Watts per kilo. It's the number that dominates cycling conversations, and for good reason — on a climb, it's the single best predictor of how fast you'll go. But it's also the number that leads more riders astray than almost anything else in the sport.
Let me put this in perspective. If you weigh 80kg and hold 260 watts at threshold, your power-to-weight ratio is 3.25 w/kg. You want to get that to 3.5 w/kg. You've got two paths: lose 5.7kg while maintaining 260 watts, or gain 20 watts while staying at 80kg. On paper, both get you to the same number. In practice, gaining 20 watts through structured training is far more sustainable and carries none of the risks that come with aggressive weight loss.
I've watched riders — good riders — wreck their seasons chasing a number on the scale. They cut calories during a build phase, lose muscle along with fat, can't recover between sessions, pick up illnesses, and end up slower than when they started. The power-to-weight ratio improved on paper because they lost 4kg, but the power dropped by 15 watts and they couldn't hold it in a race.
The other thing that needs saying: power-to-weight is almost irrelevant on flat terrain. On the flat, you're fighting aerodynamic drag, and that's determined by your frontal area and position, not your weight. A bigger, more powerful rider will be faster on the flats even if their w/kg is lower. So if your goal events are flat sportives or time trials, stop worrying about your weight and work on your position and raw power.
For hilly events, yes, watts per kilo matters. But increase the watts first. Manage your weight through sensible nutrition and consistent training, not deprivation. Your body is an engine — starve it and it produces less power.
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