The nervous system of people with post-COVID fatigue was found to be underactive in key areas, increasing the risk of fatigue -- one of the most common symptoms of long COVID, according to researchers.

A team from Newcastle University in the UK carried out a battery of behavioural and neurophysiological tests on people suffering from post-COVID fatigue and compared them to people without fatigue.

The researchers discovered people with post-COVID fatigue showed under activity in three specific areas of the nervous system.

They found a slower reaction in specific areas of the brain because of under activity in specific cortical circuits; an imbalance in the autonomic nervous system -- the network of nerves that regulates unconscious body processes such as blood pressure and the rate of breathing was found to be impaired. This can have wide-ranging effects on several different body processes.

They also found muscle abnormalities -- muscle fibres became more easily fatigued after exercise than in people without post-COVID fatigue.

"These abnormalities in the results on objective tests show that fatigue in long COVID is a measurable disease and these tests may, in time, help us understand how changes in the nervous system contribute to fatigue," said Dr Demetris Soteropoulos, Senior Lecturer in Motor Systems Neuroscience at the University.

The research has been published in Brain Communications. A group of 37 volunteers with post-COVID fatigue underwent a range of well-established non-invasive behavioural and neurophysiological tests.

Their results were compared to those of 52 control subjects, matched for age and sex, who underwent the same tests. The tests which provided 33 sets of data included a startle reaction time test, electrocardiogram and transcranial magnetic stimulation.

Following these findings, the team now will begin testing whether the autonomic nervous system can be modulated to improve symptoms in post-COVID fatigue.

"We're examining a non-invasive method which involves clipping an earpiece to the tragus on the ear and delivering small electrical currents to the vagus nerve using a TENS machine -- familiar to many through its use for pain relief during childbirth," said Natalie Maffitt, Research Assistant at the varsity.

The study will examine the effects of the treatment by measuring markers of inflammation in the blood that are associated with fatigue in other conditions and importantly, whether it improves symptoms of fatigue.