This nice little saying is one that runners know well. Running on hills can magically make you faster when running on level surfaces, because the extra work your muscles have to do to lift you against gravity makes the muscles stronger, and the payoff comes when you realise that without intending to, you are suddenly running faster on the level bits.
I had no idea that same principle applied to cycling, too.
I've done more cycling than running in the past couple of weeks, and let me tell you, going up and down the Austin hills has given my leg muscles a run (ha!) for their money; I haven't cycled on hills since before I got a driver licence. And something magical happened: I've suddenly starting going faster on the level bits. And going uphill isn't as hard as it was at first. Who knew?
Now all I need is for this little truism to kick in again for my running, and I'll be all kinds of happy.