Quality of the tools used to assess aerobic capacity in people with multiple sclerosis

Complexity and pitfalls in maximal exercise testing for persons with multiple sclerosis

BACKGROUND AND PURPOSE

Valid measurements of cardiorespiratory fitness in persons with multiple sclerosis (pwMS) are essential during inpatient rehabilitation for a precise evaluation of the current health status, for defining appropriate exercise intensities, and for evaluation of exercise intervention studies. We aim (i) to examine the proportion of pwMS who attain the American College of Sports Medicine (ACSM) criteria for maximal effort during graded cardiopulmonary exercise testing (CPET) and (ii) to provide insight into participant characteristics that limit maximal exercise performance.

METHODS

This cross-sectional study comprises a retrospective examination of ACSM criteria for maximal effort during graded CPET of n = 380 inpatient pwMS (mean age = 48 ± 11 years, 66% female). Chi-squared or Fisher's exact tests were conducted to compare differences in the distribution of criteria achieved. Participants' characteristics were examined as potential predictors using binary logistic regression.

RESULTS

Only 60% of the overall sample attained a respiratory exchange ratio ≥ 1.10. With regard to the definition applied, only 24% or 40% of the participants achieved an oxygen consumption plateau, and 17% or 50% attained the heart rate criterion. Forty-six percent met at least two of three criteria. Disability status, gender, disease course, and body mass index were associated with the attainment of maximal effort.

CONCLUSIONS

Our findings suggest that a relevant proportion of inpatient pwMS do not attain common criteria utilized to verify maximal oxygen consumption. Identified predictors for criteria attainment can be used to create models to predict cardiorespiratory fitness and to optimize CPET protocols in restrictive groups of pwMS.

Simplified indices of exercise tolerance in patients with multiple sclerosis and healthy subjects: A case-control study

Among patients with multiple sclerosis (MS), the impairment of exercise tolerance is closely related to disability. Maximal oxygen uptake (VO_2max ) is the gold standard to assess exercise tolerance in healthy subjects (HS). Among patients with MS, the accuracy of VO_2max measurement is often impaired because the patients are unable to reach the maximal exercise intensity due to interdependent factors linked to the disease (such as pathological fatigue, pain, lack of exercise habit, and lack of mobility). This study assesses the accuracy of simplified indices for assessing exercise tolerance, which are more suitable in patients with MS. They are simple in the way they are either measurable during submaximal exercise (oxygen uptake efficiency slopes (OUES), physical working capacity at 75% of maximal heart rate (PWC_75% ), oxygen consumption at a respiratory exchange ratio of 1 (VO₂ @RER1)) or not based on gas exchange analysis (peak work rate (PWR)-based predictive equation and PWC_75% ). All indices were significantly lower in the MS group compared to the HS group (P < .001). OUES appeared highly correlated (r > .70, P < .001) with VO_2peak , in both groups, without difference between groups. PWR-based prediction of VO_2peak showed a standard error of the estimate of 315 mL min^-1 in HS and 176 mL min^-1 in MS. PWC_75% did not correlate to VO_2peak in neither group. These findings suggest an impairment of exercise tolerance functions in mildly disabled persons with MS, independently from other factors. Submaximal indices involving gas exchange analysis or peakWR-based estimation of VO_2peak are usable to accurately assess exercise tolerance.

The 2-minute walk test is not a valid method to determine aerobic capacity in persons with Multiple Sclerosis

BACKGROUND:

Walking tests, like the 2-minute fast walk test, are simple, inexpensive performance-based tests, and therefore seem attractive to estimate the aerobic fitness in people with chronic diseases.

OBJECTIVE:

To determine the criterion validity of the 2-minute fast walk test for estimating aerobic capacity in patients with Multiple Sclerosis (MS), by comparing it with the peak oxygen uptake (VO2peak in mL/kg/min) as measured by Cardiopulmonary Exercise Testing (CPET) on a cycle ergometer.

METHODS:

The 2 min fast walk test was performed on a marked indoor trajectory, using a static start protocol. Aerobic capacity (VO2peak, in mL/kg/min) was derived from CPET on a cycle ergometer. Criterion validity was tested by means of Pearson’s correlation coefficient and should be at least 0.70 for a good criterion validity of the 2 min walk test. Linear regression analysis was applied to more precisely estimate VO2peak.

RESULTS:

In total 141 people with severe MS-related fatigue (mean age 47.0 years (range 23–68 years), 73% women, median disease duration 7.8 years (range 0.3 – 28.7 years)) performed both tests. The distance walked in two minutes ranged from 52.0 to 290.0 m (mean 175.1 m, sd 44.9 m), while the VO2peak varied between 11.31 and 40.28 mL/kg/min (mean 22.52 mL/kg/min, sd 6.07 mL/kg/min). The correlation between the 2 min walk test and VO2peak was 0.441 (95% CI: 0.309–0.570). The absolute residual error in estimated VO2peak was 5.47 mL/kg/min.

CONCLUSIONS:

Due to the poor correlation found between the 2 min walk test and VO2peak, the 2-min walk test cannot be recommended as a valid alternative for estimating aerobic capacity in persons with MS.