And England, at least for a time, pondered whether its players should sleep in specially designed low-oxygen tents.

All three have won a World Cup. And in pursuit of another title, their national soccer teams have taken extraordinary measures to gird for the nearly mile-high climes of South Africa — altitudes that can affect athletes' energy, mental acuity and recovery time.

Of the nine South African cities hosting World Cup matches this summer, five are at 4,000 feet or higher. Johannesburg, where the June 11 opener and July 11 final will be contested, is the highest among them, at 5,750 feet. (The elevation of Denver is 5,280 feet.)

In the case of the United States, all three of its first-round matches are at 4,000 feet or higher, where the effects of altitude will come into play. The US squad opens against England June 12 in Rustenburg (4,905 feet), and follows June 18 with a match against Slovenia at Johannesburg's Ellis Park and June 23 against Algeria in Pretoria (4,457 feet).

US coaches considered basing their weeklong, pre-World Cup training camp in Austria, as Spain and the Netherlands, among others, chose to do.

After consulting with the US Olympic Committee's altitude-training expert, they opted to base their camp in Princeton, N.J. — essentially sea level — but travel to South Africa two weeks before their first match to give athletes time to acclimate.

The decision required as much deliberation as any tactical, on-field formation — based on a mixture of science, exercise physiology, psychology and pragmatism.

"It's more of a headache for the coaches — for me — than for the athletes," Pierre Barrieu, the US team's fitness coach, said of the challenge of developing a plan to get the Americans in peak condition for their 12-day slog of matches in Group C and, ideally, beyond.

The competitive complication is this: As the altitude gets higher, the concentration of oxygen in the air decreases. Oxygen supplies energy to the body's cells. As a result, the body works harder to keep those cells fed. The breathing rate increases, and the production of oxygen-transporting red blood cells increases.

"Being at altitude — whether it's low, moderate or high — obviously you have less oxygen available," Barrieu said, "and a simple task becomes harder."

Among exceptionally conditioned soccer players, even the slightest impairment — whether a reaction that's a millisecond slow or a barely perceptible fall-off in foot speed — can turn a match.

The US experienced the challenges posed by such elevation at Johannesburg's Ellis Park during last summer's Confederations Cup, in which they raised their international profile considerably by toppling Spain but fell flat in the finals against Brazil.

"Obviously we're all in pretty good shape," said US defender Jonathan Spector, "but when we played there last year, there was certainly a difference that you can feel. It's definitely noticeable. But in a few days you kind of adapt to it and get used to that burning feeling in your lungs."

Adds Barrieu: "We've felt the difference playing there, and unfortunately it worked against us for the final. There is a clear difference between playing at Ellis Park and playing at other stadiums."

The thinking behind the Americans' hybrid approach — train at home, but travel to South Africa two weeks early — is that athletes can train more rigorously and recover more quickly at sea level. In other words, training athletes at higher altitudes is inefficient and potentially misleading.

"The potential for hard work is not there because the players would reach the `max' at a much lower intensity than they would at sea level," Barrieu said. "And the time for recovery increased threefold because you don't have the oxygen to recover. You can hurt a player, not being able to train him as hard."

Like England, the US also considered using sleeping tents that replicate the concentration of oxygen at various altitudes. While the science is sound, opinion differs about how many hours an athlete must spend in the tent to get maximum benefit.

Hypoxico Altitude Training Systems, the US-based company that developed and markets the tents, says that six to eight hours daily is sufficient. Others believe that 18 hours a day is required. In Barrieu's view, that simply wasn't practical.

Not every person reacts to altitude the same way. While 6,000 feet may cause sleeplessness and mild headaches for some, it can trigger irrational thinking, dehydration, nausea and debilitating headaches in others.

In hope of identifying the more vulnerable members of the US team, Barrieu had the full 30-man training camp roster undergo tests in the team hotel that flagged symptoms when the available oxygen was reduced. The data weren't used to help Coach Bob Bradley cull the squad to the final roster limit of 23, he said, but to identify players who might need longer to adapt.

"There's a few protocols you can do in advance, to give this person a head-start so that by the time we get there, they would be less likely to experience any discomfort," Barrieu said.

Then there is the most low-tech protocol of all: Water. And lots of it — an intake of three times as much, initially — to stave off the dehydration of an 18-hour flight compounded by arrival in a dramatically drier climate.

Even though most players on the US squad have competed in the thin air of Mexico City's Azteca Stadium, perched at 7,200 feet, they need reminding about the importance of staying hydrated.

"All the time," Barrieu says. "All the time."