The Emerging Technology of Running Power

It isn’t perfect, but running power solves some of the most common problems runners face in training.

It wasn’t very long ago that training for running was a trial-and-error affair. Runners experimented with everything from high intensity track workouts every day to 200+ miles a week at paces that veered towards walking.

Today the sport looks very different. The variation in approach has all but vanished, and the practices of the greats like Arthur Lydiard have become immortalized as the only way to train for peak endurance performance. Around 80% of an athlete’s training time should be spent at low intensity, with the remaining 20% being a split of moderate and high intensity.

But what indicators separate low intensity from moderate, and moderate from high? Runners have historically built a training structure using common running metrics like pace, heart rate, and perceived effort (RPE). The problem as it turns out, is that each has its own limitations making it an unreliable gauge of intensity at one time or another. More recently there has been increased chatter about a new training metric making its way into running watches, footpods, and chest straps called running power. It’s a new take on the conventional 5-zone training system and a little bit confusing, but could it mean the guesswork of training intensity is behind us?

What is running power?

Running power tends to be a confusing concept because, in some ways, it’s less intuitive than the industry standard metrics of pace, heart rate, and RPE. At the same time, it is also more natural in some ways. Any runner can tell you that running up a hill is harder than across a flat at the same speed. The same goes for running into a stiff headwind compared to running on a still afternoon. Running power is the quantification of that added (or reduced) resistance.

But what does the term “running power” mean? The shortest version is that it is a calculated estimate of a runner’s running metabolism. The unseeable chemical process occurring in the body as oxygen, fats, and carbohydrates come together to create ATP, the molecular fuel that our working muscles use to move our bodies. In truth, all of the metrics commonly used by runners in the 5-zone intensity system are trying to achieve this same goal of finding a reliable proxy for our rate of energy use. And in reality, what we’re calling “running power” requires laboratory equipment to precisely measure, but recent advancements in biomechanics research and motion-capture technology have added viability to some estimates.

In heart rate training we use beats per minute, in pace we use minutes per mile or kilometer, and in running power, we use watts.

The argument for running power

Full disclosure: I work for a company that specializes in running power and has developed what’s widely accepted as the gold standard. The argument for using running power as a key training metric assumes that you are using a quality running power meter, which are starting to become more readily available from sports technology brands.

The argument for running power alleges that power accounts for the pitfalls that plague pace, heart rate, and RPE. So what are those pitfalls and how is power different?

Runners using a pace target can experience wild fluctuation in energy output when they encounter hills and headwinds, even if they abide by their target. Depending on how drastic the change in these conditions are, it could mean a difference as significant as that between sprint intensity and walking intensity, thus defeating the purpose of even having “zones” to aim for. Power meters give visibility into the changing demand so a runner can compensate for those environmental factors.

Runners utilizing a heart rate (HR) goal are able to modulate intensity a bit better because the heart rate almost always reflects a change in demand; but there are two caveats. First, HR can be delayed by seconds to minutes in reflecting that change, which could be long enough to leave a runner flying blind in an interval workout with short efforts or recoveries. The next workout segment often begins before HR adjusts to reflect the energy demand of the last segment (i.e. hill workouts, strides, and others). The second is that HR values can be different from one day to the next due to dehydration, work day stress and other factors not related to running, which makes it hard to compare the data of similar workouts. By contrast, the relation of a power target to running intensity is much less likely to change from day to day, and power meters are able to respond to changes in output almost instantly.

RPE passes physical intensity through the mind of the runner and thus adds another factor that can influence, modify, or even taint the resulting output: psychology.

Running “on feel” can be beneficial if the determination is made objectively and consistently from day to day, but that requires the runner to know how the session should feel, to omit thoughts or emotions that could inject bias, and to stay free of distractions throughout the workout. Avoiding all three roadblocks consistently from day to day and month to month is nearly impossible and can often lead to very unpredictable results. There are two variables clouding each other- physical demand and the mind’s perception of that demand. A power target is not subjective in this way. Watts are a physical measure and their value can’t be warped by perception.

In short, the argument for running power is that it’s more encompassing than pace, more responsive and consistent than heart rate, and is an objective measure not influenced by human psychology like RPE.

New blindspots

While running power solves the problems presented by more common metrics, it has its own gaps in considerations.

Muscle Fatigue

With all this concern about metabolic demand, it’s easy to forget the importance of individual muscles on metabolic output. But in the end, it’s up to the legs to transfer all that metabolic energy to the ground.

Muscles weaken as the small fibers they’re composed of break down under the prolonged strain of running, just as muscles weaken when you lift a heavy weight for a few reps in a strength session. All the metabolic energy in the world won’t repair a tired and broken muscle halfway through a marathon. Without the integrity of the muscles in your legs, there is no way to get metabolic energy from the body to the ground. The distinction becomes most obvious in downhill running or steep uphill where the muscle recruitment shifts to fewer muscles that are placed under greater strain with every step. In a steep downhill, for example, power and heart rate sag while maintaining a constant pace, but you’re still likely to notice the extra pounding on your quads. Running power meters today are ill-equipped to understand limitations enforced by the muscular component of intensity.

Focus

The benefit of power is that it accounts for running-related energy and nothing else. It will capture speed, elevation gain, and wind, but eliminates non-running variables that might affect heart rate. In order to work, running power presupposes that the metabolics for running will not change in response to dehydration and mental stress.

Even though dehydration and workday stress don’t make you a faster runner, like it or not, they do still impact your training. Is it best to breathe a little harder to hit your normal easy-day power targets, or to back off because it feels much harder to hit that target today? Most running coaches will tell you to listen to your body when something seems off.

Altitude

Most of us train at the same altitude on most days, perhaps with exception to those in mountainous regions. Still, today’s running power meters are unequipped to compensate for the metabolic changes that occur if you’re used to training at sea level and suddenly travel to 10,000 ft. for a week of altitude training. The body’s capacity to metabolize fuels at altitude can be drastically cut due to the reduced oxygen availability, and a runner’s power zones will have to change. Imperfect as they are, RPE and heart rate will win out over power and pace in these conditions because the in-run values automatically reflect (at least to some extent) the effects of altitude on aerobic energy production.

Conclusion

Where does all of this leave the fate of running power? In order to reliably put 80/20 training concepts into practice by balancing low, moderate and high intensity training, athletes need an intensity measure that’s responsive, consistent, comprehensive, and objective. It could be argued that running power, while imperfect, earns a higher aggregate score among these requirements than more traditional metrics.

As an athlete and a coach I’ve never believed that training should be completely unilateral. There’s no single metric used today that will capture the whole athlete, but objective measures are a valuable complement to the subjective thoughts of an athlete. They allow us to not only look at each data point in isolation, but also to draw connections that can provide greater insight. Power is a tech-heavy way of collecting objective running data but, in the right conditions, maybe better.

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