newbie using wattage

Is it really harder or is it just an illusion. My question to you would be, what is your heart rate on the hills vs. flats?

Quoted post said:

Originally posted by tmctguer
on the flats, i was finding it difficult to maintain over 225 watts. part of this could have been due to fatigue from the hill. but it just seems like it is harder to maintain higher wattage on flats.

any advice or observations here?

This has been touched on but it could be several things...what gearing were you using, was the wind at your back, was it even all that flat? There's a section of road I ride on from work that looks flat but I know from topos that it actually loses elevation...so it's difficult to keep w's up on that stretch.

I generate, well according to my HAC4, 300+ W for short bursts on the hills but if I tried to do that consistently on the turbo I would collapse. That's why I long for a Powertap or similar, so that I can see/understand exactly what is going on. Will it make me a better/faster cyclist I don't know

Quoted post said:

Originally posted by tmctguer

about a week ago, i installed a polar power device on my bike. i am fascinated about wattage as a measure of my rides, as opposed to just HR or speed.

there are several long steep climbs i regularly ride. one of them is 1.6 miles long at 8% gradient. it usually takes me between 11 - 12 minutes to climb it. until i got the power meter, i just rode using MPH as my guide.

this AM, however, i attempted to keep a constant wattage for as long as possible during the climb. i was able to maintain approx. 350 watts for approx. 6 minutes or over 1/2 of the climb. it was difficult, so i decended the backside and rode on some flats to cool down.

on the flats, i was finding it difficult to maintain over 225 watts.

The problem could very well be with your powermeter. The Polar S7X0 is notorious for providing different - sometimes wildly different - power values depending on gear/chainline. On most bikes, you can get reasonable (+/-5% as claimed) data by positioning the chainstay sensor *very close* and as parallel as possible to the chain (so close that the chain may drag in certain gears). Unfortunately, positioning the sensor in the right place usually requires making some sort of custom mount, and it may require quite a bit of fiddling and riding up a hill of known grade to make sure you're getting accurate results no matter what your chainline. (You usually can't use a trainer or rollers to make life simpler, since the chain tension sensor almost always picks up other regular vibrations in such a situtation, e.g., lumps in the tire, etc.)

That is a crazy device!

FWIW, my (equally flawed) HAC4 gives me similar proportional readings. I sometimes climb for extended periods at 240W+, but trying to match that on the flats leaves me gassed. More like 180W there.

That, along with why it's even harder on a stationary bike/trainer, are among the world's greatest mysteries. Ranks right up there with crop circles, Bermuda Triangle, that kinda stuff.

Quoted post said:

Originally posted by acoggan
The problem could very well be with your powermeter. The Polar S7X0 is notorious for providing different - sometimes wildly different - power values depending on gear/chainline.

Only when mounted on a trainer...All the "on road" data I've seen doesn't show this problem (as compared to Powertaps or SRMs).

Quoted post said:

Originally posted by acoggan
On most bikes, you can get reasonable (+/-5% as claimed) data by positioning the chainstay sensor *very close* and as parallel as possible to the chain (so close that the chain may drag in certain gears).

"Very close" only means no more than 30 mm in the gear combination that puts the chain farthest away. I have mine set at 30 mm in my large chainring, second from the largest cog (on 9 speed) since going "big, big" ends up in too much crossover so I don't use that gear anyway. This means that the chain will rub in the small chainring and the 2 smallest gears...but again, I don't ever use those gears because of the extreme crossover.

Parallelism makes no difference...the main thing is that the chain passes over the sensor area at all times. The angle of the sensor relative to the bike centerline is actually more determined by getting the cadence sensor portion close enough to the crankarm to sense the cadence magnet.

Quoted post said:

Originally posted by acoggan
Unfortunately, positioning the sensor in the right place usually requires making some sort of custom mount, and it may require quite a bit of fiddling and riding up a hill of known grade to make sure you're getting accurate results no matter what your chainline. (You usually can't use a trainer or rollers to make life simpler, since the chain tension sensor almost always picks up other regular vibrations in such a situtation, e.g., lumps in the tire, etc.)

A couple of squares of high durometer neoprene sheet and some zip ties and my installation was complete. As far as testing goes...I'm typically within 5 W of the estimate from www.analyticcycling.com for an 8% climb I do almost every week.

