Cardiac Drift

by Lars
(Norway)

Cardiac drift with increasing heart rate in sessions without an increase in speed. How to deal with it ?

"Hello Marius!

One general question about heart rate related to the sessions in your program : while training the hard sessions (i3/i4), I have noticed that the heart rate is increasing during the session, even if I am running at the same speed.

One example:
4 x 9 minutes in zone 3 on treadmill with 2 min rest. I have the exactly same speed on all the laps (starting out with 5:00 per km first 3 min, then 4:55 next 3 min and then 4:50 last 3 min)

On the first lap, the heart rate is perfect in zone 3. Also on the second. But - on the third lap, the heart rate is floating up to zone 4. On the last lap, almost the whole lap is in zone 4...

So - what to do? Decrease speed towards the end ? Start out easier, or just run on the speed and forget about the pulse?

Best regards Lars."

Answer: Hi Lars, what you are experiencing is something called cardiac drift - which is due to the relatively high temperature inside while running on the treadmill. You will see this when running outside as well if the temperature is +20-23 degrees - but to a little less degree because you'll have the wind resistance. On the treadmill you don't have that and you'll have a constant sweat factor much more so. This causes the heart rate to be "unaturally high" while the lactate/internal processes in the body is lower.

Therefore : you can allow yourself to do slightly higher towards the end of these sessions ( + 3-5 beats into Effort 4 if the session is Effort 3). You will still be in the right zone but the cardiac drift factor causes it be be "unaturally" high. That way you'll be able to increase the pace at the end as well.

Good luck with you training,

kind regards,
Marius

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