Most people thought human-powered flight was impossible, so British industrialist Henry Kremer decided to put up 50,000 pounds to prove them wrong. It took almost 20 years, but finally, a 70-pound American aircraft named the Gossamer Condor finally claimed the prize in 1977. At the controls was 24-year-old Bryan Allen. An amateur cyclist and hang-glider pilot, Allen had prepared for five months by putting himself on a strict diet and hitting the gym regularly. The results were spectacular: He lost 15 pounds without sacrificing any of his pedaling power [source: Wahl]. On race day, at a lean 6 feet and 145 pounds, Allen piloted the Gossamer Condor around the mile-long course to victory. It was a triumph for aviation -- but also for the power-to-weight ratio.
Just as you need a good power-to-weight ratio to fly a human-powered aircraft, so too do you need it to reach the pinnacle of endurance sport. In any triathlon, serious contenders have to show up with bodies that are a near-perfect balance of strength and weight. There's not an Ironman winner on the planet who hasn't spent days and weeks agonizing over his or her personal "ratio."
For running, every extra pound can cost about two seconds a mile [source: Friel].
Over an entire marathon, that means a loss of almost half a minute. Which, if you're running in a world class event like the New York City Marathon, could mean the difference between first and fifth place.
For cyclists, hill climbs will be the ultimate proving ground for your power-to-weight ratio. If your ratio is poor, you may be able to keep to the front of a pack using your wits alone. But once it comes down to pumping your way up a steep grade, you'll start to notice the difference. A classic example is that of 1996 Tour de France winner Bjarne Riis. Years before, Riis had been little more than an underdog rider. But thanks to a strict coaching regimen, Riis was able to drop 15 pounds while also ramping up his pedaling power. By the time the Tour started, he had miraculously achieved the ideal ratio of 3 watts per pound.
Riis was up against Spaniard Miguel Indurain, who was fighting for his sixth consecutive Tour de France win. Indurain was much more powerful than Riis; when pedalling all-out, he could generate 550 watts [source: Kessler]. Riis could only manage 480 watts, but he was a full 26 pounds lighter than Indurain. In the end, Riis' power-to-weight ratio was only fractionally better, but it was enough to put him ahead of Indurain and into the lead [source: Kessler].
Generally, in cycling, the ideal hill climber will weigh about two pounds for every inch of body height [source: Hughes]. If you're 5 feet 9 inches (the average height for a U.S. man), that means you should be tipping the scales at 154 pounds.