Cardiovascular Drift

Why is my power staying steady, yet my heart rate continues to climb?
Most of us have experienced this first hand.  This is known as cardiovascular drift or heart rate decoupling.  But why does it happen?  Should we care?  If so, what can we do to help mitigate it?

Although some athletes may interpret this higher heart rate as getting a better workout, according to Dr. Ed Coyle of the University of Texas, this extra stress is not beneficial  It is a negative type of stress.

Take a look at the graph from one of my athletes doing some long (15 minute) sweet spot intervals:

Key:  Red:  HR in BPM;  Purple/Pink:  Power in Watts;  Blue:  Target Intensity in Watts

For each interval the power was very steady as you can see, but their heart rate rose over each successive effort.  By the numbers, interval #1 was a 144 average HR, #2 was 151, and #3 was 155.  An 11 BPM jump from the first to the last.  Part is due to fatigue, but this workout was done indoors and heat played an issue.

That's a great graphical example of what cardiovascular drift looks like using data.

​So what's the deal?

If you’re not interested in reading the article or listening to the talk, the biggest take-aways are:

• Come into your exercise well hydrated.  This means consistently hydrating on a daily basis, and really focusing on the days and hours before a hard and/or hot training session or race.
• Keep yourself as cool as possible during exercise.  This is obviously very important and often challenging when riding indoors.  If possible, choose a cool location in your house and setup as many fans as possible.
• Stay hydrated during exercise.  While there is a limit to how much fluid per hour our gut can process, it’s worth it to take the time to learn about hydration and the use of electrolyte replacement drinks. For those long indoor sessions, be prepared with plenty of bottles all made up ahead of time.  When you’re outside training, don’t be hesitant to stop and refill your bottles on regular intervals.

What about heat adaptation?  Science has shown that our bodies actually do adapt to the heat with physiological changes, but purposely making yourself hot during exercise can be detrimental to the quality of your workout at best, and possibly dangerous.  Better to stay cooler and nail your workout.  I’ll take a look at heat adaptation in another post.

​Here are two great resources that dive into why this happens, why  it is indeed negative, and what you can do to help minimize your CV drift.

Fasttalk Labs Podcast:  Cardiovascular Drift with Dr. Ed Coyle
 
Polar Article:
 
And if you really want to nerd out:

Science Direct

So while getting your heart rate up during exercise is often the desired response and a good thing for our fitness development, take the necessary steps to avoid that cardiovascular drift.
 
Have you ever experienced CV drift?  Have you learned any tricks for staying cooler while riding indoors?  Post up questions and comments below!

Drink up and get that fan firing!
Coach Brian

I have to do most of my training indoors and the intensity of the intervals varies a lot. So my absolute essential item has become the Wahoo headwind fan, which blows a narrow column of air at up to 25 mph. Best of all it adjusts the fan speed based on my heart rate monitor, or you can choose to have it adjust based on power. No more getting on and off the bike, sweating and freezing. I keep the fan behind me as a tail wind, which I find much more comfortable. Definitely worth the investment.
​~Rebecca