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 Post subject: FTP test on hometrainer
PostPosted: Mon Dec 05, 2011 12:05 pm 
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Location: Denmark
Last year I trained on a Tacx Bushido during the winterseason, and used the watt feature a lot. I did a 20 minute test to determine FTP, and took 5% off that number to get an estimate of FTP. The figure was 240 watts, so it equaled to 228 watts.

This season I have a P2M powermeter and have bought an Elite Supercrono Powerfluid trainer to do my intervals. Yesterday I did a test again, although with a bit different setup. 10 minute warmup, 5 minute at "FTP"(230 watts), 10 minute easy rolling, and then the 20 minute test. This gave me 224 watts, which equals to 213 watts FTP.

In late October I did a 20 minute test as well, on the road. Which gave me an average reading of 253 watts, which is 240 watts FTP.

So, now for the questions.

1. What could be the reasons for the different numbers when comparing road and turbotrainer? My guess is that the trainer is a constant wattage, whereas the road testing gives time for small breaks, changes in cadance etc, as well as the fact that body temperature will be lower out on the road compared to a room.

2. Tacx vs. P2M numbers. My guess is that the Tacx gives out a higher figure than the P2M. I read somewhere that the Tacx is 20-40 watts off compared to a Powertap. True, false?

In the road test I kept a cadance of 99 RPM, whereas the Elite session was 108 RPM. Should this affect my numbers?

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PostPosted: Mon Dec 05, 2011 12:30 pm 
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I use a tacx fortius which allows calibration. If done it was within a few watts of the SRM. Tyre pressure can effect power readings. And the biggie - thermal stress of outdoor vs indoor (even with a fan). There can also be psychological factors too.

Your differing cadence should not make a difference.

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Posted: Mon Dec 05, 2011 12:30 pm 


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PostPosted: Mon Dec 05, 2011 1:04 pm 
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I had an Elite Supercrono Fluid trainer and found it really hard to match my road Wattage. Now have a Cycleops Fluid 2 which is way more enjoyable to ride and turbo and road Wattage are much closer. I think the resistance provided by the Elite turbo is really unrealistic and the clamping system on the Elite trainers makes it hard to ride at a nice smooth power output since if you move around in the saddle even a little the resistance changes a lot.


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PostPosted: Mon Dec 05, 2011 1:33 pm 
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Well, I don't know how you have trained since your last test, but this saturday I did a 20 min medium interval, or what used to be medium interval, on my hometrainer and the average was 246 watt. In the end it was harder and my hearrate was clearly higher than it should for a medium interval. In the and of september I tested my ftp with a 20 min interval, like you, and calculated my ftp to be 289 watt. Right now I think my ftp is somewhere near 260-270 watt.

And why? Lack of form! Hope to raise my ftp to over 300 watt when the season starts in april.

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PostPosted: Mon Dec 05, 2011 3:10 pm 
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Location: SC, USA
Keep in mind that FTP testing is only a snap shot of your fitness. It is good that if you train in cycles to test at similar points. Your threshold can obvious change depending on recovery/freshness/etc.

Also, the biggest problem that I have seen for some folks in getting accurate FTP measurements is in thermal consistency. Get the biggest fan(s) you can buy, and keep your HVAC system running cool. You're going to want to be on the cool side when you start. Tempature of the room can have a major impact in prolonged threshold intervals. Basements are great!

I'm becoming more a believer of out door tests for accuracy. But not everyone has access to perfect weather year round! I like indoor tests because they can provide a motivational target. When you are doing your intervals, you can say "I'm 110% of my 20min CP"... or whatever. That sort of thinking is always good, and keep you coming back for more.

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PostPosted: Tue Dec 06, 2011 2:49 pm 
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For me, power is always much higher outdoors; even though I have multple fans and windtrain in a very cool basement. There is just something about fresh air and changing scenery. Indoor training is simply too mind-numbingly boring.

Indoor seems good for setting a sub-ftp target and trying to hold it for a certain period very steadily. But I just can't keep up the motivation to "hurt" very much or for very long indoors.


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PostPosted: Tue Dec 06, 2011 5:37 pm 
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The lower power or boredom riding indoors has nothing to do with lack of fresh air or scenery.


