What pace are you running your long runs? And how does that pace relate to a recent race result?
I agree with a number of posters above that you're running these long runs far too hard. It's all about time spent running rather than trying to set PB's during training. If you can't speak in short sentences during a long run, you're running too fast.
I'm really intrigued with HR ever since I got my new garmin hence my reason for starting the thread.
I did a long run on Saturday of 14.5miles, aiming to keep my heart rate in the aerobic zone. My HR never exceeded 160 (max is 194 and RHR is 57) and I averaged 8:08min/m. I hope I'm not asking too much here but would that indicate I have relatively poor aerobic system considering I can run a 39:xx 10k and a sub-19 5k ? I'm quite new to running so trying to absorb all knowledge if possible