A shoe chafing against the ankle of one foot, and blisters on the soles and big toes of both feet, took a toll on Kingston ultramarathon runner Martin Mack Wednesday and Thursday during the fourth stage of the 30th Marathon des Sables in Morocco.

It took Mack 25 hours, 24 minutes and 12 seconds over two days to complete the 91.7-kilometre segment—a distance roughly equivalent to the distance between Kingston and Smiths Falls—of the six-day, 250-kilometre race across the Sahara Desert, .

“By far, it was the toughest stage ever,” Mack, who is competing in his fifth Marathon des Sables, wrote in an email, describing it as “92 kilometres of insanity.”

“Unfortunately words cannot do this long stage justice.”

Mack, who stands 768th in the 1,490-runner field, is now fourth among the 20 Canadians who remain in the race.

Mack dealt with the ankle issue by cutting a piece from his foam sleeping pad to make an insole to elevate his foot in the ill-fitting shoe. “It seemed to work for a while,” he wrote.

The first big climb of the stage, entirely over a rocky patch, began to chew up his feet, however, and at the 50-kilometre checkpoint, Mack decided to seek medical attention. “They taped them up and I figured, ‘I only had a marathon left, how bad could it be?’” he wrote, before answering his own question.

“Bad.”

By the next checkpoint Mack’s running was finished. “I took a nap. I got up and said, ‘I’m gonna get this done.’”

By now it was dark and Mack had more than 30 kilometres of dunes to cross to reach the end of the stage. His pace was down to a steady walk.

“The sand dunes chewed the feet and my mind,” he wrote, “(but) having rested, now my body feels good and the feet (are) ready for two more stages.”

The race ends Friday with a 42.2-kilometre stage from Oued el Jdaid to Erg Znaiqiui. On Saturday, a 21.1-kilometre “charity stage” will be run to Merzouga, a village about 50 kilometres east of the Algerian border that is the site of the largest natural underground body of water in Morocco.