velcro strap. The dynamometer rotational axis was aligned with the lateral femoral condyle (knee joint axis of rotation). Participants were instructed to perform 2 submaximal voluntary isometric contractions (50% and 75% of perceived maximum) prior to each test series as in the study by Maffiuletti et al,37 with a 1-minute rest period in between. The participants then performed 3 MVCs of the KEs separated by 2 minutes of rest. An MVC produced a measure of isometric peak torque (PT) in a single effort that required greater than 200 ms and was sustained for at least 250 ms. Disqualification of an MVC from further analysis was based on the following criteria: (a) an attempt not sustained for MVC, identified by an impact spike prior to 300 ms; (b) an attempt containing an initial countermovement, identified by a visible drop/rise in the torque signal greater than 5 N·m; or (c) an attempt with a nonlinear time-torque trace, identified by a double movement. Repeated PT values within a coefficient of variance of 5% that satisfied the criteria for MVC were accepted for analysis. A detailed breakdown of the strength assessment procedures including within and between day reliability is available in our recently published article.28
Ten-Meter Gait Speed Tests
Gait speed was assessed using timing gates (Micro-Gate, Polifemo, Bolzano, Italy) separated by 1.5 m positioned at 0 and 10 m of a measured walkway. Participants stood at the beginning of a track marked by a white line and from a static start were instructed to walk at their “normal” pace to assess habitual gait speed. Participants were instructed to walk as fast as they could without running in the case of maximal gait speed. Participants had an open walkway for deceleration. Each trial condition was repeated twice.
Chair Rise Tests
The ability to rise from a chair was assessed using a chair, 44 cm from the floor, which was placed against a wall for support. Participants were instructed to sit upright away from the back rest of the chair with their arms crossed against their chest. Participants were asked to perform 1 full chair stand before completing the test in order for them to establish a preferred foot position. Participants began the test from a seated position and were asked to complete 5 chair rises as fast as possible. Participants were informed that only chair rises in which they reached full extension from the seated position would be counted. The exercise scientist held the watch and communicated only verbally with the instructions “Go” and “Stop” at the beginning and end of the test. Subsequently, with no defined rest period, using the same positioning and technique, participants were instructed to perform as many chair rises as possible in a 30-second time period. The 5 repetition chair rise test always preceded the 30-second chair rise test. Each test was performed once on each of the 2 test days.
Extended Gait Speed Test
Extended gait speed was assessed using a timed 900-m test. Participants were brought to an indoor track that measured 225 m per lap. Participants were instructed to complete 4 laps of the track as fast as they possibly could. The majority of participants used 1 or a combination of running, jogging, or walking to complete the test. No instruction was provided as to correct pacing but tests were performed twice separated by 7 days to ensure adequate habituation to the test had taken place. The purpose of this test was to allow participants to perform to a greater physiological maximum than allowed by the 10-m tests.
The data were analyzed using SPSS 22.0 for Windows (SPSS, Inc, Chicago, Illinois). A 2-way mixed-model intraclass correlation coefficient was used to assess absolute agreement as it indicates the error in measurements as a proportion of total variance in measures. Cross-tabulation was used to determine the proportion of males and females in the respective age categories. Pearson χ2 test was used to determine whether differences in the proportions of males between groups were statistically different. The difference in functional performance between test days was reported using a paired sample t test. To report descriptive statistics for PT and functional performance, a Kolmogorov-Smirnov or Shapiro-Wilk test was conducted to determine normality. Mean and standard deviation, median and interquartile range, and 95% or boostrap 95% confidence intervals (CIs) are reported. Cross-sectional age or gender-related difference in PT and functional performance were analyzed using an independent samples t test or a Wilcoxon signed rank test for normal and nonnormal data, respectively. Pearson r was used to report the association between PT and functional performance. Simple linear regression analysis was used to assess the variance in functional performance accounted for by KE PT (Figure 1). Removal of outliers visible on the scatter plot did not alter the statistical significance or category of association and therefore they were not removed. Stepwise linear regression was used to assess whether sex or body mass index affected associations between PT and functional performance for the sample as a whole and separated by age categories. Functional capability (gait speed or chair rise) was entered as the dependent variable and PT, sex (1 = female, 2 = male), and body mass index were entered as independent variables.
Table 1 displays physical characteristics for the 159 healthy adults between 50 and 70 years of age who participated in this study. Physical characteristics are presented separately for those in the sixth (n = 71) and seventh (n = 88) decades of life. The proportion of men and women in the sixth (15.5% and 84.5%, respectively) and seventh decades (20.5% and 79.5%, respectively) was not statistically different (P = .421). Knee extensor torque and 900-m gait speed were the only measures where performance between men and women differed (P < .05).
