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Mark VanNess, PhD, & Chris Snell, PhD
Working to understand why activity causes relapse inCFIDS
Mark VanNess, PhD, and Chris Snell, PhD, are among the few
exercise physiologists studying
and their colleague Staci Stevens (a member of the federal CFS Advisory
Committee and a person with
CFIDS), use their
knowledge of energy production and utilization to better understand why
CFIDS patients feel so much worse after
activity. Dr. VanNess is an assistant professor and Dr. Snell a professor in the
Department of Sport Sciences at the University of the Pacific.
Q: What is exercise physiology?
VanNess: I break exercise physiology
into two parts, the first being the acute responses to exercise, looking at
changes in muscle contraction, energy delivery, heart rate, blood flow and
processes like these when you exercise. The second part is teaching athletes or
people with health conditions to operate at a higher level of efficiency and
higher work output as a result of training. We’re studying the acute response to
exer- tion in our CFIDS research.
Q: What exercise testing do you do with your
Snell: We use either a treadmill or
a cycle ergometer that is manufactured to work at different outputs.
VanNess: We do a cardiopulmonary
analysis where we collect the expired air for analysis of oxygen utilization and
carbon dioxide production, and we also measure blood pressure and heart rate
response to exercise. With those variables you can look at the patients’ resting
levels and then, as they start doing exercise, look at the acute responses — the
responses that provide energy during exercise.
With the maximal exercise test, you take subjects all the way
up to their peak exertion, so you’re able to measure their peak oxygen
utilization and carbon dioxide production, and how well they’re able to activate
their heart to bring heart rate up and increase systolic blood pressure.
Snell: As you increase your effort
you’re no longer able to supply sufficient oxygen to active muscles to
completely metabolize the energy. So you go into a secondary energy system,
called the anaerobic energy system, which is quite deviously designed to allow
you to continue to work even though you’re not using oxygen to produce the
energy. In anaerobic metabolism the byproducts of exertion are not completely
metabolized, so you end up with lactic acid building up in the bloodstream,
eventually compromising your ability to continue working. You enter a condition
called “oxygen debt.” It’s like being overdrawn at the bank — you have to pay it
back before you can start spending again.
VanNess: Our research is unique in
that we have looked at determination of anaerobic threshold in
CFIDS . In order to determine anaerobic
threshold you have to do an incremental exercise test to peak effort.
Q: Your research has also shown that
CFIDS patients have a lower anaerobic threshold
than healthy sedentary controls. What does that mean?
VanNess: If athletes spend too much
time above their anaerobic threshold, they become exhausted and have to rest. We
think the same applies to
CFIDS patients. If
their aerobic metabolism is lower than expected, then they’d spend more time
above that anaerobic threshold doing their regular activities. That may be
producing prolonged recovery time and more exhaustion after activities of daily
Snell: In real terms, anaerobic
threshold is the point at which you should stop working if you expect to recover
in a reasonable amount of time. We can establish that very accurately with an
exercise test and match that to a specific heart rate. A heart rate monitor can
be used by the patient as a biofeedback mechanism to determine the point where
they need to stop activity if they want to be able to function the next day. So
it’s becoming a useful, practical way people can monitor output during the day
to allow them to stay within their energy envelope.
Q: What else have you learned about
Snell: We have access to the
baseline data for 189 Phase III Ampligen treatment trial subjects. So we have a
large subject pool of what we think have been consistently diagnosed
CFIDS patients. We’ve found that those who have
abnormal RNase-L activity (an indication of immune activation) are lower
func-tioning than those who don’t.
VanNess: The maximal exercise test
is a very good measure of a patient’s functional capacity. If you look at the
results of an exercise test and you’re not familiar with
CFIDS, the patient’s function (but not the
oxygen and carbon dioxide exchange measures) looks like that of a patient with
cardiovascular or pulmonary disease. The exercise test can be used to rule out
these other causes of fatigue when making a
Q: Does your data compare with the findings of
orthostatic intolerance in CFIDS?
VanNess: We’ve looked at the
systolic blood pressure response to exercise. And, interestingly enough, it is
blunted quite profoundly in patients with
CFIDS . I think it’s two ways of looking at the
same thing: orthostatic intolerance is an inability to regulate blood pressure
within normal parameters. I think the same thing occurs during exercise when
you’d normally see a large rise in systolic blood pressure to provide blood flow
during exercise. Patients with
activate that system well, so they may have a failure to perfuse (send blood to)
muscle tissues during exercise.
research studies are you planning?
Snell: We have two other ideas that
we’re pursuing on a small scale. One of them is the idea of doing two exercise
tests separated by 24 hours. In a healthy individual when you do two exercise
tests a day apart, the results are about the same. In a
CFIDS patient, because of the post-exertional
malaise, peak oxygen consumption is dramatically less on the second exercise
test. We’d like to get funding to examine that a little more closely and not
just describe the phenomenon, but try to determine why it’s so much less the
The second idea is trying to use the exercise test as a
standardized stressor to look at post-exertional malaise. We’ll look at some of
the immune and hormonal responses and neurocognitive effects after exercise. So,
we want to truly describe what post-exertional malaise entails in a