Muscle Strength as a Predictor of Gait Variability after Two Years in Community-Living Older Adults.

BACKGROUND: Stride-to-stride fluctuations, or gait variability, can be captured easily using body worn inertial sensors. Previously, sensor-measured gait variability has been found to be associated with fall risk and central nervous changes. However, further research is needed to clarify the clinical relevance of this method. OBJECTIVES: In this study, we look at how gait variability is associated with muscle strength, measured two years earlier. DESIGN, SETTING AND PARTICIPANTS: This is study of longitudinal associations. Participants were community-dwelling volunteers between 70-81 years. MEASUREMENTS: Participants were tested while walking with a single sensor at their lower back, and they walked back and forth over a distance of 6.5 meters under four conditions: at preferred speed, at fast speed, with an added cognitive task, and while walking across an uneven surface. Gait variability in the anteroposterior (AP), mediolateral (ML) and vertical (V) directions was identified. A muscle strength score was composed by transforming hand grip strength, isometric knee extension strength and the 30 second chair rise-test to z-scores and adding them. RESULTS: 56 individuals were analysed (mean age at baseline 75.8 (SD 3.43), 60 percent women). In a backwards regression method using age, gender and baseline walking speed as covariates, muscle strength predicted gait variability after two years for AP variability during preferred speed (Beta= .314, p=.025) and uneven surface walking (Beta=.326, p=.018). Further, muscle strength was associated with ML variability during preferred speed (Beta=.364, p=.048) and fast speed (Beta=.419, p=.042), and V variability during preferred speed (Beta=.402, p=.002), fast speed (Beta=.394, p=.004) and uneven surface walking (Beta=.369, p=.004). CONCLUSIONS: Sensor-measured gait variability tended to be associated with muscle strength measured two years earlier. This finding could emphasize the relevance of this relatively novel measure of gait in older adults for both research and clinical practice.

The Association between Daily Walking Behavior and Self-Reported Physical Function in Community-Dwelling Older Adults.

Many older people do not participate in organized exercise, and daily walking may be the most substantial contributor to physical activity. To investigate the association between daily walking behavior and self-reported health-related physical function, older community-dwelling volunteers wore activity-registering sensors for three days. Self-reported health-related physical functioning was measured using the SF36 10-item Physical Function subscale. Forty-six participants wore a sensor (mean age 77.6, SD 3.6, 61 % women). In a multiple regression model, steps per day (B=.005, p≤.001) and walks per day (B=-.174, p=.010) were associated with the SF36-PF subscale. The association between physical functioning and walks per day was negative: Those who took many walks per day may have been walking more indoors. Health professionals are likely justified in advising older people to incorporate walking into daily life for health purposes. The cross-sectional design does not allow for inferences about causality.

Test-retest reliability of trunk accelerometric gait analysis.

The purpose of this study was to determine the test-retest reliability of a trunk accelerometric gait analysis in healthy subjects. Accelerations were measured during walking using a triaxial accelerometer mounted on the lumbar spine of the subjects. Six men and 14 women (mean age 35.2; range 18-57) underwent the same protocol on 2 consecutive days. The raw acceleration signals from six self-selected walking speeds were transformed into a horizontal-vertical coordinate system to remove unwanted variability caused by gravity. Acceleration root mean square values, cadences, step and stride lengths were then computed and interpolated using quadratic curve fits and point estimates were calculated at a standardised walking speed of 1.35 m/s. Relative reliability was determined using two models of intraclass correlation coefficients (ICC(1,1) and ICC(3,1)) to assess any systematic shifts and absolute reliability was determined using measurement error (ME). The results of the study showed high ICC values (0.77-0.96) and ME values of 0.007-0.01 g for mean acceleration; 0.009 m for step lengths; 0.022 m for stride length and 1.644 step/min for cadences. In conclusion, the method was found to be reliable and may have a definite potential in clinical gait analysis.

Assessment of adaptive walking performance.

Although mostly negative aspects are reported to be associated with gait variability, irregular walking is needed when walking performance has to be adapted to specific environmental conditions. The aim of this study was to evaluate the test-retest reliability and discriminative ability of a measure to assess adaptive walking performance and to identify parameters associated with test performance in young and elderly subjects. Eighteen older (mean age 78.1 years) and 19 young women (mean age 30.8 years) were instructed to walk as precisely as possible over a defined course targeting 26 arbitrarily positioned rectangle boxes fixed on an instrumented walk way with embedded pressure sensors. ICC(1,1) of 0.79 demonstrated sufficient reliability in the cohort of older women. Targeting was significantly worse (or deviation was larger) in older women than in young women (mean 3.20cm versus 2.27cm, p=0.005). Mean gait speed of the older women was higher during the test (0.50m/s versus 0.40m/s, p=0.020), but not during unconstrained walking (1.15m/s versus 1.50m/s, p<0.001). The deviation measure classified 78% of the subjects into correct age group (sensitivity 67%, specificity 90%, p=0.003). Adaptive walking performance was associated with parameters describing physical performance as well as with cognitive executive function. This study shows that this test of adaptive walking performance is a reliable measure of irregular walking with ability to discriminate between young and older subjects. Our results suggest that older persons might try to camouflage their lack of accuracy during adaptive walking by higher gait speed.

