What's driving record retirements at the US Open?

— -- NEW YORK -- Given the amount of fluid the human body discharges in extreme heat, the players at the US Open are having to think extra hard about what to pump into their bodies before and during their sometimes prolonged battles on the skillet-hot courts at Flushing Meadows.

"When you have these conditions, what you ingest is critical," No. 13 seed John Isner said on Thursday, after his second-round, straight-sets win against Mikhail Youzhny. "A lot of stuff is going to come out of you so what you put is really important -- minerals, the liquids, stuff that can keep you from cramping."

Still, even a player who performs due diligence can only control his destiny to a limited extent. Jack Sock, seeded No. 28 and one of the bright American hopes at the outset of the tournament, was up two sets to one against Ruben Bemelmans on the Grandstand, when he began cramping. Jock then collapsed on the court on the hot, muggy afternoon.

Sock had to be carried off the court by a phalanx of trainers and security, but soon recovered sufficiently to make an appearance in the player lounge.

"[Sock] sweats more than anyone I've ever seen," Isner said, "It's not a fitness thing [cramping and collapsing like that]. That's a big, big misconception. He's in very good shape. He can play 50-ball rallies if he wants to. He just loses a lot when he's sweating. His body has a deficit of whatever it is -- sodium, magnesium, potassium -- that you have to put in your body."

With high heat and humidity forecasted to return early next week, and the stakes in the tournament rising dramatically, players will be trying to do all they can to mitigate the effects of the heat.

Todd Ellenbecker, vice president medical services for the ATP Tour, told ESPN that during extreme heat conditions, players are encouraged to begin hydrating early in the day -- hours before they intend to practice or play. They are also advised to add extra salt to their foods and salt packets to their water.

This tournament got off to a rocky hot under hot and humid conditions, with a record number of retirements in the first round of play. Not all of those were a result of the 90-degree heat and humidity that descended on New York at the start of the event; injuries were the major factor.

And don't discount the reluctance of some injured players to pass up a guaranteed $39,500 paycheck (first-round loser money) by pulling out of the tournament because of an injury. All they have to do is start, play a bit and retire.

A day after the retirement theme went into eclipse on a still hot but quiet and relatively drama-free Wednesday, it returned with a vengeance Thursday when Sock pulled the plug. The pull-out was the 11th of the tournament, equaling the Open era record for the highest number of men to retire during a Grand Slam. A few hours later, Denis Istomin retired (with a non-heat-related leg injury), establishing a new mark -- this with 10 more days of play left.

The amount of time spent on court has been another factor that's stirred some controversy. A long match is an ideal incubator for injuring already sore muscles or limbs. The men play best-of-five sets, the women best-of-three. Is it mere coincidence that only two women have retired thus far, none because of heat?

The USTA has an "extreme weather policy" for the WTA, juniors, and wheelchair tennis divisions. The protocols mirror those of the WTA "heat rule," which allows the covered players to request a 10-minute break before a third set when certain temperature and humidity conditions are met. On Thursday, the "heat rule" kicked in for the women as the temperature approached 90 degrees at around 1 p.m. local time.

The men have no such rule, however.

"We follow the ATP policy and protocols," said Chris Widmaier, managing director of communications for the USTA. "It's as simple as that."

Among the Grand Slam events (which are independent of the WTA and ATP), only the Australian Open, which experiences the most savage heat, has a heat rule that applies equally to both men and women. Wimbledon and the French Open have no provision to suspend play or to provide temporary relief during scorching weather.

The ATP argues that a heat policy is not required because all tour events are best-of-three sets. The ATP board and its player representatives feel the men can handle any amount of heat over that relatively short period.

This led No. 5 seed Stan Wawrinka, who won his second-round match in straight sets (but which took him more than three hours to complete), to ask: "That's just a question I always asking myself: 'Why do the [women] have the heat rule to have 10-minutes [break] after two sets if it's dangerous, and why we don't have anything for five sets that's maybe there?' That's the question. Do we want to see something like that for the guys?"

In a surprising turn, No. 2 seed Roger Federer expressed a view that was borderline contrarian -- but not outlandish to those who echoed the refrain that the conditions just haven't been that brutal. There have been many more infernal days at US Opens in the past.

"What I don't understand, we've been here in North America for some time," Federer said after he eliminated Steve Darcis. "It's not like, all of a sudden, hot. I mean, it was more on the warmer side, but it's not like impossible, to be quite honest. Really no excuse for that.

"I think everybody should be well-prepared. I know we don't play many best-of-five-set matches all the time, so of course the body can react funny once you exceed the two-and-a-half to three-and-a-half hours of play. Mardy Fish, that's an exception. He's not been that well-prepared because he hasn't had the matches in his body."

Of course, Federer played his match on Thursday in the cooler evening. Being the all-time Grand Slam singles champion does have its advantages.