What Cardiac Drift is and How it Affects your Indoor Cycling

Photo of author
Written By James Quilter

Passionate cyclist and content creator

A few years back, we conducted a Twitter survey and gathered responses from 100 Zwift and Sufferfest cyclists on their biggest complaints about indoor cycling.

Sweat came out among the highest.

The problem was getting covered in the stuff. And let’s be honest, even in the coolest room, or with a specialist indoor cycling fan, you soak out a towel pretty easily.

But getting wet is not the real issue.

Nor is it the damage the salt can do to your components, although that’s an issue too.

The main problem is that it can cause cardiac shift. Here we will look at what it is, how it affects you, and how to avoid it.

Watts tied to performance

TLDR; if you are on Zwift, Sufferfest, Trainerroad, or just plain indoor cycling to your smart trainer’s app, then you need an indoor cycling fan and proper hydration. Simples.

At the end of the day, body heat can directly influence how much power you can knock out on the bike.

Keeping cool can give you a competitive advantage.

The reason for this is simple.

As the body removes heat from the core during exercise in the form of sweat. The idea is it sits on your skin and evaporates as you move along. This then cools you down.

The problem is if you are on an indoor trainer the sweat and heat just stays there. Worse still losing fluid can cause the blood to thicken, which forces the heart to work harder to achieve the same output. And you hit a downward sprial.

So unless you cool down and replace the lost fluid your body will be unable to keep up. Wattage will go down as a result.

It is estimated this can hit you by up to 30 watts.

Cardiovascular drift

This is called cardiovascular drift.

In a nutshell, it increases heart rate and core temperature, and body fluid reduction.

The increase in core temperature is accompanied by an increase in the heart rate. When this happens the body raises your blood flow near the skin in an effort to control the situation.

However, this removes blood flow from the muscles that are already at capacity.

plasma-reduction What Cardiac Drift is and How it Affects your Indoor Cycling
Percentage reduction in Plasma volume during moderate cycling exercise (Plowman, Smith; Exercise Physiology for Health, Fitness, and Performance)

No fan + no water = an increase in heart rate

In the early 90s, researchers carried out an experiment to document the rate of cardiac shift. They compared two groups of ‘endurance trained’ cyclists over a two-hour period in a room keep at 22 degrees centigrade – one group who used fluids and one who didn’t.

A 10% increase in heart rate was measured in the group without fluids.

The cyclists who drank enough liquid to match what was lost through sweat rate increased their heart rate by only 5%. So half the drift is caused by dehydration and sweat.

As a result, if the amount you sweat can be reduced through cooling the body then a fan is the best possible solution.

Although this is about hydration the link between that and a fan is clear. Put simply the air from the fan will cool you down.

What can you do to minimise it

Besides keeping cool. Drinking, and switching on the fan.

Stay aware of it. Keep an eye on your heart rate monitor to against your wattage on Zwift or whatever indoor cycling application you are using.

Concluding thoughts

We ride indoors to keep in shape and make ourselves better cyclists. Whether you want to race on Zwift or train for the Etape.

An easy way to replicate the outdoors is to replicate the air that flows around you when you are riding. And do it properly.

So get the most out of that training. Make sure your body is working the way it should.