Measurement properties of the Non-Communicating Adult Pain Checklist (NCAPC): a pain scale for adults with Intellectual and Developmental Disabilities, scored in a clinical setting.

The 18 items' Non-Communicating Adult Pain Checklist (NCAPC) has been developed from the 27 items Non-Communicating Children Pain Checklist to better capture pain behavior of adults with Intellectual and Developmental Disabilities (IDD). As part of the NCAPC's measurement properties, internal consistency, reliability and sensitivity to pain have been evaluated and found satisfactory, using scores based on video-uptakes. The aim of the article therefore was to examine the instrument's discriminative ability and sensitivity to pain of adults at different levels of IDD when scored within a clinical situation as well as through video-uptakes. Participants were 59 adults at different levels of IDD who were observed for pain behavior, before and during dental hygiene treatment (scored directly) and influenza injection (scored from video-uptakes), using the NCAPC. The results suggest that the NCAPC differentiated between pain and non-pain situations, as well as between pain reaction during two different medical procedures expected to cause more or less pain, and it was found sensitive to pain at all levels of IDD. We conclude that the present findings add to previous findings of measurement properties of the NCAPC, and support that it can be scored directly in a clinical setting.

Changes in step-width during dual-task walking predicts falls.

The aim was to evaluate whether gait pattern changes between single- and dual-task conditions were associated with risk of falling in older people. Dual-task cost (DTC) of 230 community living, physically independent people, 75 years or older, was determined with an electronic walkway. Participants were followed up each month for 1 year to record falls. Mean and variability measures of gait characteristics for 5 dual-task conditions were compared to single-task walking for each participant. Almost half (48%) of the participants fell at least once during follow-up. Risk of falling increased in individuals where DTC for performing a subtraction task demonstrated change in mean step-width compared to single-task walking. Risk of falling decreased in individuals where DTC for carrying a cup and saucer demonstrated change compared to single-task walking in mean step-width, mean step-time, and step-length variability. Degree of change in gait characteristics related to a change in risk of falling differed between measures. Prognostic guidance for fall risk was found for the above DTCs in mean step-width with a negative likelihood ratio of 0.5 and a positive likelihood ratio of 2.3, respectively. Findings suggest that changes in step-width, step-time, and step-length with dual tasking may be related to future risk of falling. Depending on the nature of the second task, DTC may indicate either an increased risk of falling, or a protective strategy to avoid falling.

Gait patterns in subjects with rheumatoid arthritis cannot be explained by reduced speed alone.

The aim of this study was to investigate the characteristics of gait in subjects with rheumatoid arthritis (RA) by comparing gait parameters obtained from these subjects and controls. Seventeen subjects with RA in functional class II (mean age 51.1 years, S.D. 6.2 years) and 20 controls (mean age 50.4 years, S.D. 5.3 years) were instructed to walk a straight walkway at five different self-selected speeds. Speed-dependent variables were analysed by an interpolation procedure to estimate scores at a normalized speed of 0.8m/s. At self-selected speed the RA group walked significantly slower, with a shorter step length and longer stance phase. There was no difference in cadence and step width. When controlling for speed, the RA group walked with shorter step length (p=0.04) and higher cadence (p=0.03) compared to controls, but no significant difference in stand phase and step width was found. The present study demonstrates that speed-dependent gait variables are affected when controlling for the effect of speed in subjects with RA. In further studies of gait, speed should be controlled for.

Reliability of the Non-Communicating Adult Pain Checklist (NCAPC), assessed by different groups of health workers.

Evaluating pain in adults with intellectual and developmental disability (IDD) is a challenge. The Non-Communicating Adults Pain Checklist (NCAPC) was recently developed from the Non-Communicating Children's Pain Checklist (NCCPC) and examined in a group of adults with IDD (N=228) and found to hold satisfactory construct validity, internal consistency and sensitivity to pain. To further explore its basis for clinical use, intra and interrater reliability of the NCAPC was investigated. Data collection was done by videotaping the participants before and during influenza vaccination. Intrarater reliability was evaluated by the first author on a group of 50 randomly selected individuals (mean age 42.5, range 19-72) and was found at 0.94. Interrater reliability was investigated in two stages. In the initial step different groups of health care workers (caregivers, nurses, case managers, and therapists), each including five raters, viewed a sample of 12 adult participants with IDD (3 at each level of IDD mean age was 49 years, range 16-72), that were extracted from the population sample. Interrater reliability of all raters within the groups varied from low to very high (ICC(1,1)=0.40-0.88). Interrater reliability was very high in caregivers. The Physical -and Occupational therapists are one group were considered potential users of the measure. In the second stage 3 participants from each of the groups showing high interrater reliability (caregivers and therapist) evaluated interrater reliability in a randomly selected group of 40 individuals (mean age 41.2, range 15-72). Interrarter reliability for the therapists and caregivers was found at 0.91 and 0.92 correspondingly. The researchers conclude that that the NCAPC have been found to hold high reliability values.

