Criterion validity and reliability of a smartphone delivered sub-maximal fitness test for people with type 2 diabetes.
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). VO2during the test was assessed using indirect calorimetry and the acceleration (vector magnitude) from the smartphone was obtained. The vector magnitude was used to predict VO2peakalong 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 VO2peakprediction 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.


CONCLUSIONS
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.


BACKGROUND
www.clinicaltrials.org (NCT02089477), first registered (prospectively) on March 14th 2014.
Centre for Physical Activity Research, Finsen Centre, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.
Cecilie Fau
CF
Brinkløv
Centre for Physical Activity Research, Finsen Centre, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.
Ida Kær
IK
Thorsen
Centre for Physical Activity Research, Finsen Centre, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.
Kristian
K
Karstoft
Department of Endocrinology (Diabetes and Metabolism), Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.
Charlotte
C
Brøns
Department of Public Health, Section of Social Medicine, University of Copenhagen, Henrik Pontoppidans Vej 4, 2200 Copenhagen, Denmark.
Laura
L
Valentiner
Department of Public Health, Section of Social Medicine, University of Copenhagen, Henrik Pontoppidans Vej 4, 2200 Copenhagen, Denmark.
Henning
H
Langberg
Department of Endocrinology (Diabetes and Metabolism), Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.
Allan Arthur
AA
Vaag
Department of Endocrinology, Odense University Hospital, Sdr. Boulevard 29, Entrance 112, 3rd floor, 5000 Odense, Denmark.
Jens Steen
JS
Nielsen
Centre for Physical Activity Research, Finsen Centre, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.
Bente Klarlund
BK
Pedersen
Centre for Physical Activity Research, Finsen Centre, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.|The Danish Diabetes Academy, Odense University Hospital, Sdr. Boulevard 29, Entrance 112, 3rd floor, 5000 Odense, Denmark.
Mathias
M
Ried-Larsen
Exercise; Fitness; Reliability; Smartphone; Type 2 diabetes mellitus; Validity