FTP calculation on gym bike
Discussion
I don't own a power meter, but still wanted to calculate my FTP.
So I did a 20min test on a LifeFitness GX gym bike that displays calories.
I then turned calories into Joules, then assumed 25% body efficiency, multiplied by 0.95% to give my FTP (1 hour effort). Lastly divided by my weight to give power / kilo.
Can this method be compared to others with power meters on road bikes, either outdoors or on rollers?
I guess I'm asking, how accurate are calories on a LifeFitness gym bike?
Cheers.
So I did a 20min test on a LifeFitness GX gym bike that displays calories.
I then turned calories into Joules, then assumed 25% body efficiency, multiplied by 0.95% to give my FTP (1 hour effort). Lastly divided by my weight to give power / kilo.
Can this method be compared to others with power meters on road bikes, either outdoors or on rollers?
I guess I'm asking, how accurate are calories on a LifeFitness gym bike?
Cheers.
wemorgan said:
From what I've read it seems to be a standard test to measure performance. So I was going to measure my performance and if possible to then compare to others. Just a way of motivating myself to train more.
I would just make a 20km loop on Strava (or whatever) and then time yourself and compare efforts.wemorgan said:
I don't own a power meter, but still wanted to calculate my FTP.
So I did a 20min test on a LifeFitness GX gym bike that displays calories.
I then turned calories into Joules, then assumed 25% body efficiency, multiplied by 0.95% to give my FTP (1 hour effort). Lastly divided by my weight to give power / kilo.
Can this method be compared to others with power meters on road bikes, either outdoors or on rollers?
I guess I'm asking, how accurate are calories on a LifeFitness gym bike?
Cheers.
As above, that will produce a number but it'll be so inaccurate as to make it meaningless. If the 'calorie' estimation is accurate (unlikely) and repeatable then of course you could just measure your performance gains against this arbitrary proxy measure of power, but without knowing how consistent the readings are from one session to the next you wouldn't be able to discern genuine improvement (or decline) from measurement error.So I did a 20min test on a LifeFitness GX gym bike that displays calories.
I then turned calories into Joules, then assumed 25% body efficiency, multiplied by 0.95% to give my FTP (1 hour effort). Lastly divided by my weight to give power / kilo.
Can this method be compared to others with power meters on road bikes, either outdoors or on rollers?
I guess I'm asking, how accurate are calories on a LifeFitness gym bike?
Cheers.
As suggested, pick a long segment on Strava (preferably a 10+ minute climb of say 8%+ to prevent drafting on chain gangs) and compare your times with others - if done under normal weather conditions it'll be reasonably representative of your ability against others and will also allow you to measure you own performance gains.
Out of interest what FTP and FTP/kg did your calculation come up with?
Cheers for the advice it makes sense.
How do you search for local Strava segments?
The values were: 1400 calorie hours, 380 watts or 5.1 watt/kg. Which is on the high side i admit, maybe 20% high.
On the same bike I can can also average 37kph over a 1 hour effort. Which makes me feel the bike reads high as I'm some way off that when outdoors with wind and gradients against me.
How do you search for local Strava segments?
The values were: 1400 calorie hours, 380 watts or 5.1 watt/kg. Which is on the high side i admit, maybe 20% high.
On the same bike I can can also average 37kph over a 1 hour effort. Which makes me feel the bike reads high as I'm some way off that when outdoors with wind and gradients against me.
Edited by wemorgan on Monday 21st December 21:37
wemorgan said:
Cheers for the advice it makes sense.
How do you search for local Strava segments?
The values were: 1400 calorie hours, 380 watts or 5.1 watt/kg. Which is on the high side i admit, maybe 20% high.
On the same bike I can can also average 37kph over a 1 hour effort. Which makes me feel the bike reads high as I'm some way off that when outdoors with wind and gradients against me.
'Segment Explore' in the main menu. That FTP would put you in the Elite/Pro category, so is almost certainly way too high. 300W and 4 W/kg would be roughly Cat2/3 for reference.How do you search for local Strava segments?
The values were: 1400 calorie hours, 380 watts or 5.1 watt/kg. Which is on the high side i admit, maybe 20% high.
On the same bike I can can also average 37kph over a 1 hour effort. Which makes me feel the bike reads high as I'm some way off that when outdoors with wind and gradients against me.
