You shouldn’t be running every session the same way: running at different intensities stimulates different energy systems and builds strength, speed, and endurance. (Here are the three essential run workouts all triathletes need to do.)
There are three ways of measuring the intensity of your run sessions: feel, pace, and heart rate. Each method has its own pros and cons that you can use to get the full benefit of your training session as well as fulfill the requirements of your training plan.
You can make use of your innate human ability to feel the intensity of your effort. We use the Rate of Perceived Exertion, or RPE. The traditional Borg scale is a rating from 6 to 20, from “no exertion at all” to “maximal exertion.” However most coaches use a scale from 1 to 10 instead.
Being able to identify where your exertion is on this scale is a useful skill to develop, since it provides you with instant feedback without needing additional tools and helps you make adjustments on the fly whether you need to apply the pressure or ease up a little bit.
The downside of training by feel is that it’s very subjective compared to training with heart rate and pace. Especially if you’re a beginner, you can interpret bodily sensations poorly, with a disconnect between your actual effort and how you perceive the exertion. Without any objective feedback either from devices or people, you can feel really good and fast while running but it’s really just because you’re unknowingly running at a low pace instead. Alternately you might feel you’re just running easy, but your heart rate is already nearing maximum.
Pace is a great way to measure your training intensity in real time. Increasing effort during your runs results in increased pace; there’s no delay in measurement.
The disadvantages of training with pace is that it doesn’t consider how hard you’re working to produce the desired output. There are days you might be putting out more effort to run at the same pace. It also doesn’t take environment into consideration; hillier terrain, higher elevations, and/or cooler or hotter temperatures can impact the effort you put into running at a certain pace. Lastly, attempting to reach faster paces on the monitor feeds your ego, which could increase risk of injury because you might be trying to train above the level you’re currently physically capable of.
When the body is under stress or effort starts to increase, your heart rate increases in response. Training by heart rate is a classic way of checking how much effort and intensity you’re putting into your training session, and is useful for helping you hold back on easy days because you need to keep that heart rate low. Heart rate monitors (whether wrist- or chest-mounted) have made this much easier to do; no need to hold your fingers to your pulse point on the wrist or neck.
One downside of training by heart rate is that its response to a change in effort is delayed. This makes it an unreliable metric during short intense intervals. Temperature, terrain, and elevation can also impact your heart rate. Being dehydrated also makes your heart beat faster, since your blood is thicker which makes it harder for the body to circulate it through your blood vessels.
You also need to make sure your heart rate monitors are properly calibrated, fitted well, and aren’t running low on battery.
Two Metrics in Tandem
Coaches find that measuring effort and intensity using two metrics in tandem is best. Using heart rate alongside RPE will help you learn to identify exertion levels with their respective heart rate and training zones. Pace with heart rate will help you see if you’re pushing too hard even if your pace is telling you otherwise; tracking what pace you run at a certain heart rate over time can also tell you if you’re getting fitter and faster. Linking RPE with pace allows you to dial in the pace and run prescribed sessions even without using a device.
Use these metrics to train smarter, avoid injury or burn out, build your run fitness, and enjoy running even more.