When you work on one aspect of fitness, others will suffer. No doubt about it.
Here is a good representation of what is happening. The corners of the triangle represent speed, endurance and power. The area of the triangle represents the total amount of fitness
Work on speed – endurance and power will suffer. Work on endurance and power, speed will suffer. Alternatively, the triangles might represent hill climbing, sprinting, and TT’ing. Work on hills, sprinting and TT’ing worsens. Work on TT’ing, hill climbing and sprinting diminishes. You get the point. Training specific aspects of fitness decreases other aspects of fitness.
So how do you get good at everything? Well, there are two training concepts – general fitness and specific fitness. Fitter riders have bigger triangles. However, even the best riders will still experience the same triangle effect. Pull on one side of the triangle to make it bigger and the other side gets smaller. The best sprinters at the TdF are not good time trialists or hill climbers (this is all relative to the best bike riders in the world of course).
You can see how this ties in with my last post. Pick one thing, excel at it, and work to make those other parts of the triangle as good as you can without sacrificing the stuff you’re good at. Picking out your strengths and weaknesses is the first step.