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

Background: 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).

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

Methods: 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.

Results: 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.

Conclusion: 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.