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Heart Rate? Power? Speed? Lactate concentration? Perceived Exertion? Which variables should triatlhletes pay attention to?

Why one number just isn’t enough when it comes to triathlon training

There are a few, basic variables that determine how hard a given workout is going to be. These include the distance or duration of the exercise, the type of exercise and finally, the intensity.  Of all of these, intensity is the one that athletes have the hardest time getting right. This is despite the rise in accessibility and use of GPS-enabled devices, HR monitors, cycling power meters and the like. Athletes regularly go too easy, or even worse, too hard in their workouts, despite their best intentions.

The cause of all of this is that measuring intensity is really hard, even as numerous devices have been invented to make us think that it is easy. It all started with the stopwatch, which is great if you are on the track, or another closed course, but what if you are working out somewhere else? Not only that, but some days a given pace feels harder than it does on others. How do you account for that? Then came portable heart rate (HR) monitors, which purported to solve this problem by giving you a view into what was happening inside the body. Again, limitations were found. Heart rate can be variable on a day-to-day basis and environmental factors such as heat affect it as well. With the advent of power meters, we were told that all of these problems had been solved (at least for sports where you could use a power meter). These devices were objective, don’t depend on terrain or environment and are directly linked to outcomes – if you want to go at X speed, you need to put out Y power, simple as that – right? Power might be more detailed than speed or pace, but again, what are you supposed to do on those days when things just don’t feel right at a given power?

The solution to these problems is to stop trying to rely on just one variable. Instead, you should triangulate the measurement of your effort. One point of your effort triangle should be an objective measurement of your work output. This could be pace, speed or power, depending on what sport you are doing and what equipment you have available. A second point should be an objective measurement of your body’s response to that exercise. The most easily accessed metric for this is HR, but blood lactate concentration is another example of a variable you could track for this. The final measurement that you should track is a subjective measurement of your relative workload. What do I mean by this? Simply put, it is a self-assessment of how hard you feel you are working. It is often codified as a “rating of perceived exertion” or RPE and is commonly measured on a scale of 1-10 with 1 representing “resting on the couch” and 10 representing “working as hard as absolutely possible.” Despite the apparent simplicity, this tool has shown to be a remarkably useful way to monitor exercise intensity. It turns out that people are pretty good at knowing how hard they are working!

Once you are tracking three points of intensity, you can make more nuanced assessments of your effort. For example, if you are supposed to be doing a steady, easy run and find that your RPE and pace are in the right zone, but your HR is higher than it should be, it might key you in to pay more attention to other details to make sure that you don’t overload your body beyond what is intended for the workout.  Maybe it is extra hot and you need to temper your pace to keep your HR from creeping up even further, or maybe you had an extra coffee that morning and the higher-than-normal HR isn’t a big deal. In either of those situations, the extra information from the additional data points allows you to be more nuanced in calibrating your effort, as compared to how you might be able to respond if you were only tracking pace, or only tracking HR.

Overall, it is important to recognize that just tracking one number only gives a partial picture of what is going on in your training.  Using three metrics to take in the larger view can catch help identify some of the reasons why you may be not be getting the most out of your training and can keep you on track towards your goals!

Darian Silk is a triathlon coach and Clinical Exercise Physiologist based in Toronto.  Read more about Darian here or email him at darian@teamatomica.com.  You can also check out his TrainingPeaks profile here.