Running

Right, I'm extremely ignorant of these things, so someone please correct this (with reference to the run linked below):

HR average is 166 bpm, but first half it's below that and second half of the run its 170+.

It seems to me that I'm like an engine running out of revs- I need to either raise my rev limit, or produce the same power at lower revs, if that makes sense?

Today I think I could have gone faster for longer if my heart rate had stayed at the halfway rate rather than climbing.

http://connect.garmin.com/activity/90103577

The basic physics of running dictates that your heartrate will be constant for a given workload. Regardless of how long you have been performing that work.

The biology of running dictates that as your muscles become fatiged, you will run less efficiently. You will also lose blood volume, if you dont drink enough water. This reduction in blood volume leads to a notable increase in HR.

For once I'm not just rehashing stuff that I seem to remember reading. I've done experiments on this myself. I have run 15km on a treadmill, with constant HR when hydrated, and a HR which started to increase after 9km or so without hydration*.

So you either need to carry water, or your muscles are fatiging, and you need to HTFU.

(*yes I have the immunity to boredom to do this)