During the lockdown phase, many cyclists lived off a nightly diet of lung-bursting Zwift races and high-intensity intervals on the smart trainer. And as many of us reap the rewards of record 5-minute power outputs, some forget that our endurance base is the foundation upon which our lockdown gains stand. As with any brittle foundation, the house will only come crashing back down to earth unless we prop it up with something solid.


There’s an old saying that states that summer races are won with winter training. While many of us trained solidly during the winter, we were later robbed of our endurance gains during the spring. But while this reverse periodised approach may work for those targetting shorter events, it’ll do little to help those partaking in longer ones. It leaves many with a poor endurance base coming into the critical summer months, and the big question on everyone’s mind is how do we recoup the endurance base we need to be competitive in our target summer events?

Luckily, there’s an easy way to evaluate our current base endurance that doesn’t involve having to suffer the anguish of bonking on our first long training session outdoors, and it’s called cardiac drift.


Cardiac drift works on the premise that a stable heart rate over a period of time at a moderate exercise intensity signifies solid endurance base fitness.

When our heart rate remains constant when compared to power or speed, a parallel relationship known as coupling signifies a healthy base. When the opposite occurs, and heart rate decouples excessively from constant power output, it’s a sign of a lack of aerobic fitness.


There’s a simple way to evaluate your current endurance base, and you can do it in less than an hour on your smart trainer. If you’ve been racing on Zwift or doing the short high-intensity workouts on your smart trainer, then you’ll probably have a fair idea of where your FTP currently lies.

The test involves riding in zone 2 for just under one hour. Zone 2 represents intensities between 55-75% of FTP, and for this test, it’s best to select a power output in the upper half of the zone.

Here’s the protocol:

  • Begin riding at a consistent intensity in upper zone two, keeping your power output constant.
  • After 15 minutes, note your heart rate.
  • Continue riding at the same intensity for a further 30 minutes.
  • Note your heart rate again just before you begin warming down.

What’s of interest is the change in heart rate between both measurements. As a rule of thumb, a change of less than five beats per minute represents a good level of base fitness. Anything between five and ten is borderline, while decoupling of over ten beats per minute is a sign of poor base fitness for zone 2 power output.


Base fitness is more important for certain athletes over others. Athletes competing in relatively short events of an hour or less don’t need to obsess about solid base fitness. But anyone competing in multi-hour events should be alarmed by excessive decoupling.

Ideally, the time in which your heart rate stays within the critical 5 bpm range should correspond to the length of your target event. This means that the longer your event, the longer the coupling needs to be.


If your endurance base needs some work, then there are several ways to improve it, both indoors and out. On the indoor trainer, you can repeat the workout mentioned above, but back off the power intensity. Repeating this one-hour workout two or three times per week and gradually raising the intensity within zone 2 will bring about increases in your endurance base.

Outside, you can ride for longer periods of time. By keeping the intensity within the zone 2 window you’ll target the endurance system. By slowly building towards the length of your target event, increases in base fitness will come about.


While low endurance is commonly associated with heart rate decoupling, this isn’t always the case. Decoupling can also occur due to dehydration or excessive heat, so always minimise the chances of false positives by ensuring proper hydration and environmental control when doing the test.

Regardless of whether you require a solid endurance base or not for your chosen event, it’s always nice to know where you lie. It’s all too easy to get carried away with power numbers in the upper zones. But by taking a holistic approach to our training and targeting each body system as dictated by the nature of our chosen events, we give ourselves the best chance of performing optimally.