Reliability of Estimate
Our functional performance measures included habitual and maximal 10-m gait speed, 5 repetition and 30-second chair stand performance, and 900-m gait speed. Test-retest reliability, for the assessment of all functional performance measures tested on 2 separate occasions separated by 7 days, is displayed in Table 2. Reliability was affected by a learning effect between test days that led to a statistically significant increase in performance (P < .05) on day 2. The 900-m test was the only measure of functional performance not previously used in the literature but demonstrated the highest intraclass correlation coefficient (0.880; 95% CI, 0.811-0.925). Age-related difference in measures of functional performance and associations with KE-PT are reported from the highest values recorded from both days.
Age-Related Difference in Functional Performance
Table 3 displays age-related difference in functional performance. Ten-meter habitual (P = .095) and maximal (P = .856) gait speed were not different between those in the sixth and seventh decades. Both 5 repetition (8.2 [2.6] seconds vs 8.8 [2.5] seconds; P = .006) and 30-second (16.5  vs 14.0 ; P = .028) chair rise tests were lower for those in the seventh decade. Those in the seventh decade had an 11.3% (0.29 m/s; 95% CI, 0.12-0.46; P = .001) lower gait speed when completing 900 m compared with those in the sixth decade.
The Association Between Lower Extremity Strength and Functional Performance
Peak torque normalized for body mass was 14.2% (0.2 N·m/kg; CI, 0.08-0.33; P = .001) lower for older adults in the seventh decade of life compared with their young counterparts in the sixth decade. Other than 900-m performance, all measures of functional performance had a weak (r = 0.226-0.360; P < .05) association with KE-PT (Table 4). Performance in the 900-m gait speed test had a moderate association (r = 0.537; P < .001) with KE-PT. Sex and body mass index did not have a statistically significant effect on associations between KE-PT and functional performance (P > .05).
Repeated measurement of functional performance separated by 7 days revealed a statistically significant learning effect in the form of a performance improvement on day 2 (P < .05). These findings highlight the importance of the need to reduce the learning effect observed with performance tests in healthy older adults. Neither habitual nor maximal 10-m gait speed could determine age-related difference in functional capacity, in essence confirming our hypothesis that shorter gait speed tests may suffer from a ceiling effect in the assessment of healthy older adults. The 900-m extended gait speed test highlighted an 11.3% difference in performance between those in the sixth and seventh decades of life. Both short and extended chair rise tests were capable of detecting age-related difference in muscular power and endurance, respectively. The chair rise and extended gait speed tests confirm that tests centered on lower extremity power and/or tests that allow performance to a greater maximum can effectively combat the ceiling effect evident with use of short gait speed tests in healthy older adults. All measures of functional performance had a weak to moderate association (r = 0.226-0.534; P < .05) with KE strength.
Diagnostic criterion for sarcopenia is considered to be a gait speed of less than 0.8 to 1.0 m/s.2 , 3 The mean habitual gait speed in the present investigation was 1.5 m/s, which demonstrates the relative health of our sample in comparison to a cohort with sarcopenia. It is, therefore, somewhat unsurprising that neither 10-m habitual nor maximal gait speed test was capable of detecting age-related difference between the sixth and seventh decades. Glenn et al21 provide support for these findings in a sample of similar age (61.5 years), size (n = 102), and habitual gait speed (1.44 m/s). The authors report no difference in habitual gait speed between older adults who are sedentary, recreationally active, or masters athletes, and no difference in maximal gait speed between those who are sedentary or recreationally active. However, our results must be interpreted in light of the small number of participants who completed 10-m gait speed tests in the 50- to 59-year (n = 37) and 60- to 70-year (n = 28) age brackets, respectively. In the present study, the extended gait speed test revealed differences in functional capacity where expected between the sixth (n = 71) and seventh decades (n = 88). In addition to its construct validity, this test demonstrated high reliability and has been reported to be sensitive to change during a short-term (12 weeks) resistance training intervention.35 We report an 11.3% difference in gait speed between the sixth and seventh decades (2.56 m/s vs 2.27 m/s; P = .001), which is similar to the 11.3% (1.53 m/s vs 1.35 m/s) difference reported by Rikli and Jones38 between the seventh and eighth decades. Although this appears to suggest a similar per decade decline between the sixth and seventh decades, it must be acknowledged that there are differences in test administration such as our test was of fixed distance, and participants were allowed to run compared with the 6-minute walk test, which is not of fixed distance and requires participants to remain walking. There is potential in our test that the mean gait speed could be inflated or underestimated by the number of participants choosing to run or walk. Despite these differences, both tests allow participants to perform to the maximum of their ability for an extended distance (400-900 m) or duration (6-6.5 minutes), and, therefore, relative differences in performance can be compared with caution.
