April 23, 2012

Heart rate drift and pacing

So common wisdom tells us that to race efficiently, shoot for negative splits.  In it's simplest form this means to run the second half of the run faster than the first.  It makes sense and I had never given it much thought beyond - "I'll give that a try".  Now, try as I might, I am not good at this.  Generally my best efforts result in even pacing throughout an event whether it be a 5k or a 13.1.  For me, every race has gone something like this:

Mile 1:  Gotta get out of the crowd.  Now I am going to fast, won't be able to maintain this for the distance.
Mile 2-?: Gotta slow down!  I think I got it now.  Drink something.  Keep running.
Final Mile:  Why in the hell is this so hard all of a sudden.  How is my heart rate still rising?  Maybe I'll just die here...

Turns out that at least one (of the many contributors) to my problem is heart rate drift (HRD).  HRD is the phenomenon endurance athletes experience during training (or for myself more prominently in a longer distance races) as a result of continued exertion and progressive levels of dehydration.  In short, my understanding is this:  as we lose water our blood becomes thicker.  Our hearts then have to pump faster to move that blood around enough so we don't die.  It looks like this:
This is a heart rate chart from a recent fartlek workout I did.  The initial plateau is my warmup, somewhere around 9:30/mile.  Each spike is then a 30 second "sprint" at a 6:15/mile pace followed by a rest of 5 minutes at that 9:30/mile pace.  The concept of HRD clicked home for me when I recently looked through my training log and found this little example.  Each interval pushes my heart rate a tad higher with that last one hitting about 90% of my max heart rate or so.

So now I have a bit more of an understanding of what pacing means to me.  I have to keep it slower at the start so that I can factor HRD into my final mile.  I am going to be pushing a higher heart rate at the end of a run at a given pace than at the start and there is science telling me why it is so.  Hydration and pacing matter to race the best race (not to mention a lower blood/cake level, but that is a different post all together).  This is a goal now.  Getting pacing down and start truly figuring out why my actual hydration needs are.

On a side note, IT Band is feeling much better.  Pulled off a 4 mile hilly run in Grand Rapids over the weekend with no pain.  This was my first run not on a treadmill in over a month and the first time I have attempted any sort of hills in quite a while.  Felt good and strong.  Eyes towards August now and the Speedy Chub Relay at Steelhead.

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