D3:
I liked your post at some other thread (I recall calling you D3 there as well).
I wouldn't worry too much about your heart rate AT ALL. Go by how you feel and, as long as you're comfortably tired, call it a day. I see Lasse Viren did something like 15k run in 1:25 or something with his heart rate of less than 100! That's rediculous!!! I do my "easy" run with HR of about 140~150 now and I feel fine I'm 48 now so theoretically my HR should be lower (if you calculate 220 - my age). But I really don't care as long as I know that, when I'm stressed, my HR is higher even the pace is slower so I'll watch out. My resting HR does go up by 10~15% (now it's about 52) and if it goes on for a couple of days, I'll watch out. That's about an extent I pay attention to my HR.
In terms of developing your "aerobic strength"; I really doubt if anybody, even some of well-known exercise physiologists, can define what it is exactly and what you need to do to get the best out of it. Chances are; if you go slower and go further, you'll develop muscular endurace better than going faster shorter. So is it not effective workout? Some go further and slower and do great; others go shorter but faster. We are all different and all react to workout differently. If anything, I'll go with two of the Golden Rules: (1) If in doubt, do less or easier. (2) You can NOT run too slowly. Lydiard used to always said even if your HR is up to only 100, you ARE doing some good (as Viren did!) to develop your aeorbic capacity.
This being said, let me give you my honest opinion. If you are a young aspiring runner of 18-year-old (and assuming you are aspire to be a good runner), running at 11-minute-pace, or even 9, indicates your aerobic capacity is still quite low. I consider myself with not much of natural talent but I was probably doing 40~50 miles or so in high school with 100km (62 miles a week) in my senior year. The more you run, the faster you can run (because your aerobic capacity improves). But if you do it too much, you start to develop shuffling action and muscle viscosity and you stay slow. It's a fine line and you need to work very carefully so you continue to develop your aerobic capacity, therefore, your upper aerobic running speed, without losing speed.
I will continue to check your resting pulse to make sure you're building up and not breaking down. Your resting pulse should show steady decrease as you get fitter. I can't remember what mine was when I was in high school but the lowest was after I trained under Lydiard in 1985 of about 37 a minute. At the time I was doing somewhere around 90~110 miles a week at 7-minute pace comfortably.
One last thing about HR; when asked about checking HR first thing in the morning, Lydiard's favorite answer was; "It depends on who you're sleeping with." ;o)
I started out doing heart rate training but felt it was too confining. I still keep track of my heart rate but I run more by feel now and like it better.
