Working on endurance: with a power meter or with a heart rate monitor?

Following up on our article about the benefits of low-intensity training for progress, here are some tips for managing this type of ride if you’re equipped with a heart rate monitor or power meter.

By Guillaume Judas – Photos: depositphotos.com

Contrary to many preconceived notions, simply pedaling like crazy without thinking is not enough to make progress, especially in the long term. To build a solid physical condition and see profound metabolic changes, and then be able to put in the necessary effort to gain power, you need to dedicate a lot of time to what is called low-intensity training, or “endurance” training.

But be careful, true endurance training does not consist of accumulating hours in the saddle at a slow pace. Of course, “old-school” rides with a few companions of the same level, covering km and gradually increasing mileage each week, produce good results. This is provided that you share the workload, avoid staying hidden in the wheels for three-quarters of the ride, and also avoid overly frequent race simulations.

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True endurance training is done at a target pace, and maximizing time spent in the target zone optimizes the training. In other words, a well-executed 3-hour ride is more beneficial than a 5-hour ride done imprecisely, alternating between moments of too little effort and others in race mode. For endurance, we’re talking about an intensity that corresponds to an effort without any muscle pain, allowing for easy conversation, leading to normal fatigue after 3 or 4 hours, and in an effort zone between 50 to 65% of MAP and 75 to 85% of Max HR. So that means: easy, but “busy,” or “focused.”

For a cyclist with a MAP (Maximum Aerobic Power) of 360 watts and a Max HR (Maximum Heart Rate) of 170 beats per minute, the target pace for endurance training is therefore 180 to 230 watts, and approximately 125 to 145 beats per minute. For a cyclist with a MAP of 300 watts and a Max HR of 200 beats per minute, values between 150 and 195 watts for power, and between 150 and 170 beats per minute for heart rate should be targeted. This is why this type of session must be individualized or carried out in a small group with cyclists of an equivalent level. Otherwise, the weaker cyclist risks not working in the right zone and therefore not doing productive work, and the stronger cyclist risks wasting their time. Hiding in the wheels behind stronger riders is also not an excellent solution, because the energy savings achieved on the flats are too high for the session to be profitable, and conversely, there is always a risk of going into the red on climbs when following better-trained cyclists.

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Heart rate monitor or power meter to accurately target the desired intensity?

When MAP and Max HR are known, it is quite easy to determine the target training zone, at least theoretically. However, it should be noted that power is a direct measure of the effort provided, whereas heart rate is an indirect measure. For a very short and very intense sprint, for example, with maximum power over a short distance, heart rate is not significant. The heart does not have time to “climb.” Conversely, on a small descent or when passing a roundabout, there is little or no power production, yet the heart takes some time to “descend” to a value close to rest. And this phenomenon is all the more noticeable as fatigue sets in during a session. On the other hand, the more physical condition improves, the faster the heart rate drops after exertion. This is called cardiac braking.

Ideally, an endurance ride is productive when the power and heart rate curves follow the same trend, and it is possible to maintain the same power without seeing the heart rate curve drift upwards, or conversely, without seeing the power curve drop while maintaining the same heart rate values. If this is the case, it means that the session is poorly conducted, or that the athlete is reaching the limits of fatigue relative to their current physical condition.

Both tools are therefore useful for successfully completing an endurance session. Nevertheless, a heart rate monitor can be considered sufficient during the winter period, or at least when resuming regular activity. This is because Max HR is little impacted by the training level, unlike power and MAP and FTP (Functional Threshold Power, or the maximum power a cyclist can sustain for 1 hour) values. Ventilatory thresholds linked to heart rate are also not very dependent on physical condition. Thus, relying on the 75-85% Max HR range during a training resumption period helps avoid major errors. On flat or gently rolling courses with few accelerations, consistently staying in this target zone while very gradually increasing the duration of sessions already allows for significant progress, even before imposing a painful MAP or FTP test.

Because in the case of power training, respecting the correct target zone requires knowing your MAP (or FTP) in order to deduce the correct intensity values to adhere to. Power production drops quite quickly after a period of detraining, and it naturally takes several sessions to regain previous values, which are linked to both physical condition and technical pedaling mastery. MAP is therefore not a fixed value throughout the year, and it can easily vary by 20 to 30% for the same individual between peak form and complete detraining. With a power meter installed on the bike, it is possible to regularly test your MAP to update it by making a maximal effort for 5 minutes. But this remains a very demanding effort, and not very reliable when resuming training.

When the condition is more solid and MAP and FTP values are approaching their best level (or at least starting to be stable compared to what is observed on the road), the power meter becomes a more reliable tool for effective endurance training, without taking into account the inertia of heart rate. With a power meter, it thus becomes possible to smooth out the effort as much as possible to spend the maximum amount of time within the desired zone. But pedaling continuously within a 40 to 50 watt range is not as easy as it sounds. This implies avoiding power spikes in response to the terrain (small hills, false flats, accelerations…) but also maintaining constant pressure on the pedals on descents and false flats, and limiting all coasting moments.

Indoor trainer for endurance?

Thanks to new devices and applications, indoor trainer practice is no longer as tedious as it was a few years ago, both in terms of sensations and fun. Provided you train in a cool, well-ventilated room, it becomes possible to do fairly long sessions on varied virtual courses, whether to compensate for capricious weather or to train during the week despite the early nightfall.

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The indoor trainer offers the advantage of allowing you to ride while controlling a maximum of parameters, which is ideally suited for endurance work. By avoiding all the risks associated with traffic, and all situations likely to interrupt pedaling, indoor trainer practice allows you to pedal very regularly in the target zone, whether in power or heart rate. And since there is no coasting time, the time spent pedaling is truly optimized for training at the desired intensity. There’s no need to string together long sessions to work on endurance. In addition to a single long ride per week, several shorter rides contribute to progress as long as the effort zones are respected.

However, it is necessary to take the same precautions as for road training: heart rate is likely to drift with fatigue, especially if dehydration related to indoor conditions is added. As for power training on an indoor trainer, it is essential to opt for specific benchmarks, because power on the road is not necessarily the same as on the indoor trainer, as it depends on the type of device, the software, or even the way one pedals on the road and indoors.

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