You know the drill: it is Sunday morning, the sun is shining, and you have a targeted 90-minute Zone 2 training session scheduled. Just spinning the legs, keeping your heart rate or power strictly within the lines. The goal? To train your fat oxidation and build that unshakeable aerobic base.

But then, halfway through, that steep railway bridge appears. Your cycling ego starts to tickle. You push through, click into a heavier gear – and bam, you fly up. Heart rate and power skyrocket out of their tight boxes. Reaching the top, you ease off the pedals, your breathing calms down, and your watch quickly signals you are right back in Zone 2.