Using power to guide your running: Why and how

Dr Breanne Kunstler (BBiomedSci, BHealthSci, MPhysio, PhD).

Physiotherapist, behaviour change scientist and run coach.

What is “running power”?

Let’s start with an analogy: 

You are walking in the park and feel water beginning to drop lightly on your shoulders. That’s OK, a little rain never hurt anyone and it’s certainly not going to stop you going for a walk in your favourite park on such a beautiful, sunny day. Wait…sunny? Yes, it’s a warm, sunny day. The temperature and the absence of clouds in the sky, together with your choice of summer outfit and knowledge that today is meant to be sunny, conflict with the feeling of raindrops on your shoulders. Ah, it rained last night! Those drops must just be left over rain falling from the leaves of the trees above you.

The above example shows that, when coming to a conclusion, we can use one piece of information (feeling of rain drops = raining) or many pieces of information (sunny and warm day ≠ raining). Often, the more information we have, the more accurate the conclusion. 

Using power when you run gives you many pieces of information to come to a more accurate conclusion. Power tells you the amount of work you are doing when you run, or how hard your body is working based on many different pieces of information.

Why should I use running power?

Cyclists have used power for much longer than runners have. They do this because it’s a good way for them to know how hard they are riding during their current ride compared to previous rides that may have been done in different weather conditions, over different elevation and when their body was in peak (or depleted) condition. It’s hard to compare how much work, or effort, you have put in over different rides with so many variables at play unless you measure power. Power considers the many pieces of information collected during a ride to give cyclists a ‘one stop shop’ of how hard they have worked. Now it’s runners’ turn to utilise this data powerhouse!

“But doesn’t heart rate and pace tell me how hard I am working?” I hear you say. To an extent, yes, heart rate can tell you how hard you are working. Your heart beating faster during exercise usually suggests that your body is working harder than at rest. However, using just one variable, like heart rate, is like using water drops on your shoulders to tell you that it’s raining. It can be misleading when used by itself.

Running power takes into account many different data types to give you a better picture of how hard you are working during, and between, runs. For example, running at a slow pace can either indicate that you are just cruising on the flat or running up an extremely steep hill. One effort is easy, one is hard. So, looking at pace alone is misleading when it comes to estimating how hard you are working. 

Have a look at Image 1 below. This is from one of my runs. I have marked where I was running at a pace almost 50 seconds per kilometer slower than my fastest pace that day and my power was at it's highest. So, if I went just on my pace, I'd think that I was just cruising at that point of my run. In fact, I was working really hard. For the record, my heart rate was high at that point too, but it certainly wasn't the highest. Therefore, using pace and even heart rate by itself doesn't give you the most accurate picture of how hard you are working.

Image 1: You can still be working really hard (high power) at a slower pace and moderate heart rate

What if you could link information about pace and heart rate in with elevation, weather conditions, ground contact time, vertical oscillation, stride length, step rate etc. to get an overall measure of how hard you are working? As a coach, I love this idea, because I often have clients tell me how disappointed they are when they didn’t reach the pace they wanted to during an important training run or event. They want to know why the run was so terrible. Knowing how hard their body was working during each run (i.e. looking at their power rating alongside other data [Image 2]) compared to others allows me to explain to runners why some runs feel harder than others. This then allows me to provide them with specific advice on how to get the best from their body going forward.

Image 2: The amount of information you get from an activity tracker can be overwhelming (but so useful!)

What devices do I need to measure running power?

Regular runners can measure power with some simple equipment. However, don’t expect the data to be as accurate as what you might get in a biomechanics lab.

Knowing what device you need depends on what technology you run with. You will need to embrace technology to measure power. However, this doesn’t mean that you need to start carrying heaps of stuff. I have a Garmin Fenix 6s watch that is compatible with a Garmin Running Dynamics Pod. So I run with my regular watch and a little device that clips onto the back of my tights. The pod is so tiny! I’m so worried that it’s going to fall off! However, upon trying it several times, it seems to sit steady. I’m also a little concerned that my toddler will eat it. So, make sure to keep it away from little humans and animals. You can also try a chest strap if you don’t like the idea of the pod. I personally don’t like wearing a chest strap so the pod was a better option for me.

Who should run with power?

It is not necessary for everyone to run with power. However, I recommend those who are training hard to improve their speed or distance for a certain event, or competitive recreational and professional athletes, to give it a go. You might find that it becomes much easier to know how hard you are working during a run, which is important because you’ll see if you are working harder than usual and be able to decide whether or not you need to pull back to make sure you avoid overtraining or bonking during key training runs and events. 

Monitoring power can help you to see if you are at risk of burnout or excessive training. Seeing your power over consecutive runs, and therefore how hard you have been working over time, gives you an idea of whether you need to introduce more recovery time (i.e. your power is reducing over time and you are feeling exhausted) to continue running injury free. Effective and regular recovery is necessary to prevent injury and make sure you achieve your goals. As Prof Shona Halson says, "The only training you benefit from is the training you recovery from" and she knows her stuff.

In summary

Running power gives you a good idea of how hard your run was, or the load it placed on your body, because it uses heaps of different pieces of information to give you one number. Having one number makes it easier for runners to compare different runs and know what runs were truly hard and which ones were comparatively easy. Runners can also monitor their power within a run, allowing them to decide how hard they want to work at different stages of a run (i.e. working within certain power ‘zones’, like heart rate zones), allowing them to save energy early in the race to use it at the finish line. Importantly, having all this information gives runners better information around how much recovery they need before running again, as they have a much better idea of exactly how hard they thrashed their body during their recent effort/s. 

So, running with power is a step up in the use of technology and effort you put into analysing your runs, but if you have big goals or simply want to make sure you are recovering well, then give power a go!

Run well, my fellow humans.