SAT0727-HPR Criterion validity and reliability of a submaximal treadmill test in juvenile idiopathic arthritis patients
Authors: K. Risum, E. Edvardsen, A.M. Selvaag, Ø. Molberg, H. Dagfinrud, H. Sanner
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> For both research purposes and daily clinical practice, a feasible exercise test with acceptable measurement properties is needed to measure exercise capacity in juvenile idiopathic arthritis (JIA) patients. <h3>Objectives</h3> To evaluate the criterion-validity, test-retest reliability and inter-rater reliability of an eight-minute submaximal treadmill test, which can be used to estimate VO<sub>2peak</sub><sup>1</sup>, in JIA patients. <h3>Methods</h3> 59 patients with oligo- (n=30) and polyarticular (n=29) JIA (mean age (SD) 13.6 (2.2), 50 girls) participated in this study. They performed a maximal treadmill test until exhaustion to measure the VO<sub>2peak</sub> directly and the eight-minute submaximal treadmill test to estimate the VO<sub>2peak</sub>. A standardised formula was used to estimate the VO<sub>2peak</sub><sup>1</sup>. To evaluate the reliability, 37 patients also performed the submaximal treadmill test twice on the same day 1–4 weeks after the initial test. Paired t-tests were used to test potential differences between the tests. Criterion validity and reliability were evaluated with two ways mixed interclass correlation coefficient<sub>agreement</sub> (ICC). Limits of agreement (LoA) (Bland and Altman method), standard error of measurement (SEM<sub>agreement</sub>) and smallest detectable change (SDC<sub>95</sub>) were calculated to evaluate the measurement error of the submaximal treadmill test. <h3>Results</h3> No significant difference was found between the observed and estimated VO<sub>2peak</sub> (mL·kg<sup>-1</sup>·min<sup>-1</sup>), 44.8 (8.8) vs 43.2 (10.3) respectively, p=0.18. The single ICC (95% CI) value at individual level between the estimated and measured VO2peak was moderate; ICC 0.55 (0.34–0.70) while the ICC at group level was good; 0.71 (0.51–0.82). The measurement errors were large (SEM 6.5 and SDC<sub>95</sub> 18.0). The single ICC value for test-retest reliability and interrater reliability were good to excellent, 0.84 (0.71–0.91) and 0.92 (0.83–0.96), respectively. The ICC value at group level for test-retest reliability and interrater reliability were excellent, 0.91 (0.83–0.96) and 0.96 (0.91–0.98), respectively. There were no significant differences between estimated VO<sub>2peak</sub> (mL·kg<sup>-1</sup>·min<sup>-1</sup>) when comparing the results from the three performed submaximal treadmill tests. The measurement errors were moderate/large for both test-retest reliability and interrater reliability (table 1). The Bland Altman plots showed no systematic differences, but confirmed the large variability for both the validity and reliability (figure 1). <h3>Conclusions</h3> The submaximal treadmill test is valid for use in JIA patients on group level, but showed only moderate validity on an individual level. The test- retest and intra-rater reliability is good to excellent; however, the measurement errors are large. Our findings indicate that the submaximal treadmill test is not optimal for use in daily clinical practice to estimate VO<sub>2peak</sub> in individual patients and it is important to be aware of the large measurement errors. <h3>Reference</h3> [1] Ebbeling, et al. 1991. <h3>Disclosure of Interest</h3> None declared