Background: In a previous randomized controlled trial, we found that sitting isometric yoga improves fatigue in patients with chronic fatigue syndrome (CFS) who are resistant to conventional therapy. The aim of this study was to investigate possible mechanisms behind this finding, focusing on the short-term fatigue-relieving effect, by comparing autonomic nervous function and blood biomarkers before and after a session of isometric yoga. Methods: Fifteen patients with CFS who remained symptomatic despite at least 6 months of conventional therapy practiced sitting isometric yoga (biweekly 20 min practice with a yoga instructor and daily home practice) for eight weeks. Acute effects of sitting isometric yoga on fatigue, autonomic function, and blood biomarkers were investigated after the final session with an instructor. The effect of a single session of sitting isometric yoga on fatigue was assessed by the Profile of Mood Status (POMS) questionnaire immediately before and after the session. Autonomic nervous function (heart rate (HR) variability) and blood biomarkers (cortisol, DHEA-S, TNF-α, IL-6, IFN-γ, IFN-α, prolactin, carnitine, TGF-β1, BDNF, MHPG, and HVA) were compared before and after the session. Results: Sitting isometric yoga significantly reduced the POMS fatigue score (p < 0.01) and increased the vigor score (p < 0.01). It also reduced HR (p < 0.05) and increased the high frequency power (p < 0.05) of HR variability. Sitting isometric yoga increased serum levels of DHEA-S (p < 0.05), reduced levels of cortisol (p < 0.05) and TNF-α (p < 0.05), and had a tendency to reduce serum levels of prolactin (p < 0.1). Decreases in fatigue scores correlated with changes in plasma levels of TGF-β1 and BDNF. In contrast, increased vigor positively correlated with HVA. Conclusions: A single session of sitting isometric yoga reduced fatigue and increased vigor in patients with CFS. Yoga also increased vagal nerve function and changed blood biomarkers in a pattern that suggested anti-stress and anti-inflammatory effects. These changes appear to be related to the short-term fatigue-relieving effect of sitting isometric yoga in patients with CFS. Furthermore, dopaminergic nervous system activation might account for sitting isometric yoga-induced increases in energy in this patient population.
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