It starts with a dark green box shipped full of testing supplies. Inside are vials to spit and breathe into and a monitor to wear for several days before your appointment. The leaflet told me to bring them all to a consulting room on a tree-lined street in Central London.

It’s close to the private medical hub of Harley Street, and the company’s name, Viavi, is discreetly noted above a shiny brass buzzer. Appointments can last two workdays depending on the procedures. These might include a maximum oxygen consumption (VO2 max) test, which grades your fitness level by cycling to fatigue on a bike while wearing sensors and a mask. Or you might have a brain scan, with a grandmotherly doctor (definitely out of place in the high-tech surroundings) putting sensors in your hair.

Bloomberg Businessweek