But what happens when your fitness becomes stagnant, and you're no longer improving?
Hitting a plateau is more common than you might think, especially for beginners. Training too much in zones 3 and 4 can leave you stuck in a rut, and this can be a hard cycle to reverse. You'll have decent fitness, but improvement over time will be minimal.
If this is you, you're in luck. We asked six coaches how to help cyclists of all abilities improve their speed and fitness on the bike. Here's what they had to say: