Though experiment aside, Is there a way to measure or infer impact forces? As opposed to forces to overcome?

Maurice

All objects in earth's orbit, unless they have a limitless supply of fuel, will eventually fall to earth due to orbital decay, even if they do reach orbital velocity and go into orbit they will eventually fall to earth.

You need to be looking at thrust to weight ratio not power. It's a bit like confusing strength with power, don't confuse thrust with power.

I told you running power meters would waste a lot of people's time.

An interesting and entertaining thought experiment though.

Not to nitpick but the moon is moving further away every year. ;)



So QED. But where did you prove it? All I've read are critiques of Coggan's posts. I'm simply interested in whether or not Stryd is viable tech. Ignoring Coggan's assertions, where do you think is the point where Stryd's approach fails?

[Sorry Trev. I've edited as I realized my post was coming off as an attack whereas I'm actually just curious.]

They say the moon is moving away from Earth due to tidal bulge which doesn't apply to Andrew's man in the thought experiment.

I'm just ribbing Andrew because he seems to have changed his mind.

Andrew Coggan wrote earlier in this thread, "I can't see a running power meter having a significant impact on how people actually train and perform.

Because there's nothing a runner could accomplish using a powermeter that couldn't already be accomplished using a measured distance, a watch, and some common sense."

I'm pursuaded by his earlier arguments like those above.

If Sryd measures actual power there might be a use in refining technique and style to get more speed out of a given power.

But whatever the power in the end it will boil down to whatever technique and style makes a given speed feel easier.

Stryd does not measure power directly but looks at exceleration, gradient etc, then estimates power. It's entirely possible to generate more power but fail to increase speed because you are running inefficiently. Can Stryd tell the difference between running efficiently along the ground and running in a manner which wastes power running upwards too high and landing with more force covering less ground with each stride?

Interesting article here.

http://athletictimemachine.com/...6/thoughts-on-stryd/

Watts:MPH ratio?

I'm not sure if Stryd measures power in such a way as to do this in a useful way as it isn't measuring forces but is using speed / exceleration to estimate watts.

I'm reluctant to ignore easily gathered data but I can see people being mislead by the watts numbers or wasting a lot of time playing with the data but not putting the info to good use.

Will it help people train better? If not it's a waste of time. More power does not mean more speed. Concentrate on speed.

As Andrew Coggan said earlier in this thread,

"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. "


""*Note that an important difference between running and cycling is that the economy of movement is much more variable in the former than in the latter. Also, muscle use varies more in the former than in the latter, e.g., even if you keep your estimated power constant when transitioning from the flats to up hill, you will be placing more demand on your quads as a result. So, should you really be aiming for an iso-power effort, or an iso-metabolic one? ""



How does Stryd measure speed / distance and how accurate is its measurement of speed and distance?

Yes, although that's just my perception. I haven't done any proper testing to know if that's true

Say what you will about the product, the one thing I love about DC's reviews is that he leaves no stone unturned. Very very in depth.

With that being said, I aint wasting my money on one of these

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When all is said and done. More is usually said than done
Ba Ba Booey

It doesn't.

You're getting to the heart of the matter with power for running. The answer to your question is no. At least, not yet. But analysis for this is coming soon, very soon.

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Jim Vance
http://TodaysPlan.com.au (Disclosure: I am contracted with Today's Plan)
http://www.CoachVance.com/
Twitter @jimvance

I don't own the stryd device (yet!), but have produced actionable running power based information using the di prampero running model (that is available for free in the literature) for the better part of the last 10 years:

http://www.biketechreview.com/...thlon-pacing-sort-of


http://www.biketechreview.com/...555-triathlon-pacing


Although I haven't written about it on BTR lately, I've used this model for setting pacing targets on "lumpy" race courses I've never run on before:


https://www.strava.com/activities/283534744


If anyone wants the spreadsheet I've created based on the di Prampero model, shoot me an email at kraig@biketechreview.com and I'll send you a copy.


In summary, I find the di prampero model, combined with my PE, a good field test venue, a stopwatch, and a bathroom scale, very handy for assessing my current fitness and setting achievable running goals/performance targets. YMMV, of course, and I look forward to playing with the stryd device - but this stryd "fun" might have to wait until it becomes available on the used market (like the iBike I purchased and then toyed with/evaluated).

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Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
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Ignoring the dependence of orbital velocity on planetary radius (on a small planet the orbital velocity would be much smaller) your experiment does hit on the problem of aerodynamics in power calculations a la stryd.

The orbital velocity of earth is about 29800 m/s and to keep things simple that represents a LOT of aero drag in the atmosphere. Totally remove this atmosphere on the small planet and all the drag disappears which drastically change the behavior of the person between the two scenarios. So in situation one velocity can be maintained without acceleration due to there is not drag to counter the original force of the step. On earth maintaining a velocity while running will always require additional acceleration because the atmosphere does exists and force can only be applied at discrete points. In any case converting power based on acceleration and velocity requires having an excellent constraint on the force of air resistance and large errors will creep in if air resistance changes. My guess is this is where wind speed comes into play and that in wind conditions the Stryd won't work well.

On a side note what Stryd needs is some way do differentiate vectors of human acceleration from terrain. In other words it needs to be able to differentiate the components of vertical acceleration due to bad running form (bouncing up and down) from vertical acceleration due to changing elevation. This could be done by looking at the total movement of the subjects center of mass relative to the net movement the center of mass. Such a metric would diagnose bad form and get around some of the issues previously brought up in the thread.

