Hyrox, CrossFit, ultra-endurance trail runs – highly challenging activities such as these are popular in Hong Kong. The appeal is obvious: taking part in them makes ordinary people feel heroic. And in a city hooked on achievement, they have become a kind of status symbol. But the popularity of such events is causing many Hong Kong people in midlife to be stung by what might be called “extreme fitness FOMO”, or the desire to do more than their bodies, schedules and recovery capacity can sensibly...