heart rate training

I must have been carrying some doubt about the effectiveness of the heart-rate limited training I have been doing the last five months. I say this because of the relief and delight I have been feeling the last couple weeks as my training plan has moved into speed work.  I can run and cycle a lot faster and more comfortably than I could last May when I started training for the middle distance tri at the end of this month.  I had an insight while riding today as I road past the tulip bulb fields I visited in May. Back then, they seemed so far away - I reached them on a ride which was then my longest ever.

Today I found the fields laying fallow. I thought about the waiting time after something is planted. Waiting for it to grow beneath the ground until it blooms.  I thought about my worries during practice sessions where the heart rate limit required me to keep a slow pace.  I was waiting for me to grow. I wouldn't criticise a bulb field for not having flowers in September or February.  Why would I feel concerned about a slow pace during training?  I don't need to bloom except on race day, after I've carefully tended my fields and given myself time to grow.