Or IOW, wind resistance causes you to slow down more during the flight phase, requiring that you re-accelerate yourself more during the stance phase to maintain a constant velocity. Wind resistance also resists that acceleration during the stance phase. I therefore believe that the Stryd therefore doesn't need a separate wind sensor to account for the (generally rather small) effect of aerodynamic drag while running.

When a runner passes you it's surprising what a gust of air you feel as they go by.

It may be minimal but it still requires some power to move through the air.

Does Stryd account for this power?

Back in the 1970s, LGCE Pugh measured the effects of wind on the energy requirements of running, by placing a treadmill in a wind tunnel. Under most conditions, <5% of total energy is expended against the wind* - only at very fast running speeds (e.g., Olympic sprinter) or under hurricane-like conditions does it really rise much above this.

As I attempted to illustrate with my thought experiment and as I described just a few posts above, I believe that Stryd's approach to measuring (positive) power does account for wind resistance (even if they won't claim so themselves).

*Thus explaining the 1% rule-of-thumb for treadmill running....that amount of grade increases energy costs by ~4%, thus better equating speed between indoor and outdoor conditions.

I've read several times that aero drag is a small effect in running, but the position of a runner must lead to CdAs close to 0.5 m^2. Even at 5 m/s, that's equivalent to 30-40W at sea level. With a 5 m/s head wind, that could climb to 150W.

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AndyF
bike geek

Entirely anecdotal, but consistent with Stryd's own claims, is my experience with it. I've noticed that running in windy conditions actually tends to produce the opposite power numbers of what you'd expect...higher power for lower RPE at same pace with a tail wind, lower power into headwind. My best guess is that because it measures/estimates force using accelerometer, there's not really a way to distinguish whether the forward/backward force is coming from me or the wind.

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IG: idking90

There appears to be a lot of confusion between air resitance and 'aerodrag/wind resitance' which is also where I think Stryd fails.

Air resistance is a frictional force determined by how fast you move relative to the air. Assuming stationary air (no wind) the force of air resistance is small over the speed changes on the scale of running. That is to say a runner experience minimal additional air resistance when running at a 6min/mile versus a 7 min mile. The same is true for cycling in that small speed changes at overall low speed result in minimal aero drag changes. Now once the wind starts blowing its a different ball game because the magnitude of speed changes are far far greater. The difference between a 15mph tail wind and 15mph head wind is equal to a 30 mph change in the relative motion of the runner and the wind. Think riding a bike a 10mph and then at 40mph and its clear there is a significant change in force. Your calculation are correct in this respect.

I don't understand how Stryd corrects for this effect. Yes its easy to correct for air resistance if you assume the subjects total velocity is equivalent to the relative difference of their velocity and the velocity of the air. In fact at cycling speeds this is often a good assumption which is why small yaw angles are most relativistic for aero testing. At running speeds however wind speed often exceeds total running velocity.

Kraig,

Thanks for the link to the post above. I'd never seen your thoughts on this and find them pretty darn interesting and certainly worth discussion as well as further investigation. It's pretty obvious that the majority of triathletes over allocate effort on the bike side of the equation and the development of more tools or guidelines for the allocation would seem prudent.

"What does this all tell me? I think it means that getting real small aerodynamically on the bike (since you really don't have to put out big power) becomes even more important -> just gotta progress on the deal so you can get comfy over time. I think this takes diligent, hard, consistent work to get aero and comfy - it doesn't happen overnight.

I also reckon that one's run speed/power is the limiter on the deal -> that will steer how slow/low power one should go on the bike.

BTW, this analysis changed my gut feeling on how to pace an ironman -> I gut felt an even split was the way to go. I reckon I was wrong..."

Hugh

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Genetics load the gun, lifestyle pulls the trigger.

I think several things explain the apparent discrepancy:

1) 5 m/s is PDQ, requiring that you either be a pretty good runner (e.g., 5 km in 16:40) and/or that winds at ground level are pretty high;

2) for perfectly-logical physiological reasons, the (positive) power output of a runner is significantly higher than the (net) power output of a cyclist (i.e., the demoninator is larger than you are used to seeing); and

3) relative energy cost and relative power requirements aren't quite the same thing.

You know, I believe I have seen you mention this before, but until reading the above it didn't really click. I now realize that I've been viewing things from the perspective of the environment (ground), e.g., as if the runner were running across a force plate. Stryd, however, relies on Newton's 2nd law, which certainly complicates things. I'm therefore going to take back what I said, at least until I've had the chance to experiment/ruminate a bit more.

I'm quite a light chap and I definitely notice the difference running into a stiff headwind versus a tasty tailwind. Ideally the power numbers would reflect this.

I haven't tested, but my understanding is the Stryd will give me the same power number for the same pace in both conditions. My understanding (which I'm trying to double check) is that Coggan, you're saying that the Stryd model does account for wind resistance but not varying wind resistance?

I don't know how Stryd calculates power (although I can guess), but up until moments ago I would have said that it accounts for the power required to push forward through the air. Now, I see it is more complicated

Thank you -- that completely makes sense.

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AndyF
bike geek

You're welcome!

(For the benefit of others: to run at 5 m/s requires a power output of ~5 W/kg.)

Yea, I live in a completely flat place, so I don't hills besides overpasses to compare too, but it can be pretty windy. If nothing else, I have been able to "wake up" the Stryd by just shaking it a lot and my watch will show 1,000+ W on it when I do that.

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IG: idking90