Twenty-five years after his diagnosis, Jason, now 66, says he’s at about 70 per cent of normal. Thin, but not gaunt, he cuts a Spartan figure in a blue pinstripe shirt and black trousers. Despite his illness, he has published over 690 scientific articles, written or edited 27 books and mentored over 150 graduate-level students; and also developed community-based efforts to prevent youth smoking and support substance abusers. “Seventy per cent for Lenny is about 140 per cent for the rest of us,” says his longtime colleague Chris Keys.

Keys and Jason helped launch the field of community psychology in the 1960s. Their goal was to find ways to empower downtrodden groups. “Community psychologists are pissed off at everything that is not fair or right,” says Jason. Pictures from that era show his transition from clean-cut college freshman to a wild-haired hippie graduate student. Understated and disarmingly tranquil, he’s an unlikely rabble-rouser. “A gentle instigator,” Keys says.

When Jason returned to work in 1991, it was only for about an hour a day at first. Over months and years, amid relapses, he slowly built that up to mornings and, eventually, to full eight-hour days. For him the key was staying inside what he calls his “energy envelope”: not overdoing it, slowly building stamina. He was always tactical, according to Keys, managing his own health while arguing that the name ‘chronic fatigue syndrome’ was tainted by stigma, and that the disease was more common than once thought and in need of much more study.

What most people don’t understand about CFS-ME, says Jason, is that even though the body is exhausted, the mind is stimulated – making sleep difficult, despite the fatigue. “I describe it as ‘tired but wired’,” he says. To this day, he avoids noisy restaurants and keeps a strict sleep schedule (in bed by 9pm) to prevent disruption. “If I’m stressed out and pushed beyond my limits, I can deteriorate very quickly.”

© Luke Best at Heart Agency

While most people balance family, personal and working sides of their lives, Jason dedicated his precious energy reserves solely to raising the profile of his disease in the biomedical research community.

He decided to start with finding out how common CFS-ME really was: “As long as people considered it a rare disorder… it would not get attention, resources or respect.” He applied for grants for four years, finally securing funding in 1995.

“Yes, it was a long battle, with the odds against us,” he says, chuckling at first, then becoming emotional as he recalls his relapse at that time because he’d used up so much energy pursuing the grant. “I was not coming into work, trying to assemble a team from home.” He lets out a big sigh.

In the end, it took ten years. Jason and his colleagues called thousands of people at random and took them through a questionnaire of symptoms, eventually updating the official estimate of the number of people in the USA with CFS-ME from 20,000 to 800,000. (Due to population growth, estimates since have risen to 1 million in the USA and about 250,000 in the UK.)

He next conducted the first non-drug trial, testing variations of cognitive, behavioural and relaxation therapies on over 100 patients. “We didn’t find a cure, but we did find a very different reaction in the US patients from what was found in Great Britain.” In direct contrast to PACE findings in favour of graded exercise, Jason found that people with CFS-ME needed to conserve their energy.

“We found that patients who were the sickest made the least improvement when pushing their activity levels,” he says. “People who had learned to stay within their energy envelope had the best success.”

Jason and other researchers studying the disease now think CFS-ME is an umbrella term that includes mild to severe cases. But there is no clear-cut way to distinguish different groups in order to identify underlying biological mechanisms or the most appropriate treatments. Even the patient groups spar bitterly over the definitions.

Jason explains that one group believes ME and CFS are different diseases – and that the people with CFS have psychological problems. Another group believes they are more or less extreme versions of the same disease. “Boy, what a clash of those two groups. They are fighting it out,” he says. “Viciously.”