Keynote and Invited Abstracts |
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Chronic fatigue syndrome and the female athlete G
Scroop*, J Buckley, R Burnert, P Nemeth and C Sargent Chronic Fatigue Syndrome (CFS) is characterised by long-term disabling fatigue in a previously healthy and active individual where the diagnosis, in the absence of definitive laboratory tests, relies on an agreed grouping of clinical criteria. Although in several studies females predominate, it can affect both genders, across a broad age and activity spectrum and its aetiology is unknown. The fatigue is often present at rest and even the simplest physical tasks are achieved with difficulty leading to profound exhaustion and a prolonged period of recovery. There has been an assumption that CFS patients are ‘deconditioned’ with a reduction in aerobic fitness resulting from both a central and peripheral down-regulation in oxidative energy delivery processes and a ‘leftward’ shift in the lactate threshold. In contrast, our studies have found that cardio-respiratory function, maximal heart rate, maximal aerobic capacity and the lactate threshold in CFS patients are not different from an age and gender-matched healthy sedentary population. However, when working above the lactate threshold both male and female CFS patients exhibit an acceleration in lactic acid production such that any given work load and oxygen consumption blood lactate will be higher and result in earlier fatigue. Therefore, in endurance athletes, whose lactate threshold is typically shifted to the right, the onset of CFS, while not affecting maximal aerobic capacity or the lactate threshold could well result in a higher blood lactate than previously recorded during high intensity exercise. The mechanism of the accelerated glycolysis in CFS patients is unknown and although reversible with hyperoxic breathing the effect appears to be non-specific. When performing exercise of small muscle groups, such as the forearm, at work loads regarded as mainly accessing aerobic energy sources (<15%MVC), an abnormal lactate response was found in ~60% of male CFS patients but only ~20% of females, despite all patients meeting the same diagnostic criteria. The reasons for this gender difference at low work loads are uncertain. While forearm MVC was significantly higher in males than females with CFS the mean values in each case were not significantly different from healthy controls. It is concluded that while accelerated glycolysis may contribute to fatigue when both male and female CFS patients exercise at work loads above the lactate threshold, at lower work loads other central and/or peripheral factors are likely to be responsible for the gender bias in this disease. |
