The zones should be treated as a guide only - we are all unique and the general guidelines you see for heart rate zones out there are just that - general and guidelines.
If you read anywhere that you must stay at an exact heart rate or an exact heart rate intensity then take that advice with a big grain of salt and modify it based on all the other signs your body is giving you.
Your aerobic zone might be anywhere from 65-80% , threshold anywhere from 80-95% and VO2 anywhere from 90 -100 %.
Re running hills , average heart rate isn't the main thing. You could go way over your aerobic zone going uphill and then way under going down but averages out in the zone. What you have effectively done is a tempo session and a long warm down. That's not an aerobic session just because the average is in your aerobic zone .
Heart rate is to the be all and end all of training intensity , its a guide and should be used as just that unless you have a LOT of experience and are running a flat course.
So if you want to do an aerobic run , when you get to a hill , if its any more that a very short one slow down , to a walk if you have to because if you don't you aren't training your aerobic system .
Each run should have a purpose , if the purpose is to develop aerobic fitness then you should stay aerobic .
Don't make the mistake of thinking if you lost 3lbs of weight you should have drunk 3 lbs of water. You should NOT finish a run with the same weight as you started, that's a sign of over hydration which has potentially worse side affects than under hydration.
Elite marathoners finish the race in the most dehydrated state compared to all other runners and are often 5-7% lighter at the end of a marathon.
There is not even any research to show that core exercises enable to maintain correct posture for running longer.
I agree that being able to maintain good form and posture will help to run faster for longer but there is no evidence that tradional core exercise do this.
There is actually very little evidence that core exercises improve posture full stop let alone during a dynamic activity like running.
Core exercises do help but if and only if the exercises are specific to runners. Since most coaches and trainers dont understand how the core works when we run its not surprising they trot out the same old planks , side planks , crunches etc.
A far better series of exercises that are running specific can be found here
I still argue that it's a waste of time. There is no research to suggest that it has any benefit and plenty of sound arguments it doesn't .
I agree runners need strength and I argue that core training exercises should be dynamic , three dimensional and performed standing up. In fact the American College of sports medicine in 2010 said exactly that.
There are plenty of better ways to train the core than the way 99% of people do it now.
Traditional core exercises do improve core strength ( all the research I have seen agree with this) BUT improved core strength doesn't equal improved running performance.
In the same way that people who can do a heavy squat in the gym aren't the best runners. There are thousands of people who can squat heavier than Mo Farah in the gym but can't run sub 4 min k's let alone sub 3 minute.
Improved strength doesn't equal improved performance , improved SPECIFIC strength equals improved performance. Current core training exercises are a long way away from being anywhere new specific.
Years ago we all thought static stretching was the thing to do before we run whereas now we know its actually detrimental. In a few years time exercises like cruches and plank will be looked upon the same way.
We can either bury our head in the sand and ignore the scientific research and sound arguments that explain why planks and crunches are a waste of time or move forward or change the way we work our core and make it more effective for runners.
Just because Mo did core training doesn't mean it's worth doing. It wasn't the only think Mo did differently to make him the champion he is.
I'll say it again there is NO evidence that planks and crunches improve performance in running and the idea that it would goes against basic biomechanics and physiology.
One of the fundamental rules of exercise is the specific adaptation to imposed demand , which basically says
The benefits of an exercise are limited to the loads used, range of movement, joint angles, body position and speed of the movement.
Planks and crunches use slow movements, whilst lying on the floor not moving arms and legs with very little range of movement.
Running is performed standing up, dynamically, with arms and legs moving in opposite directions .
Nothing like each other hence no benefit.
This is not my view its the view of the American College of Sports Medicine and numerous other researchers.
There are far more effective ways to train the core and I argue that if researchers show that traditional core exercises don't improve performance then they are a complete waste of time.