Exercise testing to quantify effects of fatigue on functional capacity in patients with CFS.
Keller BA, Micale FG.:
The purpose of this study was to assess
the effects of post-exertional malaise (PEM) on
functional capacity and anaerobic threshold
in subjects diagnosed with chronic fatigue syndrome (CFS).
10 females and 2 males (41.3+1.11 yrs) diagnosed with CFS
by a physician experienced in the diagnosis of CFS.
To induce PEM, each subject completed a maximum exercise test on a cycle ergometer.
A second maximum exercise test was performed 24 hrs later
to assess the effects of exercise-induced PEM on functional capacity.
Maximum oxygen consumption (VO2max), maximum heart rate (HRmax),
anaerobic threshold (AT), maximum workload (Wmax),
workload at AT (ATwork), and respiratory exchange ratio (RER)
RER is an objective indicator of
substrate utilization and subject effort during exercise.
from test 1 to test 2 were
13.5% for VO2max (21.5 to 18.6 ml.kg-1.min-1; p<0.01),
8 bpm for HRmax (p<0.01),
18.8% for AT (12.0 to 9.7 ml.kg-1.min-1; p<0.05),
9.4% for Wmax (121 to 109 W, p<0.05), and
17.3% for ATwork (58.3 to 48.2 W; p<0.05).
However, there was no change in maximum RER
indicating that subject effort was maximum and also comparable during both tests.
Results indicate that
PEM decreased maximum functional capacity by more than 13% to below 5 METS;
a level at or below that which is required by many job-related activities and IADLs.
VO2max in healthy individuals is highly reproducible
over days and even months (r>.95), with a SEM of < 6%.
Thus, for subjects in this study,
an expected variation between tests would be ±1.29 ml.kg-1.min-1
in contrast to the observed decrease of 2.9 ml.kg-1.min-1.
PEM decreased AT to below 3 METS
(e.g., light-moderate speed walking),
which is a level of many activities considered to be sedentary in nature.
completion of sedentary ADLs and IADLs for those with CFS
requires production of energy via anaerobic processes
that will further contribute to PEM and exacerbate symptoms of CFS.
Since many daily activities fall into the 3-5 MET range,
individuals with CFS will exacerbate symptoms associated with PEM
simply by completing normal daily activities.
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