Quoted post said:

Originally posted by Aztec
That is a crazy device!

FWIW, my (equally flawed) HAC4 gives me similar proportional readings. I sometimes climb for extended periods at 240W+, but trying to match that on the flats leaves me gassed. More like 180W there.

That, along with why it's even harder on a stationary bike/trainer, are among the world's greatest mysteries. Ranks right up there with crop circles, Bermuda Triangle, that kinda stuff.

"Equally flawed"? Not even close. The Polar is actually a measurement based on chain tension...the HAC is just an educated guess.

The difference you see is because the HAC's "guesstimate" has, by my experience, a pretty low CdA value built into it. Of course, it also can't account for headwinds or tailwinds either. Add to that the fact that it's display only updates in 20W chunks and you can see that it's power "calculation" is really just for entertainment purposes only, especially on flats and rollers.

It actually isn't _that bad_ on relatively steep climbs...it just doesn't have a lot of resolution.

Quoted post said:

Originally posted by Tom Anhalt
Only when mounted on a trainer...All the "on road" data I've seen doesn't show this problem (as compared to Powertaps or SRMs).

Yes, all the data *that have been reported* do seem to show reasonable accuracy. However, not all that much data has actually been reported, and some of it has been generated by/with the help of one of the Cote brothers, who obviously have a vested interested in the success of the Polar powermeter. On the flip side, you have people like Dave Harris who have very low opinions of the Polar powermeter (based on first hand experience), and prominent coaches (like Ed Monnier) who refuse to work with athletes who use one. I think the takeaway message is that, unless the person installing the device is somewhat technically adept and takes the time to verify that it is giving reasonable numbers, you can't be completely confident in the data.

Quoted post said:

As far as testing goes...I'm typically within 5 W of the estimate from www.analyticcycling.com for an 8% climb I do almost every week.

That's good, but can you ride up that 8% climb using every one of your gear combinations, to be certain that you don't have at least some chainline dependency to your numbers? Unless you're exceptionally powerful and/or can pedal at very low cadences, then the answer is probably not...which is one of the things I see as being most limiting about the Polar approach, i.e., the accuracy of the data is dependent upon the installation, yet there's no easy way to be 100% certain you've got the sensor in the "sweet spot".

Quoted post said:

Originally posted by acoggan
Yes, all the data *that have been reported* do seem to show reasonable accuracy.

Well...that's all I can go on, now isn't it? It's hard to form an opinion on *unreported* data.

Quoted post said:

Originally posted by acoggan
However, not all that much data has actually been reported, and some of it has been generated by/with the help of one of the Cote brothers, who obviously have a vested interested in the success of the Polar powermeter.

The data that was generated and posted by JJ Cote is on Robert Chung's site comparing the Polar to a Power Tap. However, there is also the data taken by Kraig Willett with the Powertap, Polar, and SRM all together. Additionally, there's a published study comparing the Polar to an SRM.

Quoted post said:

Originally posted by acoggan
On the flip side, you have people like Dave Harris who have very low opinions of the Polar powermeter (based on first hand experience), and prominent coaches (like Ed Monnier) who refuse to work with athletes who use one.

Dave Harris's case is a special situation in that he was using it on a mountain bike with knobby tires. Some of the same vibrational issues that affect the Polar's trainer performance were evident in his readings during on-road training.

Quoted post said:

Originally posted by acoggan
I think the takeaway message is that, unless the person installing the device is somewhat technically adept and takes the time to verify that it is giving reasonable numbers, you can't be completely confident in the data.

I agree that it's not a "plug and play" type device. However, you have to agree that none of the power meter options are to that extent either. There's always some sort of calibration, resetting offsets, etc. that takes place with any of the current offerings.

Quoted post said:

Originally posted by acoggan
That's good, but can you ride up that 8% climb using every one of your gear combinations, to be certain that you don't have at least some chainline dependency to your numbers? Unless you're exceptionally powerful and/or can pedal at very low cadences, then the answer is probably not...which is one of the things I see as being most limiting about the Polar approach, i.e., the accuracy of the data is dependent upon the installation, yet there's no easy way to be 100% certain you've got the sensor in the "sweet spot".

