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Re: DCRainmaker preview of Stryd running power meter [SwimGreg3] [ In reply to ]
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Oo! That's actually a very interesting idea! I wonder if they are indeed incorporating that. If they are, and reasonably well, I could see this product actually being more than just a relatively simple algorithm
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Re: DCRainmaker preview of Stryd running power meter [mopshiv] [ In reply to ]
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mopshiv wrote:
I wouldn't be too fast to discount it yet, ...Seems like a proper triathlete toy.. gadgets over training

Ha! So true.

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Re: DCRainmaker preview of Stryd running power meter [SwimGreg3] [ In reply to ]
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SwimGreg3 wrote:
Mike, I think your statement that power meters "ignore wind" threw me off. I think I now understand what you mean: that wind speed need not be known to calculate power.

I had initially assumed that a runner's acceleration vector in time would be unchanged by wind, and therefore unmeasurable by an accelerometer. However, I neglected to consider the period of a runner's gait in which they are not in contact with the ground. In stronger winds, the magnitude of accelerations and declerations required maintain a constant speed would be greater than in weaker wind. Therefore, perhaps it is possible to obtain accurate power measures using only a COM accelerometer.

Yes, I guess time will tell. What is also interesting is that if you know power, you can estimate calorie expenditure better than with heart rate. Of course, run economy varies, so that factor will always be an issue but the large variability in max heart rate makes heart rate based approaches questionable. This might be better.

Since accelerometers have become so small and cheap, I expect that we will see much more of this, with more companies getting into playing with the data. Should be really interesting!

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Re: DCRainmaker preview of Stryd running power meter [SwimGreg3] [ In reply to ]
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I realize I am being a bit pedantic here, but there is no direct measurement power meter.

An SRM etc has a device that emits an electrical charge based on how much it bends.

You then have to do math to turn that voltage into a guess about what the torque must have been, given assumptions about the material and the environmental conditions at the time.

And then you make a guess as to the velocity of the crank based on intermittent cadence signals from a magnet and an imperfect timing device (everything is imperfect!), and then you compute power.


Anyway everything is an estimate, the question is just how good or bad the estimate is.



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Re: DCRainmaker preview of Stryd running power meter [Mike Prevost] [ In reply to ]
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Mike Prevost wrote:
Frankly, I am not sure how the device can be verified at this point. Comparing the acceleration data to ground reaction forces using a treadmill with force plates is a good start, but I am not sure this tells the whole story.

I was thinking about this point yesterday.

Having a bit of experience in calibration, the only thing I can see is running with some sort of shoe with a 2d load cell in it.

I know some folks have built them for study with diabetics, but not sure if there is anything in sports.
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Re: DCRainmaker preview of Stryd running power meter [SwimGreg3] [ In reply to ]
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I wonder. I've spent some time on a treadmill with my Ambit3, which uses an accelerometer to try and figure out pace, and it's not close enough to be considered valid. Use a foot pod and it's great. Something on my wrist can't figure out what my feet are doing and I don't see how something on my back could either. If I'm running in the wind and apply force x with my foot against the ground and travel, say, 4 feet (just for illustrations sake) in one stride of my 30" leg, with a cadence of say 90 strides per minute, how can it tell the difference between me with my short legs applying more force to do that than someone else with longer legs? It's one thing for a foot pod accelerometer to give you speed accurately, this is measurable, but force, or work? Wrong tool for the job. It seems like it would be reasonable to use it as an approximation, but it should advertise the limitations explicitly, as the PowerCal does...that it's not an accurate representation, and that any resemblance to real numbers is purely coincidental.
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Re: DCRainmaker preview of Stryd running power meter [fisherman76] [ In reply to ]
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fisherman76 wrote:
I wonder. I've spent some time on a treadmill with my Ambit3, which uses an accelerometer to try and figure out pace, and it's not close enough to be considered valid. Use a foot pod and it's great. Something on my wrist can't figure out what my feet are doing and I don't see how something on my back could either. If I'm running in the wind and apply force x with my foot against the ground and travel, say, 4 feet (just for illustrations sake) in one stride of my 30" leg, with a cadence of say 90 strides per minute, how can it tell the difference between me with my short legs applying more force to do that than someone else with longer legs? It's one thing for a foot pod accelerometer to give you speed accurately, this is measurable, but force, or work? Wrong tool for the job. It seems like it would be reasonable to use it as an approximation, but it should advertise the limitations explicitly, as the PowerCal does...that it's not an accurate representation, and that any resemblance to real numbers is purely coincidental.

