Validity and reliability of VO₂-max testing in persons with Parkinson's disease

Direct whole body assessment of maximal oxygen consumption (VO₂-max test) is considered the gold standard when assessing cardiorespiratory fitness (VO₂-max) in healthy people. VO₂-max is also an important health and performance indicator for persons with Parkinson's disease (pwPD) and is often used when prescribing exercise and evaluating aerobic exercise interventions. However, no study has examined the content validity of the VO₂-max test in pwPD as well as the test-retest reliability (i.e., day-to-day variation) in both the ON and OFF medication state. Therefore, the present study investigated the content validity and test-retest reliability of the VO₂-max test in pwPD both ON and OFF medication.

Twenty pwPD completed four VO₂-max tests (two tests ON and two tests OFF medication), in a randomized order, separated by four to sixteen days. The first tests ON and OFF medication were used to assess content validity based on attainment of five pre-defined end-criteria (one primary and four secondary). Reliability was examined by intraclass correlation coefficients (ICC) and the day-to-day variation of the two ON and OFF medication tests.

In pwPD, 50% and 60% attained the primary end-criterion ON and OFF medication, respectively. A higher proportion (i.e., 70-90%) attained the secondary end-criteria both ON and OFF medication with no difference between medication states. Day-to-day variations were 1.2 and 1.8 ml O₂/kg/min, while ICC_2.1 were 0.97 (95%-CI: 0.92; 0.99) and 0.96 (95%-CI: 0.90; 0.98) ON and OFF medication, respectively.

The VO₂-max test has an acceptable content validity and excellent day-to-day reliability ON and OFF medication in pwPD.