Power-to-weight: ‘Lighter is not necessarily better’

Exercise physiologist Dr Jamie Pringle explains why losing weight to improve cycling performance isn’t necessarily a straightforward equation “In a straight shoot-out on a hilly climb, powerto-weight would set the finishing order. But on a rolling course, or in races where there’s just as many flat as hills, then power in absolute terms, and power-to-drag become important.

“The common factor is power, and clearly more is better. The best Grand Tour racers are rarely the lightest riders; power-to-weight is high, yes, but they need the absolute power to compete on the flat as well; and typically, although not exclusively, the bigger rider would have the muscle mass to generate greater muscular anaerobic power — important for short bursts of energy and the reason why we see one-day specialist riders like Peter Sagan and Lizzie Deignan able to mix it with the mountain goats.

“Power to weight doesn’t tell the whole story. Take the 6W/kg marker — a world class benchmark of sustainable power for the male rider (5W/kg for females) — a 80kg male rider generating 480W at his 6W/kg is a different prospect to the 55kg rider generating different 330W at his. They may ascend the first climb similarly, but how they achieve their performance on different types of terrain is different, and also in terms of total calorie turnover. A big engine needs a big fuel tank; big engines typically come with a big chassis.

“Like most things involving the human performer, the answer isn’t a simple one. While power is clearly the most important factor, lighter is not better, but neither is heavier; in fact, weight itself might not be the best divisor, when comparing different performers. Using an allometric scaling — where body mass is scaled non-linearly — can allow a better comparison across individuals of a wide range of body sizes. An index like this — power divided by mass, raised to the power of 0.67 — though less intuitive, better accounts for muscle mass and volume, and offers a performance insight that might reveal the rider’s strengths and weaknesses better than simply reviewing their average power while standing on the bathroom scales.”