Hi Putnid,

A humble recommendation to read Phil Maffetone's book on endurance, and also consider his latest book on heath and fitness. His Maffetone method, of training systematically with a heart rate monitor is life changing.

http://www.amazon.com/Big-Book-Endurance-Training-Racing/dp/...

Maffetone was a trainer to some of the best triathletes, including Mark Allen. However, his advocacy is useful for anyone who wants to practice a healthy lifestyle. Once I got used to training with the HR monitor, I could run 10 miles and still have plenty of energy. I stopped looking at the clock, and instead followed my heart.

Just a suggestion,
Iain