Pace vs HR

The faster you run the higher your heart rate - this much is obvious. However, it's useful to know the exact relationship between pace and heart rate. In most people an increase of 10 bpm will give an increase in pace of 30-40secs/mile, although as we'll see it's not a simple linear relationship.

Following on from Wednesday's pace test I thought I'd re-run a mini test at a slow pace to check whether my pace/HR relationship is still what it used to be.

Here's a short 2-lap test I ran this morning:
7:30am 22nd Feb 2008 - 3 miles slow pace 2x1.5 miles continuous:

Lap time	Heart rate	Pace
13:26	115bpm	8:58/mile
13:26	115bpm	8:58/mile

I also wanted to make this my first proper double training day (I've been doing morning gym sessions with some treadmill running, but not run 2 pure running sessions in the same day in this campaign as yet), so I decided to re-run the session this evening to see how my heart rate looked:

5:00pm 22nd Feb 2008 - 3 miles slow pace 2x1.5 miles continuous:

Lap time	Heart rate	Pace
13:27	112bpm	8:58/mile
13:24	112bpm	8:56/mile

The temperature for both sessions was within 1°C and the weather conditions were virtually identical.

The results are interesting: a 3bpm difference is at least 10secs/mile! That's a minute off your 10k time. This confirms what I suspected: I've read that your performance is better in the evening when your body is at its proper temperature and you're at your metabolic peak (around mid-afternoon in fact). Food for thought next time you are choosing whether to do that 10k at 9am on a Sunday or have a go at the Wednesday evening 10k for your PB attempt!

I digress though. We now have 2 (evening) data points:

Pace	Heart rate	Speed
8:56/mile	112bpm	6.72mph
7:24/mile	141bpm	8.11mph

So there we have it: 32secs/mile for every 10bpm rise in heart rate.

Of course it's not that simple. It never is, is it? I said earlier that it isn't a simple linear relationship. You'll notice in the table above I've added a column for speed, a measurement we runners rarely use. This is because for good physiological reasons heart rate is proportional to speed while we are running aerobically. The faster we run, the more power we require, in a simple linear relationship. The extra power requires extra oxygen, and this is delivered by a higher heart rate - all in simple linear relationships to the speed.

So lets add a couple of extra points to the above table:

Pace	Heart rate	Speed
8:56/mile	112bpm	6.72mph
8:20/mile	122bpm	7.20mph	Interpolated
7:52/mile	131bpm	7.63mph	Interpolated
7:24/mile	141bpm	8.11mph

So, assuming those interpolated points are correct (theory says they are), then my pace increases by 36secs/mile for every 10bpm at the bottom of my range, and 32secs/mile for every 10bpm at the top of my range. (It will be interesting to re-run the test to confirm these paces/HRs.)

So why is this important? I know that I can run a 10k at 156bpm when fresh. This should equate to a pace of 6:47/mile or a time of 42:13. Oh well, I'm not on PB form yet, some 50secs short in fact. Let's hope the taper works wonders, because the science doesn't lie!





Probably.