First power meter - guidance and feedback please

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Alex Simmons/RST
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Re: First power meter - guidance and feedback please

Postby Alex Simmons/RST » Sun Apr 01, 2018 9:18 am

Certainly the power meter is an accurate tool for calculating mechanical work done, and via that an estimate of energy metabolised while exercising. You can probably get an estimate within a 10% accuracy range most of the time which is more reliable than other day to day means such as online estimators, heart rate monitors.

As a ROT, energy expended in kcal = 1.05 - 1.15 x mechanical work done in kJ.

IOW if you take the kJ reading from your power meter, add 10% and call that Calories metabolised, you'll most likely be in the right range give or take 5%.

While there are differences, on average, in efficiency between untrained, recreational and trained cyclists, those differences are smaller than the individual variability of efficiency between riders at each level. IOW a recreational rider can still be more efficient than a trained cyclist.

That's because inherit biochemical factors, muscle fibre type mix and the duration and relative workload of effort are more influential on one's individual GME than various and often purported pedalling technique improvements - due to the fact that cycling is a motion performed without many degrees of freedom.

You can be more precise with metabolic energy demand from cycling if:
i. you know your GME via gas exchange analysis performed in a lab, and
ii. your cycling is mostly relatively steady state.

That said it is possible to determine VO2max (and hence GME) with reasonable accuracy using a good power-duration model if you have sufficient quality mean maximal power data across a decent range of duration (e.g. from 5s to 3600s). But this is relatively new and its application requires care in understanding limitations (usually a result of factors influencing the quality of data inputs and a wise choice of model).

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Re: First power meter - guidance and feedback please

Postby CKinnard » Sun Apr 01, 2018 11:57 am

Gas exchange analysis is confounded by diet composition, bodyfat %, fat burning adaptation, and insulin resistance.

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Re: First power meter - guidance and feedback please

Postby Arbuckle23 » Sun Apr 01, 2018 12:05 pm

CKinnard wrote:Gas exchange analysis


I have plenty of gas :)

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Re: First power meter - guidance and feedback please

Postby Alex Simmons/RST » Sun Apr 01, 2018 12:48 pm

CKinnard wrote:Gas exchange analysis is confounded by diet composition, bodyfat %, fat burning adaptation, and insulin resistance.

So?

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Re: First power meter - guidance and feedback please

Postby CKinnard » Mon Apr 02, 2018 12:26 pm

Alex Simmons/RST wrote:
CKinnard wrote:Gas exchange analysis is confounded by diet composition, bodyfat %, fat burning adaptation, and insulin resistance.

So?


These are factors that effect GME calculation and result.

Pedaling technique has been too casually dismissed in its influence on GME. i.e the influence of cadence on climbing efficiency.

And more significant inputs to GME are a higher % of total blood flow (cardiac output) to key cycling muscles, and glycogen storage in same.
Experienced riders on average are likely to have an advantage in both.

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Re: First power meter - guidance and feedback please

Postby Alex Simmons/RST » Mon Apr 02, 2018 2:50 pm

CKinnard wrote:
Alex Simmons/RST wrote:
CKinnard wrote:Gas exchange analysis is confounded by diet composition, bodyfat %, fat burning adaptation, and insulin resistance.

So?


These are factors that effect GME calculation and result.

Pedaling technique has been too casually dismissed in its influence on GME. i.e the influence of cadence on climbing efficiency.

And more significant inputs to GME are a higher % of total blood flow (cardiac output) to key cycling muscles, and glycogen storage in same.
Experienced riders on average are likely to have an advantage in both.

Again, so what?

In the context of this thread, i.e. guidance on using a power meter, it's hardly pertinent.

Yes, elite riders are, on average, a little bit more efficient than trained, recreational and untrained riders. So what?

The differences in efficiency between such rider levels is not actually all that much (~10% on average), and they pale when compared with the differences in sustainable power output for riders across the capability spectrum (which are of the order of ~300-400%). IOW differences in efficiency only account for a small proportion of the differences in physiological capability. And our ability to positively influence GME is rather limited because it is dominantly an inherited trait.

When testing efficiency there are typically controls wrt the relative intensity one tests at, and what pre-test controls are put in place, such as diet, fatigue, glycogen levels and so on. Yes efficiency varies with cadence and other factors affect it on an acute and chronic basis. Environmental conditions or hydration status for instance. Yawn. Tell us something new or useful in context of this thread.

Cadence is not "technique". It's just a measure of crank rotational velocity.

Indeed cadence is not something we can actually independently control, despite what one might believe.

What we can control is our level of effort (power output) and gear choice. Cadence is then an outcome of those choices and the resistance forces acting against us at the time.

As for technique being lightly dismissed, meh I just refer to the published science which demonstrates changing "technique" from that which develops naturally really doesn't do all that much.

