Heart Rate Drift and HR Race Pacing Strategies
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Hi,
I renently completed a mountanous 100KM running race (Ultra Trail Snowdonia 100) followed by Supporting a friend on a ~48 Mile Mountain running challenge (the ‘Joss Naylor Challenge’).
When analysing the data following these events I noticed something perculiar:
- On the first race (hot conditions), my rate of percieved exertion increased significantly with time, whilst my pace, performance and heart rate decreased significantly (Starting around 160BPM and dropping to around 135BPM despite feeling very hard , slow and ‘suffering’).
- On the second challenge (cool conditions) my rate of percieved exertion increased with time but so did my performance (pushing and feeling strong with good normalised pace), but again my heart rate again decreased with time.
For context I’m not aerobically defficient, AET ~160BPM and Lactate threshold ~178BPM.
Is there a logical explanation to this ‘decoupling’ of heart rate versus effort? Is this an indication of poor initial pacing?
As for race pacing – is there a ‘rule of thumb’ about relative heart rate zone for pacing a hilly ~17 hour ultramarathon race? I was targeting mid Z2 for the race but found it too slow and ‘easy feeling’ and the start of the race (potentially due to being tapered or perhaps adrenaline?) so I moved nearer to upper Z2 initially, but i did not perform optimally during the race, partially due to the hot weather but I’m wondering whether it was also due to sub-optimal pacing at the start.
Thank you in advance,
Regards,
Mike
Mike:
Great questions and I am preparing an in-depth article that will touch on these subjects. But here is my take on what you experienced.
First let me say that pacing in an event eating many hours is much harder than pacing in a short race. In a 1okm race if you are running a few seconds/km too fast you will feel it in within a few minutes and the feedback will tel you to slow down before too much damage is done. So you get almost immediate feedback about your pacing. In an ultra the effort should be so easy for you in most of the race that you will be tempted to push too hard in the early stages. But, a pacing mistake of say 1min/km in the early stages will not make itself known until hours later, late in the race when it may force you to slow by many minutes/km.
Its sounds like you might have done just that kind of mistake in the 100k race. But the heat complicates things a great deal. It might make you feel a little better to know that even the top pros I coach see a steady drop in HR during the race. For instance: a 1 hour 17% climb early at UTMB HR can be 150 at an RPE of say 5. A similar 18% climb late in the race might only see a HR max of 130 and have an RPE of 7 or 8.
In the 48mile pacing you probably were not as jacked up and excited so controlled the pace better. Any we can’t discount the cooler conditions. The HR decline is again quite normal.
I hope this helps,
Scott
Hi Scott,
Many thanks for your explanation above. It is much appreciated! It’s good to know that pacing longer ultras is tough even for the pros and that the HR drift is not uncommon. I think that what makes it difficult is wanting to know that you’ve given everything and ran as hard as you could rather than coasting, which requires a very fine line between going too hard and pacing ‘just right’.
Next year’s aim will be some heat acllimation prior to the race together with maybe a slower start and some time targets for the race sections based on recces. Whether I have the self dicipline to maintain a seemingly stumblingly slow start pace is another matter and is yet to be seen!
Thanks as always for your continued sharing of your knowledge!
Regards,
Mike
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