Validity and reliability of VO₂-max measurements in persons with multiple sclerosis

Direct measurement of whole body maximal oxygen consumption (VO2-max test) is considered the gold standard when assessing cardiorespiratory fitness. Nonetheless, the validity and reliability of the test have not been examined in persons with multiple sclerosis (PwMS).

To investigate the validity and reliability of VO2-max measurements in PwMS, and additionally to compare these measures to those of healthy controls.

Twenty PwMS completed two incremental VO2-max tests on a leg cycling ergometer. Test validity was analyzed based on the first VO2-max test in the total sample and in patient subgroups based on Expanded Disability Status Scale (EDSS) scores (EDSS≤2.5, n=10 and EDSS≥3.0, n=10) by evaluation of the primary VO2 plateau criterion and four common secondary validity criteria. Data from 20 age- and gender-matched healthy controls were used for comparison. The second VO2-max test was used to establish day-to-day reliability.

In PwMS 40% were able to achieve the primary validity criterion for VO2-max measurements, while 65-95% were able to achieve the secondary criteria. This corresponded to the age-matched healthy controls. Strong correlations were found between measurements of VO2-max and between the validity criteria from test 1 compared to test 2 in PwMS. MS disability level did not influence criteria attainment. The variability analysis exhibited a 95% prediction interval of -238 to 201 mL·min(-1) (-9.8 to 8.1%) for the difference between the two measurements of VO2-max.

In mild to moderately impaired PwMS less than half achieve the primary validity criterion when performing a VO2-max test, but the high reliability and the better achievement of the secondary criteria implies that a valid test of VO2-max can be performed, at a level corresponding to that of healthy controls. The day-to-day variation implies that a change of more than 10% in VO2-max is required to be interpreted as a real change.