Science and Legal News on Postexertional Malaise

By K. Kimberly McCleary, President & CEO

From 2006 to 2007, the Solve ME/CFS Initiative , through your donations, funded a study by investigators at the University of the Pacific that investigated the physiologic basis of postexertional malaise in CFS. Two papers describing interesting results from this study were published back-to-back in the December issue of the Journal of Chronic Fatigue Syndrome.

Both papers address testing the functional capacity of CFS patients at more than one time point interval—what the investigators call a “test-retest” approach. One paper, “Diminished Cardiopulmonary Capacity During Postexertional Malaise,” identifies a reproducible physical marker when CFS patients are subjected to an exercise test-retest protocol. The other paper, “Legal and Scientific Considerations of the Exercise Stress Test,” explores the use of a test-retest protocol for assessing CFS-related disability.

Physical exercise often exacerbates the symptoms that characterize CFS, resulting in a postexertional relapse that can last for 24 hours or more. In fact, postexertional malaise is a hallmark of CFS, and many investigators have used exercise testing to identify markers of fatigue. Most (basic, non-CFS) exercise physiology studies focus on the ability of the body to transport and use oxygen. To survive and to carry out activity, the body must extract oxygen from the atmosphere and transport it to every cell in the body, where it’s used for essential metabolic processes. Oxygen and energy are inexorably linked.

When an exercise stress test is done in a lab, the subject performs a physical activity (like riding a stationary bicycle) while wearing a mask that determines how much oxygen is consumed—otherwise known as VO2, for volume of oxygen consumed. Blood pressure and heart rate are also monitored the entire time. An important aspect of the exercise test is to ensure that the subject is exerting maximal physical effort and not feigning fatigue. This is done by calculating a respiratory quotient that measures the chemical and physical changes that occur during metabolism.

Reduced capacity is evident using the test-retest approach

In the cardiopulmonary capacity paper by J. Mark VanNess, PhD, Christopher Snell, PhD, and Staci Stevens, the research team studied six CFS patients and six healthy but sedentary control subjects by putting them through an exercise test on two consecutive days. The first exercise test showed no differences between CFS patients and healthy controls. However, after the second exercise test 24 hours later, CFS patients displayed significantly decreased oxygen consumption—both when compared to the mean, or middle, VO2 of their first test and when compared to the VO2 of the healthy controls during the second test. The authors concluded that “the fall in oxygen consumption among the CFS patients on the second test suggests metabolic dysfunction rather than sedentary lifestyle as the cause of diminished exercise capacity in CFS.”

The researchers noted that the CFS patients demonstrated maximal effort on both exercise tests. They also suggest that decreased oxygen consumption on day 2 is a distinctive feature of CFS since cardiopulmonary exercise test-retest protocols in other conditions, such as pulmonary hypertension, cystic fibrosis and obstructive pulmonary disease, do not show a similar VO2 decrease. This strongly supports the suspected oxidative and metabolic dysfunction that has been hypothesized as associated with CFS pathology.

Implications for CFS disability claims

The paper by Margaret Ciccolella, EdD, JD, and Stevens, Snell and VanNess examined the legal and scientific considerations of the exercise stress test for CFS disability claims—demonstrating the shortfalls of using a single test to determine disability in people with CFS.

The exercise stress test is one of several tools used by the Social Security Administration (SSA) to determine disability. For CFS disability, as with all other conditions, the SSA requires two things: proof of the existence of a medically determinable impairment and the inability to do any kind of work. The SSA considers an abnormal exercise test an objective medical impairment for CFS.

In order to receive disability benefits for CFS, the evidence for both the medically determined impairment and inability to work must be objective. An exercise test is objective, but as the test-retest study (described above) demonstrates, a single exercise test does not show a difference in oxygen consumption between people with CFS and healthy controls. Used alone, a single exercise test may not return compelling evidence for a CFS disability claim. However, a second test conducted 24 hours after the first exercise challenge likely would provide the objective documentation of postexertional malaise. According to the authors, the initial data from this study suggests that “the test-retest format offers a superior basis to establish disability consistent with SSA policy and other relevant case law.”

This research, funded through the Solve ME/CFS Initiative’s research program, is just one example of how your financial support is helping to increase our knowledge of CFS and lead to practical benefits for CFS patients.


VanNess M, Snell C, Stevens S. Diminished cardiopulmonary capacity during post-exertional malaise. Journal of Chronic Fatigue Syndrome 2007; 14(2): 77-85

Ciccolella M, Stevens S, Snell C, VanNess M. Legal and scientific considerations of the exercise stress test. Journal of Chronic Fatigue Syndrome 2007; 14(2): 61-75

K. Kimberly McCleary served as the Association’s chief staff executive from 1991-2013.

February 1, 2008