When Harry Leeming developed symptoms of long Covid, he found the lack of understanding of the condition alarming. “They became so severe that I went to A&E and I was turned away, being told that I had anxiety or that it was deconditioning,” he said. “It’s been very frustrating to not be taken seriously as a patient.” Now, he’s hoping to help those living with the condition by creating tools to track symptoms and manage activity. The app, Visible, is currently available in beta form, and is also geared towards people living with conditions such as Myalgic encephalomyelitis, also called chronic fatigue syndrome (ME/CFS). Leeming, co-founder and CEO of Visible, said the goal is to help those with these conditions manage their illness – such as the worsening of symptoms after exertion. “It doesn’t happen immediately after you have exerted yourself. It actually happens hours or even days later when your symptoms get worse. So because that feedback loop is so long, it’s very difficult to tell if you’re overdoing it,” he said. “What we do is we shorten that feedback loop so we tell you much sooner when you need to slow down and when you’re over-exerting to reduce the chance of having a symptom crash.” Leeming hopes the app will also help to shine light on “invisible” illnesses. “I think the biggest issue with long Covid and these diseases like chronic fatigue syndrome is the lack of a diagnostic test – and in the eyes of the medical world, if your tests all come back normal and then you’re seen as a psychosomatic,” he said. “Really what we’re doing with Visible is we’re building the ability to measure these conditions [using] digital biomarkers that will help make these conditions visible – visible to patients so that they can manage their own condition, visible to clinicians, so they can recognise them, and visible to research as well so they can understand them.” In its current, free, form, Visible is somewhat basic, offering users a morning and evening check-in where symptoms, sleep quality and menstrual cycle can be logged, while the biometrics of heart rate and heart rate variability (HRV) can be measured by placing a finger on the back of the smartphone’s camera lens. “Research has shown that HRV is reduced in people living with long Covid and ME/CFS, and that it can be a reliable predictor of fatigue severity,” the app notes. After a few days the app starts to offer a “pace score” to help guide exertion levels, while users can also explore trends in their symptoms. “We overlay them essentially on graphs next to the biometric. So you can spot patterns in your illness and then make changes to your lifestyle,” said Leeming. Leeming, who was an avid cyclist and climber before developing long Covid, added that early next year the team are planning to roll out a subscription service involving wearable devices to track further metrics. But unlike fitness apps, which encourage users to do more, Visible will help people pace their activity. “In the future we do want to move to predicting symptom flare up so that we can tell people earlier and give them a larger envelope in which to exert themselves,” he said. The team, who have gained $1m (£847,000) of funding from healthcare funds and investors, have been working with researchers and medical professionals to produce the app, and are hoping to share anonymous data with scientists to fuel new insights into invisible conditions. Dr Viki Male of Imperial College London is currently in the process of gaining ethical approval and funding to use data from app users, as well as a control group, to study potential relationships between long Covid symptoms and different stages of the menstrual cycle. “It can be very important for people who’ve got long Covid because if we know that hormones affect your symptoms, that straight away gives us the possibility of using things like hormonal contraception to maybe make them less bad,” she said. Leeming suggested the app may also bring other benefits to users. “Having objective measurements of your condition gives you a lot of validation as to how you’re feeling … and also feeling more in control of your illness,” he said. “You have so many questions about your body, and we help to answer those.” Claire Higham, of the charity Long Covid Support who herself has the condition, welcomed the app, saying while energy management is crucial for those with long Covid, many have wrongly been told to exercise. “An app that can guide and make visible this problem for patients, family, doctors and society is a step forward,” she said.