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. 2016 Oct 7:8:31.
doi: 10.1186/s13102-016-0056-7. eCollection 2016.

Criterion validity and reliability of a smartphone delivered sub-maximal fitness test for people with type 2 diabetes

Cecilie Fau Brinkløv  1 , Ida Kær Thorsen  1 , Kristian Karstoft  1 , Charlotte Brøns  2 , Laura Valentiner  3 , Henning Langberg  3 , Allan Arthur Vaag  2 , Jens Steen Nielsen  4 , Bente Klarlund Pedersen  1 , Mathias Ried-Larsen  1   5
Affiliations

Criterion validity and reliability of a smartphone delivered sub-maximal fitness test for people with type 2 diabetes

Cecilie Fau Brinkløv et al. BMC Sports Sci Med Rehabil. .

Abstract

Background: Prevention of multi-morbidities following non-communicable diseases requires a systematic registration of adverse modifiable risk factors, including low physical fitness. The aim of the study was to establish criterion validity and reliability of a smartphone app (InterWalk) delivered fitness test in patients with type 2 diabetes.

Methods: Patients with type 2 diabetes (N = 27, mean (SD) age 64.2 (5.9) years, BMI 30.0 (5.1) kg/m2, (30 % male)) completed a 7-min progressive walking protocol twice (with and without encouragement). VO2 during the test was assessed using indirect calorimetry and the acceleration (vector magnitude) from the smartphone was obtained. The vector magnitude was used to predict VO2peak along with the co-variates weight, height and sex. The validity of the algorithm was tested when the smartphone was placed in the right pocket of the pants or jacket. The algorithm was validated using leave-one-out cross validation. Test-retest reliability was tested in a subset of participants (N = 10).

Results: The overall VO2peak prediction of the algorithm (R2) was 0.60 and 0.45 when the smartphone was placed in the pockets of the pants and jacket, respectively (p < 0.001). The mean bias (limits of agreement) in the cross validation was-0.4 (38) % (pants) and-0.1 (46) % (jacket). When the smartphone was placed in the jacket a significant intensity dependent bias (r = 0.5, p = 0.02) was observed. The test-retest intraclass correlations were 0.85 and 0.86 (p < 0.001), for the pants and jacket, respectively. No effects of encouragement were observed on test performance.

Conclusion: In conclusion, the InterWalk Fitness Test is accurate and reliable for persons with type 2 diabetes when the smartphone is placed in the side pocket of the pants for. The test could give a fair estimate of the CRF in absence of a progressive maximal test during standardized conditions with the appropriate equipment.

Trial registration: www.clinicaltrials.org (NCT02089477), first registered (prospectively) on March 14th 2014.

Keywords: Exercise; Fitness; Reliability; Smartphone; Type 2 diabetes mellitus; Validity.

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Figures

Fig. 1
Fig. 1
Photo of placements and setup. 1a: Smartphone placed in the side pocket of the pants (lower position, LP), 1b: Smartphone placed in the side pocket of the jacket (upper position, UP)
Fig. 2
Fig. 2
The partial correlations between VO2peak and vector magnitude during the last 30 s of the test when the smartphone was placed in the lower position, smartphone placement in the right side pocket of the pants (Panel a) and in upper position, smartphone placement in the right side pocket of the jacket (Panel b). The dotted line is the best fit line. Triangles (▲) represent observations during the test with encouragement and crosses (X) are observations during the test without encouragement. The grey shaded area is the 95 % confidence interval
Fig. 3
Fig. 3
The accuracy (mean bias) and precision (±1.96 Standard deviation (SD)) of the VO2peak prediction algorithms for the lower (panel a) and the upper (panel b) position of the smartphone placement in the ‘leave-on-out cross validation’. The dotted line is the best fit line and represents the bias of the predicted values. Triangles (▲) represent the predicted values from the VM derived from the smartphone when placed in the upper position and crosses (X) are predicted values from the lower position
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