Running power has become a term with many definitions. The underlying goal of running power is to create a metrics that runners can train with that is more informative and comprehensive than traditional training metrics like pace and heart rate, but the way that metric is calculated has multiple variations. Stryd is best-in-class for running power, but to understand why first requires a basic understanding of what makes a great training metric.
What Makes A Great Training Metric?
Runners train dynamically. Not every run is done at the same intensity, and not every run is at the intensity of the target race or event. It's well understood that training at a variety of intensities is essential for best performance and proper health as a runner, regardless of the event being trained for. Why? Different training intensities necessitate different physiological responses from one another in runners, and these physiological responses are the basis of athletic improvement. In other words, a great training metric is a proxy for running intensity.
Runners train consistently. It's well-found that athletic performance is improved by consistently stressing the body to prompt specific adaptions that make a runner more fit for the demands they are training for. It's typical for runners to train anywhere from three to 14 times per week. Training sessions are, as just discussed, built around specific intensity goals. This means that a great training metric is not only a proxy for intensity, but is a consistent proxy for intensity day after day.
Running Power IS a Great Training Metric
As explained in the section above, a great training metric is one that is a consistent proxy for intensity of training day after day, in spite of potential varying conditions and terrain. Running power is superior to pace and heart rate training in this regard because of weaknesses to pace and heart rate metrics.
The Problem with Pace: Pace is how fast a runner is moving, but when terrain and environmental conditions change, pace doesn't consistently represent training intensity. Running up a steep hill or into a strong headwind at the same pace is much more intense than the same pace in still conditions or on a descent. This makes it hard to prescribe intensity through pace in varying conditions. Power does not suffer from the same limitations.
The Problem with Heart Rate: The human heart is influenced by countless physiological factors and heart rate varies from day to day in an individual. This is normal, but means that heart rate is a poor proxy for intensity day after day. a low intensity run may have a runner at a heart rate of 140 beats per minute one day and 150 BPM the next day, making it difficult to measure intensity of training over days and weeks.
The Solution is Running Power: Running power is consistently related to the work of training day after day. It will not shift from one day to the next like heart rate. It is a metric which accounts for the changes in intensity due to winds and hills whereas pace will not. For these reasons, running power is a true advancement in training for runners.