Changes

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.

So far, only RunScribe has been transparent about the model they use for running power, which is available as an online calculator at [https://runscribe.com/power/RunScribe.com]. Your power output is going to be closely related to your [[Running Economy]], and there's quite a bit known about [[The Science of Running Economy]]. The three most important inputs to the model are:

Below is a graph from the book "The Secret Of Running", which compares power output and V̇O_2. It's claiming that this shows "the stride data I just as good as the V̇O₂." However, this only shows that the [[Stryd]] estimate of power varies linearly with pace, which given pace is a primary input to power estimate should come as no surprise. It also shows that oxygen consumption is also linear with pace, something that is well known. However, the power estimate for a given oxygen consumption varies dramatically. You can see for 40 ml/Kg/min, the estimate varies from 2.5 w/Kg to 4.0 w/Kg, a nearly 40% variation. See [https://hetgeheimvanhardlopen.nl/wp-content/uploads/2016/11/3-The-running-economy-of-14-test-runners.pdf hetgeheimvanhardlopen.nl] for more details.[[File:StrydVo2.png|center|thumb|300px|Data from "The Secret Of Running" book.]]Stryd have released their own evaluation at [https://storage.googleapis.com/stryd_static_assets/stryd-metric-validation.pdf Stryd Metric Validation]. Their data shows "Stryd power is 96% correlated with metabolic energy expenditure", but the study was on 13 runners and the correlation is only a subset of 9 of them.[[File:StrydVO2-2.jpg|center|thumb|300px|Data from an evaluation performed by [[Stryd]].]]