Post-exertional malaise (PEM) is a hallmark symptom of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). We monitored the evolution of 1157 plasma metabolites in 60 ME/CFS (45 female, 15 male) and 45 matched healthy control participants (30 female, 15 male) before and after 2 maximal cardiopulmonary exercise test (CPET) challenges separated by 24 hours, with the intent of provoking PEM in patients. Four time points allowed exploration of the metabolic response to maximal energy-producing capacity and the recovery pattern of participants with ME/CFS compared with the healthy control group. Baseline comparison identified several significantly different metabolites, along with an enriched percentage of yet-to-be identified compounds. Additionally, temporal measures demonstrated an increased metabolic disparity between cohorts, including unknown metabolites. The effects of exertion in the ME/CFS cohort predominantly highlighted lipid-related as well as energy-related pathways and chemical structure clusters, which were disparately affected by the first and second exercise sessions. The 24-hour recovery period was distinct in the ME/CFS cohort, with over a quarter of the identified pathways statistically different from the controls. The pathways that are uniquely different 24 hours after an exercise challenge provide clues to metabolic disruptions that lead to PEM. Numerous altered pathways were observed to depend on glutamate metabolism, a crucial component of the homeostasis of many organs in the body, including the brain.

Background and Objectives: Post-exertional malaise (PEM) is the hallmark of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), but there has been little effort to quantitate the duration of PEM symptoms following a known exertional stressor. Using a Symptom Severity Scale (SSS) that includes nine common symptoms of ME/CFS, we sought to characterize the duration and severity of PEM symptoms following two cardiopulmonary exercise tests separated by 24 h (2-day CPET). Materials and Methods: Eighty persons with ME/CFS and 64 controls (CTL) underwent a 2-day CPET. ME/CFS subjects met the Canadian Clinical Criteria for diagnosis of ME/CFS; controls were healthy but not participating in regular physical activity. All subjects who met maximal effort criteria on both CPETs were included. SSS scores were obtained at baseline, immediately prior to both CPETs, the day after the second CPET, and every two days after the CPET-1 for 10 days. Results: There was a highly significant difference in judged recovery time (ME/CFS = 12.7 ± 1.2 d; CTL = 2.1 ± 0.2 d, mean ± s.e.m., Chi² = 90.1, p < 0.0001). The range of ME/CFS patient recovery was 1–64 days, while the range in CTL was 1–10 days; one subject with ME/CFS had not recovered after one year and was not included in the analysis. Less than 10% of subjects with ME/CFS took more than three weeks to recover. There was no difference in recovery time based on the level of pre-test symptoms prior to CPET-1 (F = 1.12, p = 0.33). Mean SSS scores at baseline were significantly higher than at pre-CPET-1 (5.70 ± 0.16 vs. 4.02 ± 0.18, p < 0.0001). Pharmacokinetic models showed an extremely prolonged decay of the PEM response (Chi² > 22, p < 0.0001) to the 2-day CPET. Conclusions: ME/CFS subjects took an average of about two weeks to recover from a 2-day CPET, whereas sedentary controls needed only two days. These data quantitate the prolonged recovery time in ME/CFS and improve the ability to obtain well-informed consent prior to doing exercise testing in persons with ME/CFS. Quantitative monitoring of PEM symptoms may provide a method to help manage PEM.

Peak oxygen uptake (VO2peak) of patients with end-stage renal failure treated with hemodialysis is very low. The improvement of anemia with recombinant human erythropoietin (rHuEPO) results in a very small change in VO2peak. This change is minimal compared with the magnitude of change in hematocrit, suggesting that other factors continue to limit exercise tolerance. This article reviews the physiology of oxygen transport and the determinants of VO2peak. Anemic hemodialysis patients are limited by a reduced cardiac output response to exercise and an inability to widen the arterio-venous oxygen difference. The lack of change in cardiac output and a remaining low arterio-venous oxygen difference following improvement of anemia with rHuEPO therapy suggest an underlying muscle limitation to exercise. Evidence for this muscle limitation is presented. Exercise training may improve the ability of muscle to use oxygen, thus optimizing the effect of the increased hematocrit resulting from rHuEPO therapy.

Objective: Assessment of physical activity and exercise prescription has been widely supported by many organizations, yet provision of such services remains limited in the United States. We sought to uncover why such services have not been widely adopted. Design: The American Medical Society for Sports Medicine organized a task force to canvas physicians and survey the American Medical Society for Sports Medicine membership. Setting: Peer-to-peer and telecommunication discussions and web-based questionnaires. Participants: Sports medicine physicians in the United States. Interventions: None. Main Outcome Measures: Percentage of sports medicine physicians who provide exercise management services and mechanisms of billing for exercise management, identify barriers to such services, and identify industry collaborations for promoting physical activity through physicians. Results: Three of 4 sports medicine physicians spend at least 1 min encouraging exercise with patients, using Evaluation and Management codes to bill or receive credit. Exercise counseling is often bundled within other patient care. Few health plans leverage the patient's relationship with a primary care physician to promote exercise. Most employed sports medicine physicians do not receive incentives to incorporate exercise counseling into practice, and only 1 in 6 have decision-making authority to hire an exercise professional. Major obstacles are the lack of a business model and knowledge about exercise prescription. Conclusion: The existing E&M codes adequately characterize the work, but physicians desire greater payment or credit for providing exercise management services. Physicians desire to do more exercise prescription, but health system bureaucracy, inadequate support, and economic disincentives are barriers to the provision of exercise management services.