concurrentvalidityofthestepwatch -and-ac&graph ... ·...
TRANSCRIPT
Objec&ve: Accurate measurement of habitual physical ac5vity in children with cerebral palsy (CP) is essen5al to quan5fy ac5vity levels in this popula5on. This study aimed to inves5gate the concurrent validity between two commonly used ac5vity monitors, the StepWatchTM and Ac5Graph®GTIM accelerometer in ambulant children with CP.
Study par&cipants and se4ng: 29 children with CP (15 male; mean age 7.3 ± 2.9 years, range 2-‐16 years), classified at Gross Motor Func5onal Classifica5on System (GMFCS) I=5, II=17, III=7, aUending assessment of gait at a ter5ary mo5on analysis laboratory. Motor type and distribu5on were spas5c hemiplegia (n=15) or diplegia (n=14). Ankle-‐foot orthoses (AFOs) were worn by 22 par5cipants (76%)(unilateral=9, bilateral=13). 28 children completed barefoot and 19 completed AFO walking tasks.
Methods: Par5cipants walked at self-‐selected speed for 20 laps of a 10m oval track, with and without AFOs, wearing a StepWatchTM (SW) on the ankle and Ac5Graph® (AG) over the 4‑5th lumbar spine while video recording. Both devices were ini5alised to record in 3-‐second epochs. Video recordings were 5me coded and synchronized with both devices for comparison using BEST Analysis So`ware.
Concurrent validity was determined by comparing step counts and classifica5on of ac5vity intensity, between both devices and BEST counted steps. Paired and Independent t-‐tests were calculated between walking condi5ons and devices. Correla5ons were calculated using Pearson or Spearman correla5ons depending on data distribu5on. Bland and Altman ‘limits of agreement’ were calculated (mean difference(d)±2 standard devia5ons). Percentage agreement compared the ability both devices to discriminate physical ac5vity intensity. Data are mean difference (95% confidence interval), p<0.05.
Concurrent validity of the StepWatch™ and Ac&Graph® in ambulant children with cerebral palsy
E. McGuire1, L.E. Mitchell1, R.N. Boyd1 1 Queensland Cerebral Palsy and Rehabilita5on Research Centre, The University of Queensland, Herston, Qld, AUSTRALIA.
Results: Both devices under-‐es5mated step counts (Table 1).
The SW was strongly correlated to BEST in barefoot and AFO walking. In contrast, the AG was only moderately correlated to BEST for barefoot and weakly correlated during AFO walking (Table 2).
Table 2. Difference in measured versus observed step counts and correla5ons between measures for StepWatchTM and Ac5Graph® compared with the criterion measure (BEST) under barefoot and AFO walking condi5ons
Bland Altman limits of agreement demonstrate poor agreement for the AG and beUer agreement for the SW (Figure 1). There was good agreement (76%) between measures when classifying ac5vity intensity, though the SW appeared to over-‐es5mate ac5vity intensity 15% of the 5me.
Figure 1. Comparison between measures of step counts using Bland-‐Altman plots
Conclusion: The StepWatch™ demonstrated strong concurrent validity. Both devices are useful measures of physical ac5vity performance, and can be used to inves5gate habitual physical ac5vity in school aged children with CP.
The StepWatchTM is more accurately able to measure the frequency and intensity of steps however the Ac5Graph® may be more useful when classifying ac5vity intensity.
Key: *p<0.05, **p<0.001, p=significance value, d= mean difference, SE= standard error of mean (SD/√𝑛 ), r= Pearson correla5on, ρ=Spearman correla5on, BEST = BEST Analysis So`ware, GMFCS = Gross Motor Func5onal Classifica5on System.
Table 1. Walking 5me and steps measured by the Ac5Graph®, StepWatchTM compared to BEST so`ware walking barefoot and with AFOs
Barefoot N=28 d (95%CI)
AFO N=19 d (95%CI)
Time ± SD (s) 116.8 ± 73.0 123.2 ± 76.7 BEST ± SD (steps) 163 ± 48 146 ± 56 Ac&Graph® ± SD (steps) 98 ± 40 65 (47 -‐ 83)** 87 ± 38 58 (30 -‐ 86)** StepWatchTM ± SD (steps) 137 ± 49 26 (16 -‐ 37)** 119 ± 56 26 (9 -‐ 43)*
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a) Barefoot ActiGraph vs BEST
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b) AFO ActiGraph vs BEST
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c) Barefoot StepWatch vs BEST
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Sample Comparison (versus BEST)
Barefoot AFO d(Limits of agreement) Correla5on(r) d(Limits of agreement) Correla5on(ρ)
Whole Sample Ac5Graph 65 (-‐30.2 -‐ 155.9) 0.47* 58 (-‐71.2 -‐ 147.4) 0.39 StepWatch 26 (-‐42.9 – 103.2) 0.85** 26 (-‐44.8 – 81.7) 0.80**
<8 years Ac5Graph 83 (-‐15.9 – 138.4) 0.60* 54 (-‐77.7 – 194.4) 0.264 StepWatch 43 (-‐41.5 – 130.1) 0.84** 28 (-‐46.2 – 102.8) 0.845**
> 8 years Ac5Graph 38 (-‐27.1 – 102.6) 0.90** 21 (-‐39.6 – 81.3) 0.46 StepWatch 17 (-‐32.5 – 66.8) 0.91** 7 (-‐32.8 – 47.4) 0.29
GMFCS I & II Ac5Graph 55 (-‐36.4 – 146.6) 0.42 55 (-‐64.8 – 175.5) 0.77** StepWatch 19 (-‐25.5 – 63.6) 0.90** 20 (-‐22.4 – 63.6) 0.98**
GMFCS III Ac5Graph 96(26.1 – 166.8) 0.76* 66 (-‐53.4 – 185.0) 0.42 StepWatch 52 (-‐5.3 – 109.9) 0.90** 55 (-‐48.1 – 158.9) 0.44