Once you start reading any of the several books on training with running and cycling power, you’ll start to get the idea that the question isn’t “should I train by power OR heart rate?” it should be “how I can use power AND heart rate to better understand my training?”

Power is the measure of the work you’re doing, while the change in heart rate is your body’s response to the work. Having to generate more power will cause a higher heart rate and an increase in relative perceived effort (RPE). Pretty simple, right?

One of the main benefits of running with power is the instantaneous feedback on effort. You get real-time change in power, whereas heart rate will lag in response to the change in effort. This lag could be longer than the duration of the training interval, so it’s not the best metric to gauge instantaneous intensity. That being said, running power is extremely useful for hilly terrain and interval training.

Another unique benefit of training with both power and heart rate is the ability to see aerobic decoupling in your post-workout analysis. If your power is staying constant but your heart rate is climbing over time, then you’re fatigued, dehydrated, or something else is going on.

Tracking training stress with a power meter is another huge benefit to your training and racing. Utilizing performance management charts  based on heart rate (TRIMP) and power (Coggan-RSS and Skiba-GOVSS) gives you a lot of insight to your training such as how much you’re improving, your present fitness, and your overall fatigue or training load. Developing your personal power-duration (PD) curve will also give you another tool to allow you to target different efforts for different races. If you have some maximal efforts (training is usually at sub-maximal, so your PD curve will underestimate your critical power and artificially increase other metrics), then your critical power will be estimated fairly accurately, and you can target a known power you can sustain for your race duration.

Unfortunately, running power meters don’t provide a “total view” like most cycling power meters do…it’s really just an estimation of the work you’re doing. There are a few limitations to running power meters that need to be understood so you can better utilize them. For example, they can’t account for additional power output due to wind resistance or a change in ground surface (e.g. asphalt to loose gravel), so you will still need to use perceived effort and heart rate in a lot of cases in concert with running power for a more complete picture. Once you train for long enough with power, you can really get a sense of how hard you’re working. At this point, I can usually guess my power numbers based on feel.

There is plenty of debate on the accuracy of running power meters, too. However, I don’t think it matters how accurate Stryd, Runscribe+, and Garmin’s running power are (yet…), it matters that the values they produce are repeatable and reliable. When you are running at a certain power, you “should” have an RPE associated with that power. Also, when you do intervals or similar workouts, you should be getting similar power numbers. This workout example from a Jack Daniel’s plan shows how repeatable Stryd is. I also have treadmill runs that show that the data produced by Stryd is repeatable. When more running power meters come to market, they should be striving to produce the best data possible.

Running power meters are fairly new, so we have a couple of years before they are held in the same regard as cycling power meters, but that doesn’t mean running power meters aren’t useful.

Run with power: Benefits and why – Coach Ray

Stryd: Running with power – Mark Tallon, PhD

When is running with power superior to running with pace? – TrainingPeaks blog, Hans van Dijk (Co-author of “The Secret of Running”)

The evolution of running with power – Coach Rachel Zambrano

The physics of running power – Ron George blog

Running with a power meter, A clear explanation of the benefits of using a power meter in running – Sporttracks Blog

More to come….