Test-retest reliability of trunk accelerometry during standing and walking.

OBJECTIVE: To investigate repeatability of acceleration measured by a portable, triaxial accelerometer over the lumbar spine as a measure of balance during standing and walking. DESIGN: Acceleration was measured along three axes and transformed to a horizontal-vertical coordinate system. Standing was tested on two feet, vision unobstructed and obstructed, and on one foot, vision unobstructed. Walking was tested in five different self-selected speeds on even and uneven ground. Retest was performed after 2 days. SETTING: A flat floor with a 7m uneven mat. SUBJECTS: Nineteen healthy students. MAIN OUTCOME MEASURES: Standing: Acceleration root mean square (RMS). Walking: Point estimate of acceleration RMS for a reference walking speed (1.2m/sec). All tests: Within-subject standard deviation (sw), intraclass correlation coefficients (ICCs). RESULTS: The sw indicated high absolute test-retest repeatability for standing on two feet. Because of restricted ranges of value, relative reliability was low, however, with ICC(3,1) < .56. For standing on one foot, absolute and relative reliability were highest in the mediolateral direction, with ICC(3,1) = .84. For the walking tests, ICC(3,1) ranged from .79 to .94 for the three axes. Reliability was on the same level for even and uneven ground. CONCLUSION: The results indicate that accelerometry without need for stationary instrumentation is a reliable method that may be useful for studying standing balance and gait in the clinic.

A new method for evaluating motor control in gait under real-life environmental conditions. Part 1: The instrument.

OBJECTIVE: To devise an instrument to measure linear acceleration of the trunk during gait under real-life environmental conditions. DESIGN: A mathematical algorithm is suggested to transform data to a horizontal-vertical coordinate system. Calibration procedures are described. BACKGROUND: A portable, low mass device to measure linear acceleration of the trunk in a horizontal-vertical coordinate system during prolonged walking is of clinical interest and has not been described previously. METHOD: Linear acceleration is registered by a triaxial, piezoresitant accelerometer, sampled at 512 Hz and collected by exchangeable 20 Mb memory cards of a body-mounted data-logger. Data are transformed to a horizontal-vertical coordinate system, utilising the accelerometer's capacity as an inclinometer. Calibration testing was done in a servohydraulic jig by measuring acceleration of 5 Hz, 16 mm vertical displacements, first along each of the sensing axis, then by a tilted accelerometer. RESULTS: Precision testing of each axis and transformed data from all axes showed low variability for acceleration root mean square of sequences of 1000 samples (CV <0.001). Accuracy testing by double integration of transformed data from the tilted accelerometer demonstrated a mean absolute difference of 0.04 mm (SD = 0.03 mm) from the programmed input. CONCLUSIONS: Data from the arbitrarily tilted accelerometer transformed to a horizontal-vertical coordinate system gave precise and accurate measurements of linear accelerations when tested in a servohydraulic jig. Procedures for applying the device in gait analysis are described in a companion article. RELEVANCE: Control of upper body and body centre of mass are important aspects of balance, but gait analysis has largely focused on the movements of the lower limbs. This device can be used to register acceleration of a reference point on the upper body during walking, and may thus give new information about balance in gait.

A new method for evaluating motor control in gait under real-life environmental conditions. Part 2: Gait analysis.

OBJECTIVE: The validity of assessing balance in gait by measuring balance in standing is questionable. Better methods for measuring balance during walking are therefore needed. DESIGN: It is suggested that the individual will demonstrate adequate postural control by moving a reference point near the body centre of mass (CoM) smoothly towards an intentional goal, even though movements of the extremities show variability consistent with a changing environment. BACKGROUND: In spite of an increased interest in variability as a prerequisite for motor control, gait analysis methods focus, to a large extent, on symmetry and repeatability of movements in stereotyped settings. METHODS: Acceleration of a reference point over the lumbar spine is registered during walking by a portable, triaxial accelerometry system. RESULTS: A quadratic relation between acceleration root mean square (RMS) and walking speed is demonstrated, and a second degree polynomial can therefore be computed as a curve estimate, if acceleration RMS representing at least three walking speeds are available. CONCLUSIONS: The relation between acceleration over a reference point on the trunk and walking speed can be compared between trials and also when walking speeds are self-selected. Calibration procedures and testing of the instrument for precision and accuracy in a mechanical testing jig are described in a companion article. RELEVANCE: This study suggests a new alternative to the traditions of measuring balance in standing and movements of the legs in walking. The method allows balance in gait to be assessed at self-selected speeds in relevant environmental conditions, which may facilitate gait analysis in the clinic and improve the validity of the results.