While we admire John Isner winning the longest-ever tennis match against Nicolas Mahut—70-68 after 11 hours over three days, and 7 hours five minutes for part of the fifth set alone on the second day in 81 degrees—it’s the fitness, endurance and determination to keep playing by both men that impresses me the most. Even if Isner was looking and acting like a zombie with no idea of where he was and what was happening.

John Isner

How did they survive it? Here is what : Lauren La Rose wrote for The Canadian Press:

…So just what would it feel like to play that much tennis over the course of three days? Imagine expending the energy equivalent of running two marathons, says Brendon Gurd, an assistant professor in the school of kinesiology and health studies at Queen’s University.
Gurd says the intensity of tennis is probably on par with a light jog.

“It was separated by two nights, but they essentially jogged for 11 hours total, so it’s a huge demand,” he said from Kingston, Ont.

“What goes along with that is as they’re exercising, they’re using stored fuels, so they’re using carbohydrates stored within their muscles, they’re using fat stored in their fat cells, so a lot of that as you continue to exercise will become depleted.”

Lance Watson of B.C.-based LifeSport, who has been coaching triathlon and distance runners for more than 20 years, including Canadian Olympic triathlete champion Simon Whitfield, said the big difference with tennis is that it’s a stop-and-go sport.

“Eleven hours of that would just be brutal because there would be so much muscle teardown,” he said from Victoria.

“I guess for the regular person if you could imagine doing sets of jumping jacks on and off for 11 hours I think that would be a comparison.”

Nicolas Mahut

Gurd said in a rough estimate, the players were probably burning somewhere in the neighbourhood of 600 to 700 calories an hour, but those figures could potentially be higher.

Both Gurd and Watson said staying nourished and hydrated while competing is critical.

Watson said in working with Ironman athletes, a huge part of their preparation and training is becoming systematic about the way they consume calories and fluids. For example, many will set their watches to go off every 15 minutes to ensure they’ll remember to eat a certain amount of carbs, he said.

“They would be probably preparing their hydration and their nutrition for their typical length of match and they wouldn’t have probably preloaded and kept the calories coming in in anticipation of that kind of an endurance match.”

Gurd said Isner and Mahut were probably eating as many carbohyrdates as possible to stay fuelled, while also guzzling Gatorade, which is source of both carbs and hydration.

While not all that important during a workout, having protein following exercise can help resynthesize depleted carbohydrate stores, Gurd said.

He said lactic acid buildup likely wouldn’t have been a huge factor for the players since it accumulates and clears very quickly from the body when doing high intensity exercise. However, the main thing they’re likely experiencing is sore muscles as a result of overuse.