Fitness Test calculation

[2old2fool]

First, as a new iBike Pro v3.09 owner—my first power meter—I'm thrilled with the device and its capabilities. The iBike folks are terrific and very responsive to all my questions. Thanks!

For my first post, I just did the Fitness Test and have a question about the result. The iBike user manual shows Boyd's fitness table and states w/kg is calculated as average watts for the 20 minute ride divided by body weight in kilos. The Fitness Test gave me a 2.78 w/kg or high 3 rating.

My weight is 175 lbs. or 79.38 kilos and my average watts for the ride was 251. Thus 251 / 79.38 = 3.16 which is a low 5. A 2.78 reading seems to suggest either my watts were 220 or my weight was 90.3 kilos or almost 200 lbs. Yikes! BTW: the 200 lb. number is closest to my bike + rider weight of 203.

High 3 to low 5 is a pretty big difference. Can anyone tell me what I'm doing wrong? I've attached the ride file.

[R Mc]

What weight did you enter into the screen for the fitness test? The weight you entered for the ibike profile (your weight + bike) or your body weight?

You want your body weight for the fitness test--if you entered 200lbs wrongly, the unit will figure based on the 200, even though the 175 was right--so the 5 level would be correct.

Make sense?

[2old2fool]

I entered my body weight of 175 lbs. hence the reason for my post. I recall wondering whether I should enter 174 or 175. I went with the higher since I hadn't weighed myself for a few days. A few days earlier it was 174.2 lbs.

If I "ignore" the formula, the high 3, maybe low 4 seems about right based on how I feel about my fitness but a 5 would make me feel even better. It's just I'm a computer geek/Excel savant who dwells on the calculations and find it hard to "ignore" the formula when I have its inputs.

[racerfern]

Also note that the calculation takes the result and multiplies it by 90 or 95% to allow for the fact that you performed a 20 minute test not a 60 minute test. And don't forget to allow for drivetrain loss, I'm not sure if that is taken into account.

Here's my math for your numbers
175lb = 79.38kg
251w/79.38kg=3.16w/kg
3.16w/kg*.9=2.84

Boyd's racing in Philadelphia this weekend so we'll have to wait for him to confirm some of these numbers.

Regardless, you've set a starting point. Follow your training program and take the test in the same location in a few weeks to see your improvement.

[2old2fool]

I concur vis a vis a baseline from which to build; it's all "relative" after all isn't it?. Still, I'd like to get the deeper understanding that Boyd might provide when he returns.

Perhaps a feature request might be to specify the length of the TT, i.e., 20, 30, 40, 60 minutes and get results accordingly. Hope to hear from Boyd.

Thanks Fernando!

[coachboyd]

I'm back. . . kind of wiped out but I had time to check this out.

What happened here was your tilt was off for the first part of your fitness test. So after 5 minutes the tilt correction came into play and it corrected itself. The iBike uses a five minute view to fix the tilt whereas the software can do it instantly because it's looking at the whole picture. So when you downloaded the file, it corrected for the first five minutes and the correct watts of 251 were shown. Unfortunately in the iBike it was showing 219 watts because of the tilt being off at the start.

Did you ride before doing the fitness test and then start this file by starting a fitness test? I know that when you do a trip reset your tilt goes back to the pre-corrected tilt, but if it does it when starting a fitness test that may be something we have to look into.

[2old2fool]

Thanks so much for your reply under the circumstances. Hope you did well and being "wiped out" is worth it.

Doing a trip reset before leaving, I did ride out to my start location for the test. Arriving warmed up, I started/finished the test and rode home but I did have three ride files on the iBike when I got back with the Fitness Test as #2. Does that help? Did I do it wrong?

Your explanation helps a lot. 251w/79kg = 3.17 and the lower number on the iBike itself was due to 219w before correction by the software. I'd be neat if the software handled/recorded the test scoring too then it would've corrected the Fitness Test score as well.

On another note, I picked up the WKO+ software and the Allen/Coggan book and am chugging through it. On page 51, I found mention of the 20 minute test and the watts times .95 idea that Fernando mentioned in his post. Following this then, 251w X .95 = 238.45w. So would 238w be my FTP?

Last, in the same chapter in the discussion about determining FTP, they suggest NP would be more precise (p.45). If WKO+ determined 257w NP for the Fitness Test, would it be more precise/accurate to calc FTP as 257w X .95 = 244.15w? This didn't have a huge effect on the Coggan-calc'd Power Ranges but there was a difference. And I get the sense NP, rather than average watts, would be the best number to use in categorizing workouts in the ranges, right?

Thanks again for you help and sorry if this has strayed off the iBike path too far. I'm thrilled with the iBike Pro and your support and learning about a whole new world after relying on my HRM alone for so long.

[coachboyd]

That info does help. I'll see what we can do to make it so this is fixed in the next firmware.

The 20 minute power multiplied by .95 is a great way to check for threshold. Nobody likes to go out and do an hour long time trial to determine threshold, and even fewer people like getting their finger pricked while riding an exercise bike. So the 20 minute test works out fairly well.

In the newest firmwares, when you do a twenty minute test the iBike will automatically adjust your FTP number to your 20 minutes watts * .95. This FTP is used for calculation of TSS, NP, and IF. Of course you can manually enter any number you like in the FTP CNFG screen.

[racerfern]

And I get the sense NP, rather than average watts, would be the best number to use in categorizing workouts in the ranges, right?

If you pedal at a steady state for 20 minutes your AP will equal NP. NP just takes the hard efforts and spreads them over the lower effort times and especially over the coasting time. So for me yesterday's 60 mile ride showed AP of 144 and NP of 178.

However the hardest 20 minutes of the ride show AP=190 and NP=208. That means that I was almost constantly pedaling and constantly working hard.

If you do your best twenty minute effort and your AP doesn't almost exactly equal your NP then you didn't do your best twenty minute effort.

[2old2fool]

Wow, you guys are great. So in my Fitness test, the AP was 251 and the NP 257. Close enough to assume a good, solid effort, i.e., approx. 2% difference AP vs. NP.

Thanks.