Of course, we don't have any real data yet, so to say that it is not an accurate representation at this point is pure speculation. Same as saying it is accurate. Also, the point is not to predict what the feet are doing, but rather, to predict what the overall center of mass is doing. Short legs and longer legs shouldn't really matter. It is trying to predict power, not speed. Same as the bike powermeter argument. The bike powermeter does not know if you are pedaling at 30 mph with a tailwind or 15 mph with a head wind. Does not matter. 250 watts is 250 watts. Speed or pace is another factor entirely, but we have lots of other ways to measure speed/pace.

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Re: DCRainmaker preview of Stryd running power meter [Mike Prevost] [ In reply to ]
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The amount of force required for a 6'4" runner to travel 4 feet with one stride as opposed to a 5'4" runner to travel the same assuming the same vertical oscillation, holding all else constant, cannot be the same. For one it's a tight gait and for the other a long stride, the longer stride requires more engagement and more energy. A power meter on a bike doesn't have anything to say about how efficient the rider is, it just measures the strain. An accelerometer has to make assumptions about efficiency to arrive at a power number, that's my point. Those assumptions are not just formulas, they vary between individuals, no?
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Re: DCRainmaker preview of Stryd running power meter [fisherman76] [ In reply to ]
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fisherman76 wrote:
The amount of force required for a 6'4" runner to travel 4 feet with one stride as opposed to a 5'4" runner to travel the same assuming the same vertical oscillation, holding all else constant, cannot be the same. For one it's a tight gait and for the other a long stride, the longer stride requires more engagement and more energy. A power meter on a bike doesn't have anything to say about how efficient the rider is, it just measures the strain. An accelerometer has to make assumptions about efficiency to arrive at a power number, that's my point. Those assumptions are not just formulas, they vary between individuals, no?

Measuring acceleration accounts for all of that. Think about it. And efficiency has nothing to do with it.

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Re: DCRainmaker preview of Stryd running power meter [Mike Prevost] [ In reply to ]
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I keep thinking about it and keep thinking the same, that acceleration is not the whole thing. An accelerometer on a semi hauling a full load would show it goes slowly from a full stop to traveling speed. It tells me nothing about the engine. Create the same acceleration profile in a Cooper and tell me you have the same power between the two. Please help me understand what's missing. I don't see how you can hold efficiency as a constant.
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Re: DCRainmaker preview of Stryd running power meter [fisherman76] [ In reply to ]
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fisherman76 wrote:
I keep thinking about it and keep thinking the same, that acceleration is not the whole thing. An accelerometer on a semi hauling a full load would show it goes slowly from a full stop to traveling speed. It tells me nothing about the engine. Create the same acceleration profile in a Cooper and tell me you have the same power between the two. Please help me understand what's missing. I don't see how you can hold efficiency as a constant.

Couple of things. I think we are talking about two different things with regards to efficiency. I am talking in terms of "economy" or energy expenditure for a given amount of external work. For example, for cycling, efficiency is about 20%. Meaning that about 20% of energy expended goes to making watts at the pedals. A power meter does not care about human metabolic efficiency and it should not. I don't know it this is the same efficiency you are thinking about.

For the second point, consider this. Power = force X distance / time. If a given acceleration pushes a heavy weight a short distance or a light weight a longer distance, the power is the same. Could be I am thinking about this wrong but I don't think so. If so, the engineers on here can straighten me out.

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Re: DCRainmaker preview of Stryd running power meter [Mike Prevost] [ In reply to ]
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Not metabolic efficiency. Force is acceleration times mass, Newton's second law. Can't make assumptions about mass from the back of a runners shorts with an accelerometer. Also can't disregard or make constant friction.
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Re: DCRainmaker preview of Stryd running power meter [fisherman76] [ In reply to ]
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fisherman76 wrote:
Not metabolic efficiency. Force is acceleration times mass, Newton's second law. Can't make assumptions about mass from the back of a runners shorts with an accelerometer. Also can't disregard or make constant friction.

Well, the only thing I know for sure is that the burden of proof is on the company. I don't have a dog in that fight. I think they are going to have to supply some data to really convince the skeptics. I just can't figure out how they would test it. It is an interesting idea though. Hope it works out for them.

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Re: DCRainmaker preview of Stryd running power meter [Mike Prevost] [ In reply to ]
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Agree 100% and I hope it works. You and I have the same goals here, I'm sure of it.
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Re: DCRainmaker preview of Stryd running power meter [fisherman76] [ In reply to ]
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Force is acceleration times mass, Newton's second law. Can't make assumptions about mass from the back of a runners shorts with an accelerometer.

Exactly. Stryd must utilize the runner's body weight if it is to provide accurate measurements.