In any case we don't typically pedal at cadences equated with the highest efficiency (we tend to pedal more quickly that that) since maximising efficiency isn't typically the objective of cycling (certainly not in any competitive or performance sense). What does matter (physiologically) is the ability to sustain power output over durations of relevance. Fortunately that's what a power meter tells us, and is what makes it really useful.

In any case, esoteric discussion of GME is not really of much value here.

Information about using the power meter in a productive manner is the topic.

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Re: First power meter - guidance and feedback please

Postby MichaelB » Mon Apr 02, 2018 3:40 pm

I dunno what GME is ?

Anyway, even if I could work it out with a power meter, I wouldn't work it out.

Far beyond what this thread was all about anyway. BoT. :-)

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Re: First power meter - guidance and feedback please

Postby Alex Simmons/RST » Tue Apr 03, 2018 7:07 am

MichaelB wrote:I dunno what GME is ?

Gross Mechanical Efficiency.

It's the ratio of mechanical energy applied to the cranks of the bicycle to the total energy metabolised by our body.
Approximately 1/5th of the energy we metabolise ends up reaching the cranks. The vast majority of the balance is given off as waste heat.

MichaelB wrote:Anyway, even if I could work it out with a power meter, I wouldn't work it out.

Far beyond what this thread was all about anyway. BoT. :-)

That was my point. Focus on power as it's the integral of all the underlying processes and factors, and is what matters.

For those interested in using the power meter for keeping an eye on their energy balance (i.e. food calories in, exercise and base metabolism calories out), then just use the simple method I outlined earlier for estimating the energy demand while cycling.

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Re: First power meter - guidance and feedback please

Postby Arbuckle23 » Tue May 22, 2018 6:48 pm

At the risk of Alex telling me "I told you so" :) The Powerbeat has been sent back.
Had problems with the first sensor, so Watteam sent me another. It too gave problems.
Getting dropouts all the time, readings all over the place, even on a trainer
Contacted Pushys and returned to them for a full refund.
Big Kudos's to Pushys, no problems in returning when I voiced my dissatisfaction with the product.
But the little taste of power now has me in.
Spent a little :wink: :lol: :oops: more on pedal based Favero Assioma.
Been using for a week with no problems, very happy. Solid as a rock.

Riding with/to power is such an eye opener. A lot more to learn, but will enjoy the learning.

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Re: First power meter - guidance and feedback please

Postby MichaelB » Tue May 22, 2018 9:51 pm

Glad it worked out in the end.

Presume single sided ?

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Re: First power meter - guidance and feedback please

Postby Arbuckle23 » Wed May 23, 2018 6:54 am

I decided that I would blow the budget right out of the water and got dual sided :oops: .
All the chat about single sided got to me, upgrading later would cost even more.
The good thing is that the pedals can fit my backup bike now. Different crankset types on each bike.

The interesting thing I have learnt about knowing both sides, is that I consistently seem to be 52/48 L/R. And slightly more again on the left when working harder.
Being right handed and useless with my left hand and foot I would have thought it should have gone the other way?

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Re: First power meter - guidance and feedback please

Postby MichaelB » Wed May 23, 2018 8:37 am

Arbuckle23 wrote:I decided that I would blow the budget right out of the water and got dual sided :oops: .
..


:lol: :lol: Get War Office approval ?

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Re: First power meter - guidance and feedback please

Postby Arbuckle23 » Wed May 23, 2018 9:50 am

MichaelB wrote: :lol: :lol: Get War Office approval ?


Ssh :wink:

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Re: First power meter - guidance and feedback please

Postby Alex Simmons/RST » Wed May 23, 2018 11:33 am

Arbuckle23 wrote:I decided that I would blow the budget right out of the water and got dual sided :oops: .
All the chat about single sided got to me, upgrading later would cost even more.
The good thing is that the pedals can fit my backup bike now. Different crankset types on each bike.

The interesting thing I have learnt about knowing both sides, is that I consistently seem to be 52/48 L/R. And slightly more again on the left when working harder.
Being right handed and useless with my left hand and foot I would have thought it should have gone the other way?

Power asymmetry is variable and often unrelated to what is our natural side.

But to put it into context, there were times when I was measured as left side dominant while at an easy endurance power level which considering I'm a left below knee amputee may be a little surprising. As the power level went up, I evened up in my power balance.

One of the things with meters which measure each crank/pedal independently is you now actually have two power meters, each with potential error or bias in their readings. It's also twice as many things to go wrong :)

All good fun.

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Re: First power meter - guidance and feedback please

Postby Alex Simmons/RST » Wed May 23, 2018 11:35 am

Arbuckle23 wrote:At the risk of Alex telling me "I told you so" :) The Powerbeat has been sent back.

Bummer. But what matters most is that the after sales support backed you up. That's the bit I worry about with the newer players. Perhaps less so early on but later when the weight of longer term financial viability begins to bite.

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