Aahh...but I don't need to repeat this test in all gears. First, based on the Polar's method of operation, if I'm getting good numbers with the chain at it's furthest position from the sensor, it'll be good across the range (as long as it's not mounted on a trainer, of course). There can't be any proportional type errors (except if your initial measured inputs have errors). The "spacing" issues come about when the vibrational signal is too weak (i.e. when the chain is furthest away). This case is covered by this hillclimb test. Then, looking at the "head to head" on-road data mentioned above, there's no gear by gear discrepancies as compared to other power meters. Therefore, I feel reasonably confident in the numbers I'm seeing.

All I can say is that in my relatively limited experience (>4 months now) the Polar Power module has been "bullet proof" in it's performance. In fact, I've had more issues with the HR monitor performance than with the power measurement....Of course, what am I doing still looking at HR, huh?

Quoted post said:

Originally posted by Tom Anhalt
Additionally, there's a published study comparing the Polar to an SRM.

I don't mean to completely 'diss' the Polar powermeter, since I've never used one and some people (like yourself) seem to get good results with it. However, based on the experiences of people like Ed Monnier I can't help but have certain reservations about them. That point-of-view is actually reinforced by the study you cite above, which concluded that the S710 was "...a useful device for recreational cyclists but not for elite cyclists or scientists who require a greater accuracy and validity." This conclusion was based on the fact that not only did the S710 read consistently higher (by 7.4 +/- 5.1%) than the SRM to which it was compared, but also that this difference was both power and cadence dependent. (See http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12740731) Thus, at present I only recommend the Polar powermeter to people who already own everything except the power module itself (thus making the cost of "training by power" considerably less than going with one of the other systems).

Quoted post said:

Originally posted by acoggan
I don't mean to completely 'diss' the Polar powermeter, since I've never used one and some people (like yourself) seem to get good results with it. However, based on the experiences of people like Ed Monnier I can't help but have certain reservations about them.

Well...at least I'm glad you're open to the alternative argument. BTW, can you relate what experiences caused Ed Monnier to issue his blanket edict? I'm always curious as to what difficulties people find, if anything as a "heads up" for potential future problems.

Quoted post said:

Originally posted by acoggan
That point-of-view is actually reinforced by the study you cite above, which concluded that the S710 was "...a useful device for recreational cyclists but not for elite cyclists or scientists who require a greater accuracy and validity." This conclusion was based on the fact that not only did the S710 read consistently higher (by 7.4 +/- 5.1%) than the SRM to which it was compared, but also that this difference was both power and cadence dependent. (See http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12740731) Thus, at present I only recommend the Polar powermeter to people who already own everything except the power module itself (thus making the cost of "training by power" considerably less than going with one of the other systems).

This only points out the dangers of making conclusions based on just paper abstracts. I don't know if you've seen the full text of this paper, but I have a copy and I think they missed the entire issue of the "on trainer" performance and let it mislead some of their conclusions. For example, the study consisted of two sets of tests, an "on road" test and a "lab test". The "on road" test consisted of six uphill 6 min trials of varying intensities and body positions. In this case, the power measured by the Polar varied from the SRM by the quoted 7.4 +/- 5.1%. Since this variation is a pretty constant percentage across power levels and test trials/subjects, my suspicion is that something wasn't entered into the Polar correctly during the initial setup, or perhaps the SRM wasn't calibrated correctly. In fact, the coefficients of variation during these trials were almost identical for the Polar and SRM.

The second test consisted of 3 trials with the bikes attached to a standard wind trainer. The wattage was held at 150W and the cadence was varied between 60, 90, and 110 rpm for the 5 min. trials. In this case, they found that the differences in power readings increased with increasing cadence. Perhaps unbeknownst to them, this test is almost ideal for demonstrating the Polar's "on trainer" difficulties. In my experience, and judging by comments from the Cotes, one "achilles heel" of the Polar sensor is relatively low power/ high cadence conditions. Under this condition, the vibration signal from the chain tension is relatively low, while the chain speed signal frequency is "dangerously" close to the expected tension signal frequency. This can allow the Polar to "lock on" to the wrong signal. Couple this with the known vibrational problems, and I think it's clear that this second test just tells us it doesn't work well on a trainer.

Actually, on the questions of reliability and repeatability, here's another quote from the study: "The present results showed also that the S710 is a highly reliable powermeter. The repeatability of S710 appears better than some other devices (e.g. Kingcycle, Politechnica, Monark) available for recording power output, but similar to the SRM." 🙂

BTW, even if you don't own the S710/S720 already, it is still potentially the cheapest way to get power readings. I bought a brand new S710 and used power module and my total cost was less than $300...including what I paid for CyclingPeaks! That's tough to beat.

