Power vs. Heart Rate

A lot of athletes question whether they should train with power or heart rate, and which one is the "best". It is not such a straightforward question to answer. Both metrics give valuable information and have their own pros and cons. Heart rate is a good, cost effective way to measure intensity but is not as accurate as training with power and more susceptible to external factors. Power is very accurate but can be a costly investment and is still relative to the athlete's physical and, to some extent, their mental condition. In this blog we will delve a little more into each metric and hopefully give you some useful information to consider for adopting into your training regimes.


Heart Rate

Training with heart rate has long been a staple part of endurance training and for most is still the most cost effective, important metric to use. The biggest hurdle to consider when training with heart rate however, is that there are many variables to consider and understand to ensure you can use it effectively.


The biggest issue in utilising heart rate during training is to understand cardiac drift. A great article is available on the Polar blog where a great definition is given:


Cardiac drift can be defined as the upward drift of heart rate over time, coupled with a progressive decline in stroke volume and the continued maintenance of cardiac output. Cardiac drift occurs while exercise intensity remains constant.


The below screen grab shows cardiac drift visually when recently evaluating an athlete's training session. Whilst the power output stays relatively contstant over the high power output it is clear to see the cardiac drift extend over half a minute after the effort was completed. Another factor to take into consideration when looking at training data, in particular for this specific session, is the environment. This session was conducted indoors where athletes are more prone to higher body temperature. Various studies have been undertaken that suggest less drift occurs when training outdoors where the wind helps to cool the body temperature.

Always remember the most important aspect is to ensure a proper heart rate threshold is set in order to truly determine if their is a cardiac drift occuring and to what extent. If your threshold is set too low then you will experience a larger range of drift. Check out this link on how to set Heart Rate Zones?


Power

Power meters have really taken off in use of the non professional athlete in the last 10-15 years. Power meters provide a precise measurement of effort and allows the ability to view strength of one athlete compared to another by using a metric called watts per kilogram (w/Kg). The screengrab below gives a great visual demonstration of how using power for pacing can be a much stronger means for training and racing compared to heart rate which can be seen to fluctuate as the power remains constant.

The biggest downside of training with power is the cost. Whilst the cost has dropped significantly over the last decade it will set you back a few hundreds pound for a basic, single sided power meter compared to as little as £30-£40 for a good heart rate monitor.


So what's best?

The easiest answer....using both metrics together. However, as we have looked at they both have their pros and cons. For a coach working with athletes having the ability to view both metrics together introduces another...you guessed it....metric! Aerobic Decoupling is the ratio between Power and Heart Rate (Pw:HR). There will always be a disconnect between heart rate and power as one metric remains steady and the other drifts higher or lower. That disconnect is referred to as Aerobic Decoupling and is a great indicator on the current aerobic endurance fitness of the athlete. Excessive amounts of decoupling indicates a lack of aerobic endurance fitness so the lower the ratio the less decoupling you are expericing. There is a great article if you want read more over on the TrainingPeaks blog.

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