Chair Rise Tests
Participants in the seventh decade of the present study performed approximately 2 fewer chair rises than those in the sixth decade (14  vs 16.4 [3.5]; P = .028) in a 30-second time period. The 14 chair rises performed by those in the seventh decade is comparable with the 14.3 chair rises for those in the seventh decade reported by Rikli and Jones38 and represents a 13.3% to 14.5% difference between the sixth and seventh decades. Our results, therefore, help extend the work of Rikli and Jones32 in the seventh, eighth, and ninth decades by providing values, albeit in a smaller sample, for the sixth decade of life. The finding of a detectable difference in 5 repetition chair rise performance (8.2 [2.6] seconds vs 8.8 [2.5] seconds; P = .008) between decades might not have been expected because of our hypothesis that shorter tests would suffer from a ceiling effect. It may be that as the 5 repetition chair rise test is a test of lower extremity power, the difference more closely represents the observed difference in KE-PT normalized for body mass (1.48 [0.45] N·m/kg vs 1.27 [0.34] N·m/kg; P = .001). These explanations must be interpreted while being aware that the observed change (7.3%) in 5 repetition chair rise performance between decades is similar to the coefficient of variance (7%) for repeated measures between test days.
Knee Extensor Strength and Functional Performance
Knee extensor strength was 14% lower for those in the seventh decade, a finding consistent with the 8% to 15% per decade change in strength reported in adults between 40 and 70 years of age.28 , 39 , 40 Knee extensor strength explained 10% of the variance or greater in maximal 10-m gait speed, 5 repetition chair rise test, and 30-second chair rise test (Figure 1) but 29% of the variance in extended gait speed. Buchner et al41 reported 17% of the variance in gait speed (15.2 m) to be explained by lower limb strength (knee extensor and flexor, ankle plantar and dorsi flexors) in 60- to 96-year-old men and women. Ostchega et al6 reported 20% of the variance in 6-m gait speed to be explained by KE-PT in adults 50 years of age or older. However, comparisons are limited both in test duration and population sampled. To the authors' knowledge, the timed 900-m test is the first extended gait speed assessment in which more than 25% of the variance can be explained by lower extremity strength in healthy older adults. This is a large proportion of the variance considering that endurance performance is also dependent upon cardiorespiratory capacity and peripheral muscular adaptations such as capillary and mitochondrial density. The fact that increasing gait speed is associated with increasing muscle strength during a test with a gait speed range of 1.3 m/s to 4.3 m/s is encouraging. This means the relative muscular effort for those with the mean gait speed (2.27 m/s-2.56 m/s) is considerably less when walking at a normal healthy gait speed (1.5 m/s) for an extended period of time. A reduction in the relative effort required to perform activities of daily living has important implications toward the goal of prolonging independent living and quality of life.
Our findings are limited to a relatively small (n = 159) convenience sample of healthy older adults from the university campus community and surrounding areas. Furthermore, when comparing the findings of short and extended performance tests, it should be noted that while all participants (n = 159) had a measure of strength, 5 repetition chair rise time and 900-m gait speed, less than half (n = 65) had a measure of 10-m gait speed. Despite the 900-m gait speed test being sensitive to age-related difference in functional performance and having the strongest association with lower extremity strength, the lack of control over the number of participants walking, jogging, or running may have over- or underestimated our gait speed and, therefore, influenced the strength of the associations reported. Our strength measures are normalized to body mass and not the relevant segment of thigh lean tissue or skeletal mass that was measured by the dynamometer, which may alter the association seen in the present study. It remains to be seen whether strength normalized for body mass or strength per unit skeletal or lean tissue (muscle quality) has a stronger association with functional performance. We did not assess participants for stage of the menopause, cognitive function, or depression, nor did we control for habitual physical activity; therefore, it is unknown how these cofounding variables may have affected our results. Finally, education and socioeconomic status have been reported to influence the health of a population,42 we have not controlled for this, and our sample may be subject to a greater health bias due to being recruited from a university campus community.
The majority of functional performance tests (4/5) used in this investigation demonstrated a learning effect evidenced by a performance improvement on day 2 of assessment. This investigation demonstrated 10-m gait speed tests not to have the sensitivity to report age-related difference in the functional capacity of healthy older adults. The extended tests in this investigation demonstrated construct validity by being able to distinguish differences in functional performance between healthy adults in the sixth and seventh decades of life. The 900-m gait speed test also had a greater association with KE strength than previous gait speed associations reported in the literature. Future research should seek to determine (a) whether the observed learning effect in the assessment of functional capability is attenuated after a third test day and (b) what the relative contributions of muscle mass, strength, and quality (strength per unit tissue) are to functional capability in healthy older adults.
The authors thank the University of Limerick for funding this study, speciﬁcally the “Road-bridge Medical Research Scholarship,” which funded the authors PhD research. This study was also supported by Food for Health Ireland and Enterprise Ireland grant CC20080001.
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