I also agree with Mike in that it should not attempt to account for efficiency or economy. I expect a power meter to tell me the amount of power that I'm generating to drive me forward regardless of my efficiency.

But yes, the burden is, and always should be, on the claimant. It will be great if it stands up to rigorous cross examination.

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Re: DCRainmaker preview of Stryd running power meter [jackmott] [ In reply to ]
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I relish pedantry. You're right, if it requires a calculation it's not a direct measurement.

To be more precise, a cycling power meter measures (indirectly or otherwise) all components of power: torque and angular velocity. If the torque measurement requires certain assumptions then that is a limitation of the instrument which must be considered by the user when interpreting the measurements. Conversely I do not believe that the Stryd is capable of measuring all of the components of running power.

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Re: DCRainmaker preview of Stryd running power meter [Nick B] [ In reply to ]
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Nick B wrote:
About as useful as a Stages as a cycling power meter.

Meaning highly useful for pacing, tracking training load and better than GPS & elevation for calculating a normalized pace... and far more responsive and accurate than HR or RPE. But not as precise as a lab grade treadmill with a mask hooked up to your face to measure oxygen consumption. I'm waiting for the portable version of that for IM races.

I'd like to see more testing to get a better picture of variability.

I suspect that it will be like the Stages, and be fairly consistent in a steady stage and within a range of power near where you tested your FTP. But have some inaccuracy further out from there and during sudden changes in power.


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Re: DCRainmaker preview of Stryd running power meter [motoguy128] [ In reply to ]
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motoguy128 wrote:
Nick B wrote:
About as useful as a Stages as a cycling power meter.


Meaning highly useful for pacing, tracking training load and better than GPS & elevation for calculating a normalized pace... and far more responsive and accurate than HR or RPE. But not as precise as a lab grade treadmill with a mask hooked up to your face to measure oxygen consumption. I'm waiting for the portable version of that for IM races.

I'd like to see more testing to get a better picture of variability.

I suspect that it will be like the Stages, and be fairly consistent in a steady stage and within a range of power near where you tested your FTP. But have some inaccuracy further out from there and during sudden changes in power.

You know, there is a portable metabolic cart for measuring oxygen consumption. In fact, both sensormedics and Cosmed make portable devices you can run and bike with. I have used the Cosmed personally. Battery life is too short for Ironman though ; )

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Re: DCRainmaker preview of Stryd running power meter [motoguy128] [ In reply to ]
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motoguy128 wrote:
Nick B wrote:
About as useful as a Stages as a cycling power meter.

Meaning highly useful for pacing, tracking training load and better than GPS & elevation for calculating a normalized pace... and far more responsive and accurate than HR or RPE. But not as precise as a lab grade treadmill with a mask hooked up to your face to measure oxygen consumption. I'm waiting for the portable version of that for IM races.

I'd like to see more testing to get a better picture of variability.

I suspect that it will be like the Stages, and be fairly consistent in a steady stage and within a range of power near where you tested your FTP. But have some inaccuracy further out from there and during sudden changes in power.

Nope. Not better than NGP, not accurate for quantifying training load, way less useful than RPE, maybe as useful as HR.

This device is less useful than a Stages, which is about as useful as a HRM.
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Re: DCRainmaker preview of Stryd running power meter [Nick B] [ In reply to ]
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You generate more watts via the body , but it looks here they are trying to equate it to bike watts so people can be familiar with the numbers. The arms swinging generate watts, etc... bicycle is at an isolated point, with some power lost due to drive train. So on a similar effort bike work out of 220 watts, you are probably doing 360 running... this why running stress scores are higher


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Re: DCRainmaker preview of Stryd running power meter [Mike Prevost] [ In reply to ]
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Change battery in T2
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Re: DCRainmaker preview of Stryd running power meter [ In reply to ]
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A few thoughts...

Knowledge of a person's actual power output while cycling is immensely valuable, because:

1) mechanical power is what moves the bike down the road, and

2) cycling economy/efficiency does not vary dramatically between individuals, such that power provides a reasonable proxy for actual metabolic demand.

With that in mind, consider a running power estimator, i.e., one that relies on GPS, acceleromters, etc., to calculate power:

1) since power is being determined indirectly, the reported values provide no further insight into someone's actual performance than does knowledge of their pace and changes in elevation (although if accurate, estimated power does have the benefit of pinning a single number on things), and

2) running economy varies much more between individuals than does cycling economy/efficiency, such that the calculated power may not provide a valid/reliable indication of actual metabolic demand.

