Joe Friel's Blog is for the serious endurance athlete who wants to stay current on the science and art of training for sport. Here you will find Joe Friel's thoughts and ideas before they are published anywhere else. You may also visit www.TrainingBible.com for more detailed and free content.
Here you can see a WKO+ running file for one of the triathlete's I coach. What you see is a red heart rate graph and a blue speed graph for a stand-alone half marathon (i.e., not part of a triathlon). He did what nearly all runners do--went out too fast thinking he could put time 'in the bank' for later on when he would slow down. You can see the blue line dropping until near the end as HR remains steady. What he actually did by going out so fast was to create enough acidosis-related fatigue that he was forced to slow down later. I find pacing one of the most difficult things there is to teach runners. I also learned from this file that his run FTP (functional threshold pace) was set too low so I bumped it up a little bit (faster pace) in his file. This race came at the end of the season so he was in good shape (high fitness) and well-rested (high form/low fatigue).