Rolf Moe-Nilssen

Estimation of gait cycle characteristics by trunk accelerometry

This study reports on the novel use of a portable system to measure gait cycle parameters. Measurements were made by a triaxial accelerometer over the lower trunk during timed walking over a range of self-administered speeds. Signals from each trial were transformed to a horizontal-vertical coordinate system and analyzed by an unbiased autocorrelation procedure to obtain cadence, step length, and measures of gait regularity and symmetry. By curvilinear interpolation, speed-dependent gait parameters could be compared at a normalized speed. It was demonstrated that analysis of gait cycle parameters which previously required fixed laboratory equipment and paced walking procedures, now can be made from data obtained by a timing device and a portable sensor at free walking speeds.

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.

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.

Trunk accelerometry as a measure of balance control during quiet standing

The goal was to investigate whether body sway measured by trunk accelerometry during quiet standing could differentiate between young and elderly healthy subjects, and between conditions with eyes open and closed on firm and compliant surfaces. Raw data demonstrated poor discrimination, but horizontal transformation to eliminate a constant gravity component disclosed consistent mean differences across groups (P < or = 0.0025), and also between conditions (P < or = 0.0005), except for the most marginal difference. When drift associated with very low frequency body sway was adjusted for, a significant difference appeared also here (P = 0.001). This study indicates that trunk accelerometry can discriminate between populations and conditions during quiet standing.

The effect of gait speed on lateral balance control during walking in healthy elderly

The aim of this paper was to investigate the effect of speed dependency on lateral gait parameters. In 36 healthy elderly (mean age=72.5 years, S.D.=3.2 years), walking at four different self-administered speeds, mediolateral trunk acceleration and step width (SW), but not step-width variability (SWV), were found to have quadratic relations to gait speed. Normalizing for speed by curvilinear interpolation, and controlling for subject characteristics, disclosed smaller SW (adjusted R2=0.41, P<0.001), but larger SWV (adjusted R2=0.26, P=0.01) with increasing age in multiple regression models. These relations were camouflaged at preferred speed.

Does walking strategy in older people change as a function of walking distance

This study investigates whether the spatio-temporal parameters of gait in the elderly vary as a function of walking distance. The gait pattern of older subjects (n=27) over both short (SWD<10 m) and long (LWD>20 m) walking was evaluated using an ambulatory device consisting of body-worn sensors (Physilog). The stride velocity (SV), gait cycle time (GCT), and inter-cycle variability of each parameter (CV) were evaluated for each subject. Analysis was undertaken after evaluating the errors and the test-retest reliability of the Physilog device compared with an electronic walkway system (GaitRite) over the SWD with different walking speeds. While both systems were highly reliable with respect to the SV and GCT parameters (ICC>0.82), agreement for the gait variability was poor. Interestingly, our data revealed that the measured gait parameters over SWD and LWD were significantly different. LWD trials had a mean increase of 5.2% (p<0.05) in SV, and a mean decrease of 3.7% (p<0.05) in GCT compared with SWD trials. Although variability in both the SV and GCT measured during LWD trials decreased by an average of 1% relative to the SWD case, the drop was not significant. Moreover, reliability for gait variability measures was poor, irrespective of the instrument and despite a moderate improvement for LWD trials. Taken together, our findings indicate that for valid and reliable comparisons, test and retest should be performed under identical distance conditions. Furthermore, our findings suggest that the older subjects may choose different walking strategies for SWD and LWD conditions.

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.

Effects of home exercises and group training on functional abilities in home-dwelling older persons with mobility and balance problems. A randomized study

Background and aims: Exercise in older people may reduce falls and improve functional abilities. Less is known about the optimal amount of training. The aim of this study was to determine the effectiveness of home training, and whether group training in addition to home training enhances the effect. Methods: This randomized trial included 77 persons aged 75 years and older (mean 81, SD 4.5), living at home. Home training (HT) comprised twice-daily functional balance and strength exercises and 3 group meetings. Combined training (CT) included group training twice weekly and the same home exercises. The trial lasted 12 weeks. Physical therapists ran both programs. Exercises and falls were recorded daily. We assessed function at baseline, 3 and 9 months, and falls at one year. Results: Mean participation for group meetings was 2.5 out of 3 (HT group) and, for group training sessions, 21 out of 24 (CT group). The mean numbers of daily home sessions were 1.29 and 1.35 in the HT and CT groups. Overall improvement, but no group differences, were found at 3 months for walking speed, Figure of Eight, Timed Up & Go, Maximum Step Length, Timed Pick-up and Sit-to-stand (p<0.02). Posturography (p=0.85) and isometric quadriceps strength (p=0.26) showed no improvement. Function at 9 months was equivalent to baseline level. There were no group differences in fall rate (p=0.78) or time to first fall (p=0.84). Conclusions: Daily home training supervised by physical therapists improved functional abilities. Supplementary individualized group training gave no additional effect. The effect on function was not present 6 months after the end of the intervention.

Home training with and without additional group training in physically frail old people living at home: effect on health-related quality of life and ambulation

Objective: To test the effect of two exercise regimes on health-related quality of life (HRQoL) and ambulatory capacity. Design: Randomized controlled trial. Subjects: Seventy-seven community-dwelling physically frail people over 75 years of age (mean=81, SD=4.5). Interventions: Home training (HT, N =38) comprised twice daily functional balance and strength exercises and three group meetings. Combined training (CT, N =39) included group training twice weekly and the same home exercises. Interventions lasted 12 weeks. Physiotherapists ran both programmes. Home exercises were recorded daily. Main measures: HRQoL was assessed by SF-36, and ambulatory capacity by walking speed and frequency and duration of outdoor walks. Results: Following intervention, CT improved the SF-36 mental health index significantly more than HT (p =0.01). The SF-36 physical health index (p =0.002) and walking speed (p =0.02) demonstrated improvements, but no group differences. Six months after cessation of intervention there was still overall improvements on the mental health index (p =0.032), borderline overall improvements on the physical health index (p =0.057), higher weekly number of outdoor walks for the CT group than for the HT group (p =0.027) and an improved habitual walking speed in the CT group only (p =0.022). Conclusions: HT improved HRQoL and walking speed, but additional group training gave larger benefits on mental health. Group training away from home may be beneficial for mental health and ambulatory capacity.

Gait variability measures may represent different constructs

Many measures of gait variability have been reported, but the degree to which such measures are associated and thus represent a common construct is inconclusive. The purpose of this paper is to establish construct validity of commonly used spatio-temporal footfall variability and trunk variability measures taking into account the effect of measurement error. Twenty-three older individuals, aged 80+/-5 years performed four repeated walks at preferred speed, 0.97+/-0.16m/s. Gait data were obtained by an electronic walkway and by trunk accelerometry. Of initially 13 variability measures, five satisfied a reliability criterion of ICC> or =0.80 and were included in a subsequent construct validity analysis. Of these, step length variability and step time variability did not correlate significantly, while step length variability correlated closely with anteroposterior interstep trunk variability, and step time variability with vertical interstep trunk variability. Mediolateral interstep trunk variability did not correlate significantly with any of the other measures. This finding supports the notion that this measure may represent still a different aspect of variability. Different gait variability measures representing different constructs should be included in gait analysis to enhance our understanding of variability in gait.