Chronic Fatigue and the HPA Axis: Conservation Mode
Chronic fatigue — the profound, unrestorative exhaustion that doesn’t improve with rest and that crashes after even mild exertion — is one of the most misunderstood conditions in medicine. Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) affects an estimated 17–24 million people globally. It has historically been dismissed as psychological, poorly understood, and poorly treated.
Evolutionary medicine and neuroendocrinology together offer a coherent framework for what is actually happening.
The HPA Axis: The Body’s Stress Regulator
The hypothalamic-pituitary-adrenal (HPA) axis is the central stress response system. When a threat is detected, the hypothalamus releases CRH → the pituitary releases ACTH → the adrenal glands release cortisol.
Cortisol has two primary immediate functions: it mobilises glucose for energy, and it suppresses inflammation to keep the immune response from becoming self-damaging during acute threat. In the short term, this is the system working perfectly. The problem arises when the threat is chronic and unresolvable.
Two Stages of HPA Dysregulation
Stage 1: Hypercortisol. Early chronic stress produces elevated cortisol — the system is in overdrive. This phase is characterised by anxiety, insomnia, irritability, weight gain, and immune suppression. Many people recognise “burnout” as this stage.
Stage 2: Hypocortisol. After sustained hyperactivation, the HPA axis eventually downregulates. Cortisol receptors become desensitised; the system loses responsiveness. The result is paradoxically low cortisol despite ongoing stress — and the body enters a fundamentally different state. Low cortisol cannot mobilise adequate energy. Inflammation, normally suppressed by cortisol, becomes unchecked. The body downshifts into a low-energy, high-inflammation, high-pain-sensitivity state. This is ME/CFS.
The Evolutionary Logic of Conservation Mode
Why would the HPA axis downshift into this state? Because energetically, it makes sense. If a prolonged threat cannot be resolved, the organism cannot sustain emergency mobilisation indefinitely. Downshifting to a low-energy conservation mode — reducing activity, withdrawing from further stress exposure — is the biological equivalent of an emergency shutdown to preserve core function.
This is not weakness or laziness. It is a physiological state — as real and as measurable as any other disease state.
OQ’s Approach
The vagus nerve is both downstream of the HPA axis and a regulator of it. High vagal tone promotes HPA resiliency — it is the primary physiological “off switch” for the stress response. Dr. Sakata’s work with chronic fatigue patients focuses on supporting vagal tone through osteopathic treatment, addressing the postural and thoracic mechanics that restrict diaphragmatic breathing (a key vagal activator), and supporting the sleep quality that is essential for HPA reset.
This is not a rapid fix. HPA dysregulation that has developed over years resets over months. But the trajectory changes meaningfully.
FAQ
Is ME/CFS a real disease?
Yes. Research has identified consistent biomarkers: HPA axis dysregulation, immune activation patterns, mitochondrial dysfunction in immune cells, and reduced natural killer cell function. It is a measurable physiological state, not a psychological construct.
Why does exertion make ME/CFS worse?
Post-exertional malaise (PEM) reflects the inability of the HPA-fatigued system to recover from energy demands. Physical activity normally activates cortisol to support recovery; in ME/CFS, this response is blunted, and exertion produces a prolonged worsening.
Can osteopathy help ME/CFS?
Gentle osteopathic treatment supporting vagal tone, reducing allostatic load, and improving sleep quality can be beneficial — if paced appropriately to avoid triggering PEM. The key is working with the system’s current capacity, not against it.
Living with chronic fatigue that no one has been able to explain? An evolutionary medicine perspective may offer a new framework for understanding and managing it. Book →