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Power Meters Speak Truth to Professional Cyclists, but Can Mislead

His power meter, a Shimano crank modified by the German company SRM, which pioneered the technology, indicated that he had been putting out about 500 watts of energy for about two minutes.

Based on years of power data analysis, Hayman knew that 500 watts was well above the threshold where his body would go into oxygen debt and his performance would fall off.

“About 420 to 450 would have just kept me just underneath going into the red zone, that nasty point,” Hayman said Friday.

Nevertheless, he ignored the warning. “Even though it’s all there and I’m as old as I am and I know everything about power,” he said, “you still do it, you still think, ‘I’m feeling good, I can do 500 watts.’”

Hayman’s self-delusion meant that he had to back off and recover to finish the stage.

In general, however, he said power meters did not influence the regular mass stages of the Tour.

While he said that some riders might consult their power readings during a long climb, the bulk of the cyclists in the pack do not have the luxury of determining how hard they are working.

“At the Tour de France, somebody else dictates the pace 95 percent of the time,” Hayman said. “It doesn’t matter what your power meter says, if you need to follow someone over a little climb, you need to try to follow them.”

He added, “So I don’t think that racing has been totally killed by it; people aren’t just following their power.”

Max Testa, the doctor for the American BMC team, said that even in time trials, where no one else sets each rider’s pace, it can be a mistake to ride based on power.

“In the race, you normally produce more power with the same perception of effort because you’ve got a lot of adrenaline,” said Testa, who has been a team doctor for more than 30 years, including a long stint with Motorola, a former American team in Europe. “If you just do the time trial based on power, sometimes you underperform.”

As a result, Testa said that while everyone on his team used a computer during time trials to capture power data for later analysis, many riders hid their display screens with tape.

Yet Testa and Hayman both said power meters had completely transformed training.

When Hayman first rode as a professional 17 years ago, he said, he would go to a lab two or three times a year for tests to determine his threshold based on his heart rate and measurements of lactate in his blood. (Blood lactate increases when exertion reaches a level in which the body’s tissue is not getting enough oxygen to sustain it.)

Because that threshold measurement swiftly became out of date, it played little or no role in Hayman’s training. He raced about 100 days a year, and the only question surrounding his training rides, he said, was how long they would be within a two- to six-hour span.

Now, he said, “almost nobody just rides to train anymore.”

Coaches and team directors instead analyze the power data submitted by riders, usually through TrainingPeaks, an online service based in Boulder, Colo. On Testa’s team, four staff members devote much of their time to that process.

The data is used to send riders detailed training plans that carefully dictate not only how long they must ride, but how much intensity, measured in watts, they will need to exert at specific points of those sessions.

“It has been a transformative thing,” Testa said of power’s effect on training. “I’m expecting in a few years the standard of the industry is that, when you buy a bike above a certain level, it will already have the power built in — like when you buy a car, you get the speedometer.”

Since SRM popularized the technology, many companies now supply the teams at the Tour with a variety of power meters. All of them take cranks from Shimano, Campagnolo, SRAM and FSA, another parts maker, and add strain gauges and supporting electronics. All the power meter companies offer competing claims about the ideal location for the gauges and whether it is necessary to measure the power being applied to both cranks.

Power meters are not inexpensive, generally ranging in price from about $ 1,000 to more than $ 3,500.

Shimano, which dominates the bicycle parts industry, debuted its first crank with a power meter at this Tour, attracting considerable attention.

But some of the power meter suppliers at the Tour are at the opposite end of the industry spectrum. Etixx-Quick Step from Belgium uses power meters made by a tiny Canadian company, 4iiii Innovations.

Karel Bergmann, a manager from 4iiii who is traveling with the Etixx-Quick Step team, acknowledged that, price aside, power meters are not for every cyclist.

“It’s easily the best way to improve your performance,” Bergmann said. “But if you’re really just looking to get from A to B and going sightseeing on your bike, then the data isn’t that useful.”

And even for the professionals and competitive amateurs, Testa had a note of caution.

“Don’t become a victim of the numbers,” he said, noting that the brain is good at interpreting the body’s signals about exertion. “You always have to read your body. Why do you want to discharge all this very sophisticated equipment that we’re born with?”

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