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Running power meters estimate running power by modeling a runner using inputs such as pace and incline (see below for details.) This means that they are only a rough estimate, unlike cycling power meters that actually measure power directly (again, see below for details.) There's an old saying that "[[All models are wrong]]| all models are wrong, but some models are useful." So, while running power meters can't measure your power output, they can still be useful. It's possible for a running power meter to estimate how an incline or decline changes exercise intensity for a given pace. This can allow for more even pacing on hilly courses, which gives a more even effort when training. More importantly, it can allow for more even pacing on a hilly race, which would be great for things like the Boston Marathon. This could be more effective than [[Heart Rate]], which suffers from a significant lag between changes in intensity and a change in Heart Rate, as well as [[Heart Rate Drift]]. A running power meter can also be useful when doing uphill interval training, where they can provide some insight into the effort required compared with level ground.=Power Estimate or Heart Rate?=The use of heart rate for training has been established for many years, and heart rate based training has some useful advantages, as well as some significant shortcomings. I think the estimate of power output overcome some, but not all of the issues with heart rate based training. Personally, I don't see this type of power estimate completely replacing heart rate based training, only augmenting it. * Heart rate responds to exercise intensity with a delay, while power estimate is much closer to real-time. * During longer exercise, [[Heart Rate Drift]] occurs that generally causes a higher heart rate for a given intensity. The reasons for this drift are complex, and include dehydration, fatigue, carbohydrate depletion. Using a power estimate ignores this drift, though it's unclear to me when to use heart rate and when to use the power estimate. In some situations, it seems likely that the drifted heart rate is a better estimate of intensity than an unmodified power estimate. * There is a widespread myth that [[Maximum Heart Rate]] can be calculated, leading to some erroneous assumptions of how a given heart rate relates to the percentage of exercise capacity. In practice, both Heart Rate and maximum estimated power require a practical test.* A common use of heart rate data is to allow an athlete to train at their [[Lactate Threshold]], often referred to as [[Tempo Runs]]. The belief is that this training intensity is especially beneficial, though the available science indicates the opposite. If Tempo Runs made sense, then a power estimate would be quite valuable for hitting that pace accurately. I'm sure that many runners will use power estimates this way, even though the science indicates it is ineffective.
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[[File:RunningPowerMeters.jpg|right|thumb|200px|Two [[Running Sensors]] that estimate running power, the [[Stryd]] on the left and [[SHFT]] on the right.]]
I've tested many of the running power meters that are currently on the market. While some of them are remarkably useless, some of them can provide value as long as you understand the limitations.
=Limitations of Running Power Meters=
Here are the primary limitations of running power meters, and different sections of this article will go into more detail on some of them.
* They are not "power meters" in the sense of actually measuring power. Running power meters estimate running power by modeling a runner using inputs such as pace and incline (see below for details.) This means that they are only a rough estimate, unlike cycling power meters that actually measure power directly (again, see below for details.)
* A key input to any running power estimate is your speed. That means they are dependent on whatever mechanism they using for measuring your running pace. Any system that relies on GPS for pace will be deeply flawed under many circumstances.
* The second major input to a running power estimate is incline or decline, and modern pressure sensors can give a good estimate of slope. However, they don't tend to work well for slight angles, and most systems seem to include a fair bit of smoothing, so the response to elevation changes is slower than a Footpod can detect pace changes. This can produce some art artifacts when you run up a short steep slope for instance. Often, the power estimate will detect you slowed up, and drop your power estimate quite low, then when you're back on relatively level ground it will notice the incline change and combine it with your level running pace, producing a really high estimate of power.
* Because they are not measuring power, they provide no useful insight into [[Running Economy]]. This seems to be a common misunderstanding.
=Are They Useful?=
=Running Power Meters Tested=
I've tested a number of running power meters, and they vary vastly in the usefulness.