IN A darkened room at the edge of downtown Washington, DC, electronic music pulses over the speakers as a crowd of mostly sweaty young women bop up and down. Candles burn at the front and inspirational slogans cover the walls. Sadly, this is not a drug-fuelled rave, but rather a mid-afternoon spin class. It is run by Soul Cycle, which promotes the idea that riding an exercise bike to loud music is akin to entering a “soul sanctuary”. The experience, which also involves awkwardly lifting weights while cycling, costs about $35 for 45 minutes. This does not deter its well-heeled customers: “Some of the women pay a lot of money to go here”, says a staff member, her eyebrows raised.

The recession of 2008 damaged many industries. One which emerged remarkably unscathed was exercise. According to figures from the International Health, Racquet and Sportsclub Association, an industry group, gym members now number 54m, up from 45m in 2009. Twice as many Americans subscribe to gyms as in the mid-1990s. Yet the population has not got visibly healthier. According to the Centres for Disease Control, a government agency, in 2013 a quarter of adults engaged in no leisure-time physical activity at all beyond the bedroom. Between 2001 and 2012, the age-adjusted proportion of the population who are obese or extremely obese grew from 36% to 41%. That increase has slowed of late, but it has not yet reversed.