Edited by wemorgan on Monday 21st December 21:37
nammynake said:
'Segment Explore' in the main menu. That FTP would put you in the Elite/Pro category, so is almost certainly way too high. 300W and 4 W/kg would be roughly Cat2/3 for reference.
Cheers. Conveniently there's a 20km segment not too far from me. I'll try that in the New Year.Looking at some shorter (~5km) segments that I've done, I'm on average in the middle of the pack, which feels more accurate than my predicted FTP.
If you want a rough idea of the watts you're putting out for those segments, look for riders near you who have a 'lightning' symbol next to the power level. Those are riders who have used power meters so you can get an idea of the kind of output needed to do those times.
Caveat: There are some factors which can skew these figures a fair bit. You can see above that the slower chap actually put out more watts, so what makes the difference?
a) Weight - a heavier rider will be putting out more power
b) Wind - riding into a wind will make a big difference
c) Group riding - Say, 20% less effort in the pack vs. a single/front rider in the same conditions?
d) Meter accuracy - Figure on at least 5-10% variance between devices
If you have Strava Premium you can filter by weight to get a slightly more representative selection of riders who are close to your weight. Similarly, if you ride a busy-ish segment then you can filter for 'today only' to see riders using meters who have faced similar conditions, perhaps reducing the wind variance.
It's only a guide, but pick a busy segment and you should be able to get a rough idea by averaging out the numbers.
Caveat: There are some factors which can skew these figures a fair bit. You can see above that the slower chap actually put out more watts, so what makes the difference?
a) Weight - a heavier rider will be putting out more power
b) Wind - riding into a wind will make a big difference
c) Group riding - Say, 20% less effort in the pack vs. a single/front rider in the same conditions?
d) Meter accuracy - Figure on at least 5-10% variance between devices
If you have Strava Premium you can filter by weight to get a slightly more representative selection of riders who are close to your weight. Similarly, if you ride a busy-ish segment then you can filter for 'today only' to see riders using meters who have faced similar conditions, perhaps reducing the wind variance.
It's only a guide, but pick a busy segment and you should be able to get a rough idea by averaging out the numbers.
Edited by loudlashadjuster on Wednesday 23 December 09:44
nammynake said:
'Segment Explore' in the main menu. That FTP would put you in the Elite/Pro category, so is almost certainly way too high. 300W and 4 W/kg would be roughly Cat2/3 for reference.
That might be a little on the optimistic side - although my experience is more MTB than road. Road racing is more about absolute FTP and max power, rather than w/kg - in the UK at least.FTP of 5w/kg or above and you would be in the pack of an elite MTB race. Nearer 6 and you will be at the sharp end. A figure around 4, I would say thats Sport category.
matt-ITR said:
That might be a little on the optimistic side - although my experience is more MTB than road. Road racing is more about absolute FTP and max power, rather than w/kg - in the UK at least.
FTP of 5w/kg or above and you would be in the pack of an elite MTB race. Nearer 6 and you will be at the sharp end. A figure around 4, I would say thats Sport category.
6 W/kg FTP (i.e. for an hour) would surely be top pro GC riders?FTP of 5w/kg or above and you would be in the pack of an elite MTB race. Nearer 6 and you will be at the sharp end. A figure around 4, I would say thats Sport category.
Also look at someone like Magnus Backstedt I would very much doubt his FTP when even when he won Paris Roubaix was much over/if even over 5.5 w/kg.
Surely MTB XC is less about having a massive FTP like world tour climbers (though I'm sure it helps) but doing more intense shorter durations of power and being able to recover and do them again and again ? (though having never race MTB XC I am only guessing).
Surely MTB XC is less about having a massive FTP like world tour climbers (though I'm sure it helps) but doing more intense shorter durations of power and being able to recover and do them again and again ? (though having never race MTB XC I am only guessing).
okgo said:
You are now seeing why w/kg is generally pretty meaningless unless you're into long mountain stage races or hill climbs.
My FTP is about the same as that but I'm probably 78kg when racing, I can't think of many instances where I wish I was 60kg with the same w/kg
Alpe d'Huez! My FTP is about the same as that but I'm probably 78kg when racing, I can't think of many instances where I wish I was 60kg with the same w/kg
Actually, any alpine climb.I think I'd say the opposite, but then I love climbing and hate TT'ing - probably because of my build and the same goes for you.
If you were 60kg, then you might say different. If I was 78kg, I would probably enjoy TT'ing more.
One thing that does suck about being lighter (for the same FTP) is that bike weights are generally the same, so % wise have a bigger impact.
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