Dont train solely by heart rate data

Training with Heart rate data can be beneficial for those needing a gage to bring themselves into line, and if you are finding such training is beneficial and sustainable then by all means maintain it.
However HR data ultimately is just another number to obsess about. Not as arbitrary as pace splits but can serve to distract your mind and focus on simply running and learning to enjoy it. It can also compromise your form and focus (particularly for the speed stuff) with repetitive watch checking.
HR data is also, at times, dodgy at best, and with the vast sway of sports watches it's reliability can be different brand to brand.
Ultimately though it distracts us from how we should be approaching our steady/long running and that's to feel. This way you can know for sure that you're running at a easy sustainable pace, can recover well and won't jeopardise the speed work. Running to feel will always alow for adjustments on tiredness, terrain, weather etc so it's very accommodating.
Learning to be more in tune of the rhythm and processes of our bodies and recognising when to push on, when to rest, when to keep things steady will make you one step ahead of those dependant on data. Watches and data have a place, but use them as a tool, not what forms the whole basis of your running.

Cameron Harris-Head Coach