Back in January, I ran Sal's Branch and Pott's Branch trails at Umstead. It's just over 4 miles with lots ups and downs. Back then I did it in 45 minutes, with average HR of 158.
Yesterday I went and did the same run again. Weather was hot, maybe around 80 and very humid. I did it in 42 minutes, so shaved 3 minutes over 4 miles, or about 45 seconds off the mile pace. Average HR was 159. So a tiny bit higher, but at much faster pace and hot and humid weather.
Once in awhile this kind of run comes along that shows what kind of improvement I've been making that makes me feel even better about all those times spent on trails.