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.
I'm often asked what shoes I personally recommend to help stay injury free while running (on the 100 day plan) so I'll add a little bit about it at the end of these Q and A's.
Good shoes are crucial if you want to stay injury free during your marathon journey. In general, the best is to find a shoe that fits your feet according to your foot type.
However, these three shoes will do an excellent job with their mild correction - and will work for most runners :
1. Asics Gel Kayano (click for zappos reviews for other runners views)
The legandary shoe from Asics. You cannot go wrong with this one.
The most sold running shoes ever - and by every model seems to get better and better. About the same weight as the Kayano but the fit is a little bit different.
The 2150 is a great alternative for the faster work you'll be doing in the 100 day plan. It is one of the few shoes that "feels" like a lightweight one but at the same time has more than enough stabilty to prevent injuries with the marathon type length of some of the interval sessions.
A tips for international (non-US) runners : check out roadrunnerssports.com :
Example : Asics Kayano (RoadRunnerssports) they ship worldwide and it can really save you some money on your shoes.
I'm often asked what shoes I personally recommend to help stay injury free while running (on the 100 day plan) so I'll add a little bit about it at the end of these Q and A's. 
