Aman Awasthi, 61, moved to Delhi in 2004. After developing a heart condition, his doctors advised a strict diet and regular exercise. So Mr Awasthi made it a point to walk for 30 minutes and top up the hour running every morning. "How ironic that now doctors are saying don't run. It will turn out to be unhealthy. This is the price of retiring in a city," he said. On a sunny but somewhat foggy morning, a group of Lycra-clad runners stretch their hamstrings in Delhi's Nehru Park. Sporting yoga mats, water bottles, breathing masks and heartbeat monitors, the group is meeting for their weekly training for the Airtel Delhi Half Marathon.