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PostPosted: Mon Dec 12, 2011 1:33 pm 
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Location: Australia
Appologies for the hijack but this may be relevant if you will be training consistently indoors as well as outdoors.

Is it possible to have an indoor and outdoor ftp?

For example, if you train 50% indoors and 50% outdoors and your testing indoors is consistently lower than when testing outdoors would you use indoor numbers for indoor workouts even though they are below your actual FTP? And conversley use your outdoor numbers for outdoor training?

Also, for those that must train indoors during winter, do you test indoors and use these numbers even though you know they are most likley lower than your best effort?

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PostPosted: Mon Dec 12, 2011 1:40 pm 
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I would use an indoor/outdoor ftp. You are right, most people will see higher watts on the road.

I am training indoors all winter and I use an indoors ftp test to set my zones up.


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PostPosted: Tue Dec 13, 2011 5:48 am 
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What is said above is very true. For most people (there are exceptions) they have an indoor FTP and one for outdoors. As far as why this occurs, everyone has a theory - but in general most people tend to see about a 5-8% power drop from riding the trainer to riding outside.

Cadence will not affect numbers assuming you are using a cadence that is of your personal preference. I know that I cannot hold 90% of my FTP for very long if I am spinning at 130rpm.

As far as Tacx numbers vs. other power meters, I would suggest paying more attention to your everyday power meter as that is what you will be using 100% of the time - indoors or out. My experience in the past has been that Computrainers (even lab ones) (and possibly Tacx trainers) generally differ in wattage by 10-30w. I remember going in for a Vo2 max test that they hooked my bike up to a lab grade computrainer. My powertap showed consistent wattage that was 30w lower than what the computrainer was showing. My friend who went through the same test had his powertap show a 15w discrepancy.


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PostPosted: Tue Dec 13, 2011 4:32 pm 
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Location: Exeter, Devon
The problem, or should I say key to testing is maintaining consistency. This includes measurement tools, Tyre pressures, room temperature, cooling etc.

We encourage all our guys to come for their pre-season testing, and subsequent follow ups through the year. We can guarantee the same testing conditions, motivational abuse/encouragement etc etc. All this will provide an accurate measurement of 20min threshold in those specific consitions.

As mentioned, the difference between on road and indoor results differ between different people, however we work hard to minimise any thermal effect of testing indoors.

Our protocol is outlined here http://www.koolstofcoaching.com/articles/training/how-fitness-tests-improve-race-results

As for Tacx trainers and wattage. we like the Tacx machines, but the wattage they show is only accurate to themselves.

And a final point, when measuring power with a powertap, you will always get skewed results compared to those given by a Computrainer. This apparently has to do with the hub being clasped, and it somehow effecting torque readings. Way above my technical knowledge. We have done some tests and the difference seems to be greatest (roughly 20-30 watts discrepency) at mid range watts (220-280watts) and then the discrepency lessons as wattages go over 300.

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PostPosted: Tue Dec 13, 2011 6:09 pm 
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Ghost234 wrote:
What is said above is very true. For most people (there are exceptions) they have an indoor FTP and one for outdoors. As far as why this occurs, everyone has a theory - but in general most people tend to see about a 5-8% power drop from riding the trainer to riding outside.


I don't know why people still treat this as some big mystery. The cause of lower power indoors (other than the obvious need for cooling) has been known for a long time. Not only has the problem been identified but it has been solved.


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PostPosted: Tue Dec 13, 2011 11:44 pm 
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Please explain?

Micro breaks? Low inertia? Different pedal force application?


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PostPosted: Wed Dec 14, 2011 4:32 pm 
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koolstof wrote:


wait "A test uphill will always give a higher power output than the flat and power to weight ratios will make the test less accurate."

why is this? if u are able to do lets say 300 watts for 1 hour going up hill why is that less accurate than being able to do 300 watts for 1 hour on a flat? (if i'm reading into it correctly?)


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Posted: Wed Dec 14, 2011 4:32 pm 


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PostPosted: Wed Dec 14, 2011 4:50 pm 
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Quote:
"A test uphill will always give a higher power output than the flat and power to weight ratios will make the test less accurate."

I don't believe it is "less accurate". Only "different" because of the different mechanical impedance on a hill vs on the flats.

Just like car engines reach maximum horsepower, maximum torque, and maximum efficiency at different RPMs, so too do human "engines".


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