Combining the above with the fact that runners don't generally have to be able to rapidly change pace the way cyclists do, that they aren't as influenced by environmental conditions (e.g., wind), that they tend to utilize flat surfaces (tracks) for structured training, etc., and I can't see a running power meter having a significant impact on how people actually train and perform.
Last edited by: Andrew Coggan: Feb 2, 15 10:24
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Re: DCRainmaker preview of Stryd running power meter [Andrew Coggan] [ In reply to ]
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I'd disagree with Coggans comments above, in that if someone developed a true, 100% (or close to) accurate running powermeter, it would be extremely useful, and likely game-changing. Just like cycling, you could have accurate metrics that incorporate incline effects, pacing, etc.

I dont' think the differences in running vs group cycling racing make that big a difference. If anything, triathlon has shown that powermeters are probably even MORE helpful for steady-state effort racing than they are for pure bike racing where often times the powermeter pacing effects are meaningless since if you can't hold onto the pack in the acceleration, you're gone.

As it stands, using run pacing and elevation to calculate/estimate run efforts is just as bad as using something like an iBike. That said, I'm not sure I have faith that this new product will be anywhere near accurate enough to be valuable as a training/racing tool - for sure, it's not going to be in the same league as a bike powermeter, so in that regards, given the fuzziness of the data that will arise, it's likely it'll turn out like COggan predicts, meaning not so useful.

But make a 99-100% accurate running powermeter? Game changer for sure.
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Re: DCRainmaker preview of Stryd running power meter [Mike Prevost] [ In reply to ]
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Mike Prevost wrote:
motoguy128 wrote:
Nick B wrote:
About as useful as a Stages as a cycling power meter.


Meaning highly useful for pacing, tracking training load and better than GPS & elevation for calculating a normalized pace... and far more responsive and accurate than HR or RPE. But not as precise as a lab grade treadmill with a mask hooked up to your face to measure oxygen consumption. I'm waiting for the portable version of that for IM races.

I'd like to see more testing to get a better picture of variability.

I suspect that it will be like the Stages, and be fairly consistent in a steady stage and within a range of power near where you tested your FTP. But have some inaccuracy further out from there and during sudden changes in power.


You know, there is a portable metabolic cart for measuring oxygen consumption. In fact, both sensormedics and Cosmed make portable devices you can run and bike with. I have used the Cosmed personally. Battery life is too short for Ironman though ; )

Yeah, but the RQ's can run a bit high on those things... you won't be able to tell how many carb kcal's your burning to refuel properly.

To the others: It needs to know your body weight.

The above poster is a physiologist employed by PEARL iZUMi. However, statements are not made on behalf of nor reflective of PEARL iZUMI in any manner... unless they're good, then they count.
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Re: DCRainmaker preview of Stryd running power meter [SwimGreg3] [ In reply to ]
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Disclosure: I am on the Stryd team.

SwimGreg3 wrote:
For instance the device wasn't tested with varying wind conditions. Running into the wind obviously requires more power than running out of the wind at the same pace... I would be very surprised to find that the developers can account for wind speed in the algorithms they use to determine power output.


That is correct. We have a development plan to handle the influence of changes to wind properly, but don't have solid testing data on that yet. We will do our best to surprise you.

SwimGreg3 wrote:
Presumably the hardware is simply a multiaxis accelerometer.


There are several other sensors in it, including an air pressure sensor.

SwimGreg3 wrote:
Secondly, it wasn't tested on a lighter (or heavier) runner.


Stryd reports unit-mass power unless the runner enters his or her mass, in which case it reports absolute power. We don't yet know which most runners will prefer, but I personally suspect that unit-mass power will be used more commonly because it can be used to set training zones and it is easier to usefully compare the unit-mass power values of different runners.

SwimGreg3 wrote:
All other things being equal, a heavier running should require more power to maintain the same pace.


Right, and based on our testing so far, we believe Stryd would produce the right result in that case.

SwimGreg3 wrote:
I'd like to see a much more thorough testing before I'd consider purchasing one.


That's why we are presently planning to cap the initial production round so we can work closely with the first group of 1,000 owners. Our tests with runners have been going well so far, we believe Stryd is at the point where people can benefit from its use, but we want get more data and feedback before scaling up production. Also, the hardware platform we developed is surprisingly flexible. As we learn more from the first owners, we will be able to remotely upgrade their devices. We will do our best to treat our initial supporters right.

SwimGeg3 wrote:
That said, a running power meter is a super cool idea... I hope that people continue to develop these devices.


Thanks. If enough people see the potential, we will do that.
Last edited by: robert-stryd: Feb 2, 15 19:53
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