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Re: DCRainmaker preview of Stryd running power meter [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
Bill Tyndale wrote:
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.


Worked out roughly, if 4% of a total power of 250 watts, to overcome air resistance at a running speed of 8 mph is 10 watts, then if there is an 8mph head wind which increases the speed through the air to 16 mph, the power to overcome wind resistance will not double but increase to approx 40 watts.


8 mph is hardly hurricane force but pretty normal. 8 mph is hardly sprinting. But it will take 40 watts more power to run into an 8mph wind than it would with an 8 mph tail wind.

If Stryd does not allow for wind speed it really isn't going to give you any better information than pace.

A man running presents a pretty big CdA, more than a cyclist, I can't see that the power to run into a cross wind isn't going to be substantial.

Anyone care to experiment with a mannequin in a wind tunnel?
Last edited by: Bill Tyndale: Jan 4, 16 7:57
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Re: DCRainmaker preview of Stryd running power meter [Bill Tyndale] [ In reply to ]
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Bill Tyndale wrote:
Anyone care to experiment with a mannequin in a wind tunnel?

As I said, Pugh addressed this question decades ago.
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Re: DCRainmaker preview of Stryd running power meter [iank] [ In reply to ]
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iank wrote:
Andrew Coggan wrote:
Bill Tyndale wrote:
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.


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.



A gadget which says you are using less power to run into a headwind than you are at the same speed with a tailwind is not just useless, but downright misleading - utterly stupid.

Furthermore, Stryd won't know if you are running behind another runner which eliminates 80% of the wind resistance, so again you will be seriously mislead by the power numbers in bunch running situations. It will give you power numbers approx 3% to 7% too high.

It really looks like you might as well use a watch.
Last edited by: Bill Tyndale: Jan 4, 16 9:32
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Re: DCRainmaker preview of Stryd running power meter [Bill Tyndale] [ In reply to ]
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Bill Tyndale wrote:

Worked out roughly, if 4% of a total power of 250 watts, to overcome air resistance at a running speed of 8 mph is 10 watts, then if there is an 8mph head wind which increases the speed through the air to 16 mph, the power to overcome wind resistance will not double but increase to approx 40 watts.


8 mph is hardly hurricane force but pretty normal. 8 mph is hardly sprinting. But it will take 40 watts more power to run into an 8mph wind than it would with an 8 mph tail wind.



Here's my math on this using my derivative of the di Pamprero model (offer is still out there, if you want this spreadsheet, just drop me an email) :



=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================
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Re: DCRainmaker preview of Stryd running power meter [Bill Tyndale] [ In reply to ]
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Bill Tyndale wrote:
It really looks like you might as well use a watch.

I don't have enough information regarding the stryd product to disagree with this; however, I do think there could be further insights derived from adding a good math model, a good field testing venue/process, and a good bathroom scale to your list.

=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================
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Re: DCRainmaker preview of Stryd running power meter [sciguy] [ In reply to ]
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sciguy wrote:
BikeTechReview wrote:
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


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


Thanks for reading, Hugh :-)

Yeah, this plot has been around for awhile:



I don't think the insight was anything new, but putting a ballpark number on it for an ironman type effort at the elite-ish level probably was at the time I did the analysis. Regardless, it was a fun and insightful exercise creating that plot! I hope others find it useful.

(ETA link to contour plot.)


=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================
Last edited by: BikeTechReview: Jan 4, 16 19:53
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Re: DCRainmaker preview of Stryd running power meter [BikeTechReview] [ In reply to ]
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BikeTechReview wrote:
Bill Tyndale wrote:

It really looks like you might as well use a watch.


I don't have enough information regarding the stryd product to disagree with this; however, I do think there could be further insights derived from adding a good math model, a good field testing venue/process, and a good bathroom scale to your list.


Scales yes.

I once checked over several years run times on regular routes. Simply dividing minutes by lbs then using that number to predict time over a route run at a lighter or heavier weight was remarkably accurate. It puts a spotlight on periods where there was improvement in fitness and when performance improved due to weight loss. Most of my runs were on undulating roads but I can predict times over flat courses just as accurately.

I didn't get anything like the same accuracy of prediction cycling, which isn't surprising, although there was obviously the same general trend of lighter = faster.

As we can so easily and accurately weigh and time ourselves over known courses or distances, I don't see there is a need to move from accurate weight and pace data to a 'dubious estimate of power' which does not take into account head or tail winds or reduced drag from running behind another runner and use that to track, plan and execute training.
Last edited by: Bill Tyndale: Jan 5, 16 2:09
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