Quoted post said:

Originally posted by Tom Anhalt
This only points out the dangers of making conclusions based on just paper abstracts. I don't know if you've seen the full text of this paper

I never cite a paper I haven't read.

Quoted post said:

Originally posted by acoggan
I never cite a paper I haven't read.

I know there are some drawbacks to the mini comparison I did today but I will site the data anyway.

My team mate has a Polar. He wanted to do intervals with me and wondered if it was giving him accurate readings to set his zones. I hooked up my PT to his bike as well, made sure it was calibrated, and off we went. 20 min later we stopped and checked the 2 readings. The Polar said he had averaged 265w. The PT said 240w.

Quoted post said:

Originally posted by J-Law
I know there are some drawbacks to the mini comparison I did today but I will site the data anyway.

My team mate has a Polar. He wanted to do intervals with me and wondered if it was giving him accurate readings to set his zones. I hooked up my PT to his bike as well, made sure it was calibrated, and off we went. 20 min later we stopped and checked the 2 readings. The Polar said he had averaged 265w. The PT said 240w.

Thanks J-Law, you just reminded me of one more "question" I had about the previously cited paper. One thing to remember about the Polar computer and software is the the average power reported is WITHOUT ZEROS. In other words, any data samples where there was zero power recorded are NOT included in the average reported on the computer. The PT on the other hand, gives the average with zeros included.

So...if during your "test" there were any instances of coasting, you'd expect the power reported by the Polar to be higher than that reported by the PT. The only way to compare both PMs with equivalent averaging techniques is to import them both into cyclingpeakssoftware or else import the Polar data into Excel and perform the average with the zeros included.

If you want to compare the averages without resorting to downloading, you have to make sure your "test" doesn't contain any coasting!

Which brings me back to the comparison paper. The only thing they say about the uphill field test is that it took place on a road with an average grade of 5.3%. They don't show the actual profile. If there were any downhill sections (or even turns) where coasting occurred, the average power reported by the Polar will be higher. The paper also doesn't describe how the average power readings were determined. Were they just read out of the computers (with the possibility of the error described above) or did they download the data and calculate it themselves?

Tom

Quoted post said:

Originally posted by acoggan
I never cite a paper I haven't read.

An excellent rule to follow....I wasn't sure, since the quote you cited was from the abstract portion of the paper.

In any case, does that mean you're in complete agreement with the paper's conclusions? Or, do you think any of the reservations I've expressed have merit?

BTW, see the reply in this thread I gave to J-law about his "mini-test". One other thing I forgot to mention previously is the possiblity of the high Polar readings found in the study being a result of the Polar reporting average power without zeros. More detail about the field test and how the average powers were determined is needed to make sure this isn't a factor.

Thanks,
Tom

Quoted post said:

Originally posted by acoggan
I never cite a paper I haven't read.

I bought a 710 power meter and sent it back not fit for purpose. It was awful and Polar admitted it was no good on a trainer, where lets face it a serious athlete will do most of his controlled power work. In a 7 interval test at a constant 80 revs I got 7 different power values as far appart as 30 watts!

I bought an srm as I was serious about power work. This is constant and accurate every ride. I did though email srm who never reply, to ask how often it needs to be returned for clibration as this is critical for long term use and comparrison.

Any ideas?

Steve

while i'm just a recreational cyclist (i.e., i do not race), i take my fitness seriously. i bought the polar power meter after spending $'s on the s720i because i liked the software Polar used to track mileage, cycling & HR functions.

after buying the Cyclist's Training Bible and The Ultimate Ride, i began to be sold on using power as my source of determining my workouts & rides. the most cost effective unit that seemed to pass the "internet research" test was the Polar power unit.

i had no trouble installing it, contrary to the horror stories i'd read about. i assumed that for the price, i was hopeful i would have a +/- 5% factor of accuracy. if it is reasonably close to that range, i am satisfied with my purchase.

again, i do not race, so i can't speak from that kind of experience. but i am quite sure that even with any inherent accuracies that may exist in the unit, i am beginning to benefit from more focused training using power instead of just HR.