Right, yesterday I did a PB at the park run (25m30s), a friend of mine was taking part in a race today, so he didn't want to run fast in the park run and so said he would act as my pace maker, hence my PB, he runs this park run, which I am reliably informed to be one of the hardest in the country, in 20m 30s, he's the same age as me 52. His pace as you can imagine was considerable by my standards and on one particular part of the course I said to him "I need to catch my breath" and walked for around 30 seconds on the hill and still did a PB. Now tonight, I thought I will run the park run course, take it easy and try to run the course without walking anywhere, this I did, but did it in 28 minutes 30 seconds. The question is this, am I lacking stamina to complete the course at a faster pace without walking anywhere, yesterday's pace was 8 minutes 13 seconds per mile, or am I lacking leg strengh/muscle to be able to get up the hills comfortable and maintain a decent pace, tonight's pace was 9 minutes 10 seconds per mile. If I drop the pace I can run the whole course, if I up the pace I struggle with the hills. Yet surprisingly, even though I walked for 30 seconds yesterday, I still set a PB. What is my area of weakness?