Leh, Ladakh, Oct. 3 -- Before Barun Karmakar left Mumbai to participate in the 122km Silk Route Ultra (SRU), his daughter asked him to sign a piece of paper that said this would be his last long run. She feared for his health, his well-being, in a reaction to what Karmakar was about to attempt-one of the world's toughest long-distance runs. The sales executive from GE Healthcare, nearing 50 years of age, said in response that he was willing to do anything for her, "but don't ask this of me," recounts Karmakar, seated in the dining area of Hotel Rimo in Nubra Valley, just 24 hours before the race.

On 10-11 September, Karmakar ran the SRU, which traverses terrains that range from Kyagar village in the Nubra Valley at roughly 10,700ft above...