ANAEROBIC THRESHOLD FOR THE DETERMINATION OF FUNCTIONAL CAPACITY IN CHRONIC FATIGUE SYNDROME (CFS).

Abstract

Physiological responses to exercise potentially provide important insights to the underlying pathogenic mechanisms of CFS. However, exercise studies with CFS patients are often plagued by problems of small sample sizes, possibly a result of some patients being unwilling or unable to fulfill traditional criteria for maximal effort. A solution to this problem could be to employ measures of oxygen consumption at anaerobic threshold (AT) in lieu of maximal VO2 as an indicator of functional capacity. PURPOSE To compare CFS patients at differing levels of impairment (American Medical Association classifications) for VO2 at AT and AT as a percentage of peak VO2. METHODS Peak VO2 obtained during exercise testing to volitional fatigue was used to assign 137 CFS patients into one of four impairment classifications. MANOVA with univariate follow-up was used to examine differences between groups for VO2 at AT and AT as percentage of peak VO2. RESULTS AT could not be determined for any patient in Class 4 (severely impaired). There were significant differences between all three remaining groups for VO2 at AT (p<0.001) with the more severely impaired patients showing lower values. No differences were observed for AT as a percentage of peak VO2 (p = 0.08). CONCLUSIONS Significant group differences for VO2 at AT suggests this measure may serve as a useful indicator of functional status in the absence of reliable peak oxygen consumption values. Absence of differences between groups for AT as a percentage of peak VO2 supports this assertion and suggests that patients were correctly classified. However, the value of VO2 at AT as an alternative indicator of functional status was limited in this study by an inability to determine AT for some patients, particularly those classified as severely impaired.