New Delhi, Oct. 24 -- Inside Hall 6 of the Nesco exhibition centre in Mumbai, the corridor throbs with activity on a mid-September weekend. Hundreds of annoyingly fit-looking people, most in fitted T-shirts, some men shirtless, walk around purposefully. Some pose in front of Hyrox signboards, flexing their muscles, grinning with accomplishment as their participation is registered for posterity.

Past the buzz of people in the hallway, past a door and inside the 15,000 square metre main hall, where the fitness event is underway, pumping music blares on speakers as participants run around in circles. A bridge takes spectators over the runners and to a central atrium where several others sit on rowing machines, push weights, pull weights, gr...