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Is Cardiac Drift the Perfect Indoor Training Metric?

Using ERG mode to fix power indoors under controlled conditions, cardiac drift can tell us everything we need to know about how to adjust programming variables (intensity, duration and frequency) based on the state of fitness, fatigue and endurance.

Cardiac drift is a measure of endurance development.

And as a measure of endurance development, it can be used to achieve proper endurance training stimulus by keeping cardiac drift between 5-10%. Below 5%? Increase endurance workout duration. Above 10%? Decrease duration.

And once able to train at target event duration between 5-10%, we (1) have developed adequate endurance, (2) can enter endurance maintenance mode and (3) are ready for higher intensity training.

Cardiac drift can also help substitute intensity for duration. If a 120 minute session is called for but only 90 minutes are available, then simply ride at a power that will elicit a cardiac drift of 5-10%.

Lastly, cardiac drift can also provide insight into fatigue accumulation based on heart rate suppression which disproportionately affects first half average heart rate thereby skewing the measure of cardiac drift upward.

Edit - I forgot to mention that this last point also allows us to more confidently attribute a reduction in average work interval HR to improved fitness as opposed to simply being abnormally lower due to suppression. In other words, lower average work interval HR + same or lower cardiac drift = improved fitness.

Edit #2 - Although implied, it's probably worth specifically pointing out that cardiac drift can be used to adjust intensity (as a tradeoff to duration and in general I'd argue), duration (stimulus) and frequency (fatigue).


  • How did you come to these conclusions?
  • How did you come to these conclusions?

    Mostly an extension of already established concepts made possible by enhanced clarity of insight into status from ERG training due to the purity of the relationship between effort and power which enables changes in performance to more confidently attributed to actual changes in training status.

    Additionally, its reasonable to conclude that, absent of other reasonable/likely explanations, endurance is improving when cardiac drift is decreasing. Directional consistency further supports such conclusions. These phenomenon are also fully reproducible under controlled conditions.

    Heart rate suppression is another known phenomenon with the impact to cardiac drift being simple math.

    The most important variable in any of this is the individual athlete, who is for all practical purposes the subject in an ongoing study with N=1. Focusing on a few, key variables and observing patterns over time is the best way to find the proper limits.

    Fortunately, the application of these concepts is fully compatible with any existing structured training regimen.
  • Problem with use of cardiac drift as a guide is you won't know what level of cardiac drift will occur until deep into a workout (IOW it's too late to be useful as a guide for setting a session's intensity). Besides, the level cardiac drift will be variable day to day for a variety of reasons unrelated to the session's intensity.

    Precisely controlling intensity is unnecessary in any case. What matters is doing enough work at the right levels.
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