Article Index

Exercise challenge

B.Keller (New York, USA) studied the effects of fatigue on functional capacity in patients with CFS. There is a need to quantify impairment. The cardiopulmonary exercise test (CPET) measures functional impairment and is an objective measure of energy expenditure and physical work. It is validated and reliable in health and disease, but she questioned whether it was useful in CFS. The purpose of the study was to measure the effects of post-exertional malaise in CFS. She concluded that patients’ disability went from mild to moderate on first test and from moderate to severe on second 24 hours later. Looking at maximum exercise tests, it was shown that those with CFS will exacerbate symptoms associated with post-exertional malaise simply by completing normal daily activities.

C.Snell (Stockton, USA) then covered the importance of exercise challenge, and the need for a standardised measured approach in diagnosis and management.  He described fatigue as a reduced efficiency as a result of doing “work”. Some measures can be indirect (e.g., heart rate) or direct (e.g., gas exchange). Field tests are easy to administer and require minimal equipment but are unmonitored and therefore less likely to be accurate. Motivation and pacing both play a big role in the results. He discussed the PACE trial and showed that the results actually equate to 1.94 – 2.35 mph and at 2 METS this equates to 7ml/min/Kg oxygen. The NY Heart Association would classify this as “severely disabled”. Anything greater than 3mph is the anaerobic threshold for most CFS patients. Direct assessment of aerobic capcity should be the gold standard. CPET is uniquely able to quantify efficiency with measures of workload and the metabolic cost of the work. Healthy people do better on a second test, but in CFS there is a massive drop. Post-exertional malaise (PEM) is an exacerbation of symptoms after exertion. Most healthy people will recover in 48 hours, but in the group studied, only one patient with CFS recovered in 48 hours. The respiratory exchange rate (RER) is the most reliable gauge of subject effort—it encompasses an analysis of expired gases.