Anyone training with running power? If so, according to DC Rainmaker (provided I am understanding him correctly), the devices don’t seem to notice a difference between surfaces and seems to record power the same at any given pace no matter what the surface…
The question is is there a noticeable amount of wattage error (either by % or by the actual number of watts) across surfaces? For example, if 300 watts got you a 7:30 pace at 150 lb weight, 3% gradient on a road, then according to the device, that same pace on the same gradient (assuming you are the same weight) will get you the same amount of power on a trail, which of course can’t be 100% accurate. In this case the question would be how many watts is it off by?
Answers could be something like 10 watts on a light trail, 15 watts on soft trail, 20 watts grass, 30 watts sand (or percentages %%). I’d be curious. Also, if none of the ‘running power’ devices out there are doing this, it couldn’t hurt to allow the user to input this data. Somehow I think this might help them understand the variances…idk…
Also, don’t use these numbers above for anything as I can be way off since I haven’t used power running yet… I am asking because I might add the chest strap and it pairs with the Garmin I have so I will likely become curious to what I am seeing.
interesting question, a lot of variables in trail running…
i’d pose a similar question but with less variables - how well do running power devices reflect the pace/effort differences between shoes?
None of the running power meters can see inefficiency differences from running surface or shoes. In super-simple terms, all they do is multiply your weight times your velocity times a constant of their making.
They are fun and useful for managing interval training and race efforts. But you will need to know your numbers on the surfaces you run. If you normally run on asphalt your power numbers will be meaningless on a trail run. But, if you train on trails, then those power numbers will be helpful on a trail race.
That’s exactly my point - what’s the average difference most people see between one surface medium and the other at any given effort… Is 300 on the road going to be like 280 on the trail (because you are really running 300, but the calculation isn’t picking it up because you are moving slower…)…
Essentially, for those who use them, what differences are they seeing and which device are they using that they see it with… This could make this more quantifiable.
None of the running power meters can see inefficiency differences from running surface or shoes. In super-simple terms, all they do is multiply your weight times your velocity times a constant of their making.
They are fun and useful for managing interval training and race efforts. But you will need to know your numbers on the surfaces you run. If you normally run on asphalt your power numbers will be meaningless on a trail run. But, if you train on trails, then those power numbers will be helpful on a trail race.
Runscribe provides a lot more than a mere power constant. Arguably its best output is its “shoe prints†and various other “‘metrics,†which can and do vary between running styles and shoes. I purchased Runscribe Red with sacral sensor. I credit the data it provided with helping me figure out why I had tight shins on some runs and certain shoes.
None of the running power meters can see inefficiency differences from running surface or shoes. In super-simple terms, all they do is multiply your weight times your velocity times a constant of their making.
I don’t think the calculation method you describe is true. The run power measuring devices that I have used detect differences in stride and differences in gradient. The use accelerometers to analyse stride rather than simple pace. Most will include ground contact time and vertical oscillation in their calculations too.
I do think your comment about running surface and shoe differences is true. Stryd has announced an update today that allow you to assign “profiles†to a run for the running surface where they use a different calculation depending on the surface (which would confirm that they can’t detect it reasonably).
Edited to more clearly identify which bit I thought was different to the earlier post.
I don’t think the calculation method you describe is true. The run power measuring devices that I have used detect differences in stride and differences in gradient. The use accelerometers to analyse stride rather than simple pace. Most will include ground contact time and vertical oscillation in their calculations too.I used “super-simple terms” for the illustration, but yeah, it is true.
Yes, the good ones have multi-dimensional accelerometers that trace the foot through 3D space. And yes they are factoring vertical oscillation in the calculations. But all those wash out with the dominant part of the physics equation which is how much weight moved down the road how fast. It distills to weight, distance, time and efficiency factor.
I am running with three different running PMs now and I am comparing power numbers to friends running with them the same time as me. The results are highly consistent between them, which is what I would expect with a simple mathematical equation. Garmin uses an efficiency constant 35% bigger than Stryd. Apple uses an efficiency constant 2% lower than Stryd. This is almost perfectly consistent up & down hills and during intervals of all different paces. With others running with me, their power is directly proportional to our weight differences. In other words, mass times velocity times efficiency constant.
Another cool viewpoint… When you divide average watts by speed in meters/second, you get average newtons. This is the average force the device thinks I am exerting. That number does not vary by more than 1% on closed-loop courses for any of the devices in hundreds of miles of running. In other words force (average newtons) is just mass times their efficiency constant.
what’s the average difference most people see between one surface medium and the other at any given effort…Sorry for my non-answer answer. The point I want to highlight is that power error as a function of running surface is entirely an individual, subjective perception. And, it does not require someone with a running power meter to answer the question.
So, if you answered it for yourself - when you run on asphalt versus a trail, what % slower is your trail pace at the same level of perceived effort? This would translate to your power “error.” Same with anyone else who answered - it would be for a given RPE, what percent difference is pace or power on trail versus road. It does not matter if they answer for pace or power, because the two are directly proportional with a running power meter.
That is very interesting. I have only regularly used two devices and gradient is a huge factor for me contrary to what you and your friends have seen. My running gait at some speeds also can be noticeable (albeit not terribly actionable because my most “natural†gait is invariably the best one).
I am sure there will be reasons for the different experience and it may be that I am not a particularly “natural†runner and perhaps these other factors only kick in so much with lower efficiency values.
I have only regularly used two devices and gradient is a huge factor for me contrary to what you and your friends have seen. Yes, gradient is a factor, and all the devices handle that the same. (Well, I think that Stryd and Apple probably handle gradient better than Garmin.) I did not focus on gradient, because it is not a differentiator between them, and it distracts from the simplicity of the physics calculation.
The impact of gradient jumps out in the calculation of avg newtons in the splits. I used a fairly steep 1/2 mile uphill to test, and my avg newtons for that split jump up about 36% with Garmin (30% with Stryd) and drop 19% and 16% (Garmin vs. Stryd) going down the exact same hill.
So really, the math is weight times speed times efficiency constant times gradient factor (and times wind resistance if using Stryd). But, on a closed loop course, the gradient somewhat cancels out.