Home Cycling Tips 7: from heart rate to power analysis

You may have recently seen a strange cycle-computer on some bikes that looks bigger than usual: it is probably the reader of a power sensor. The power reader is just the latest product of the technology on board the bike.

In general, the heart rate is perfect for tests performed in the laboratory, where it shows a perfect correlation with the increase in external load (power produced). It is less perfect in testing for road practice, where it suffers from a series of limitations, consisting precisely of its response that is a little slow but also susceptibility to fatigue, altitude, coffee consumption and the time of day.

In this article, we will discover in detail the advantages and disadvantages of using heart rate as a parameter to analyse cycling performance.

From the cycle computer to the heart rate monitor

The cycle computer was a tool that became common since the 80's and allowed millions of cyclists to train in a more scientific way knowing some basic data: speed, distance and, later, the cadence. The first cycle computers that showed the parameters of speed and cadence allowed a great step forward in the management of training, but some variables such as air resistance and altimetry did not allow training sessions to be compared effectively, especially if performed on different routes.

Then came the heart rate monitors, which have revolutionised the training of the cyclist since, about twenty years ago, have become common and easy to access. With these tools, the cyclist began to measure the so-called internal load, the heart rate, and to adjust the training according to the target heart rate that you wanted to maintain.

Heart rate: where it doesn't work

Expressions such as threshold rate, training heart rate, anaerobic threshold rate etc. have become part of the cycling jargon. Although it is a very valid parameter for the cyclist's training and irreplaceable in the testing phases, the heart rate has some limits.

Firstly, heart rate has a slow response to changing workloads and it is often difficult to perform exercises based on point values (e.g. 140 beats per minute), especially when the terrain is very undulating and repeated.

Secondly, in the case of short repeats or sprints, the heart rate response is usually not instantaneous in the case of short repeats or sprints, although this goes up with increasing effort. For example, if a 10" sprint was performed, the heart would not rise suddenly; for example, starting from 130 beats per minute, after the shot it would reach 140, and this value would continue to grow even after the effort, and then drop very slowly.

It is clear, therefore, that in this case one could not rely on the heart rate to regulate the intensity of the effort.

Finally, heart rate analysis can be misleading in the case of retrospective analysis of a workout. For example, if you analyse heart rate graphs from a purely quantitative point of view (such as average values) without knowing further details, you may come to the wrong conclusions.

A session consisting of intense neuromuscular efforts, made by a series of short sprints, could in fact be mistaken for a slow background training, because for most of the time the work would seem to be done at low to medium heart rate despite having performed a series of intense efforts.

Heart rate: where and how it works

On the other hand, the heart rate is therefore ideal for monitoring prolonged and constant efforts, but even in this case you need to know how to use the tool and know each other well to dose the energy.

If, for example, at the beginning of training you wanted to immediately reach the zone of medium-high intensity (corresponding, for example, in the case of a certain subject to 150 beats), you would start the training by pushing too hard and finding yourself pedalling at an intensity higher than needed, because the heart needs time to increase its frequency. In addition, the heart rate has daily variations that depend on the stages of shape or fatigue.

The arrival of power sensors

The heart is a muscle like any other, and when it is tired it usually slows down its performance; at other times it runs faster.

Ultimately, the heart rate is therefore influenced by so many factors that many athletes, when they train or when they compete, prefer not to know it, because it could be misleading, and focus on the perceived effort.

On a given day, for example, 120 beats per minute allow you to pedal at 25 km/h, while on another day to pedal at the same speed your heart could rise to 130 beats.

Recently, power sensors have arrived, which are the most reliable and objective system to measure performance and control the training of the cyclist that we will learn more about in another article to follow shortly.