Discriminative Validity of Metabolic and Workload Measurements to
Identify Individuals With Chronic Fatigue Syndrome
Christopher R. Snell, Staci R. Stevens, Todd E. Davenport
(email@example.com) and J. Mark Van Ness
C.R. Snell, Department of Sport Sciences, University of the Pacific,
S.R. Stevens, Workwell Foundation, Ripon, California.
T.E. Davenport, Department of Physical Therapy, University of the
Pacific, 3601 Pacific Ave, Stockton, CA 95211 (USA).
J.M. Van Ness, Department of Sport Sciences, University of the Pacific.
Objectives Reduced functional capacity and post-exertional fatigue
following physical activity are hallmark symptoms of chronic fatigue
syndrome (CFS) and may even qualify for biomarker status. That these
symptoms are often delayed may explain the equivocal results for
clinical cardiopulmonary exercise testing among individuals with CFS.
Test reproducibility in healthy subjects is well documented. This may
not be the case with CFS due to delayed recovery symptoms. The
objectives for this study was to determine the discriminative validity
of objective measurements obtained during CPET to distinguish
individuals with CFS from non-disabled sedentary individuals.
Methods Gas exchange data, workloads and related physiological
parameters were compared between 51 individuals with CFS and 10
control subjects, all females, for two maximal exercise tests
separated by 24 hours.
Results Multivariate analysis showed no significant differences
between controls and CFS for Test 1. However, for Test 2 the
individuals with CFS achieved significantly lower values for oxygen
consumption and workload at peak exercise and at the
ventilatory/anaerobic threshold. Follow-up classification analysis
differentiated between groups with an overall accuracy of 95.1%.
Conclusions The lack of any significant differences between groups for
the first exercise test would appear to support a deconditioning
hypothesis for CFS symptoms. However, results from the second test
indicate the presence of a CFS related post-exertional fatigue. It
might be concluded that a single exercise test is insufficient to
reliably demonstrate functional impairment in individuals with CFS. A
second test may be necessary to document the atypical recovery
response and protracted fatigue possibly unique to CFS, which can
severely limit productivity in the home and workplace.
Received October 27, 2011.
Accepted June 23, 2013.
© 2013 American Physical Therapy Association