am) Met up with Jeff for a MAF run. After 7 days of no real running my HR was through the roof- I averaged 154 for 9 miles. We ran the first 3 in 21:00.. then ended up overall at 58:47. Our last 6 were at 6:17 pace. Not too bad for me.. Jeff I think averaged HR 137. The boy is fit.
Part of the reason for the higher HR after the break is due to several factors. Being rested will always yield a higher HR because the muscles are more fresh (fatigue can cause your HR to be depressed) and are able to "push" your heart. This is a pretty basic explanation. Fatigued muscles aren't as capable of pushing your cardiovascular system which doesn't fatigue in the same way.
Loss of blood volume. Capillary shrinkage. Loss of efficiency in muscle coordination which causes a need for more oxygen at similar paces before the break (this is more noticeable in swimming which requires much more efficiency). After 7 days I am also less fit, plain and simple. The basic endurance is still there but I have lost a few aspects of my fitness from strength and Vo2 to lactate threshold. All of these things will come back quickly though as I start a period of harder running.