Activity rhythm degrades after strenuous exercise in chronic fatigue syndrome

Post-exertional exacerbation of symptoms is one of the major characteristics of chronic fatigue syndrome (CFS). In this study, we evaluated the hypothesis that disturbances in circadian chronobiological regulation may play a role in generating this phenomenon. We recorded physical activity for 6-day periods in 16 women (10 CFS and 6 sedentary healthy controls, CON) before and after performing a maximal treadmill test. We calculated activity rhythms by computing autocorrelation coefficients by cutting 1 day apart from the data as a template and sliding it sequentially through each of the other days; all of 6 days were used as the templates. The peak value of autocorrelation coefficient (R) and the time between peak R's (circadian period, CP) were calculated. CFS patients had a lengthening (P < .05) of mean circadian period (MCP) that was longer than 24 h (P < .05), while MCP in CON remained unchanged. No difference was found in the standard error of each subject's MCP (circadian period variability, CPV) before and after exercise for both groups. We interpret this increase in circadian rest-activity period seen in CFS patients following exercise to indicate that exhaustive exercise interferes with normal entrainment to 24-h zeitgeber(s). This effect may be associated in part with the common patient complaint of symptom worsening following exertion.