inconsistent power from ride to ride

[cbuchan]

I thought I had this figured but today I went out to do my first threshold intervals with the power meter and numbers out to lunch.
Wednesday May 6th did a FTP test on the road with the power pod. Friday recovery ride everything looked in order. Today tried to do a threshold interval session and the harder I worked the lower the power number!!!

Same bike, Same mount, Same road.

[Velocomp]

This is a very interesting set of 3 ride files, and thank you for providing detailed descriptions of each so that I could interpret them properly.

The big puzzle is between your 5/6 ride, where you set your threshold power, and your 5/9 file, where you get significantly lower results.

I analyzed the threshold stretch on 5/6, and the comparable section of your 5/9 ride

I see the following:

1) Your PP looks to be properly calibrated. I say this because wind speed and slope readings are within range

2) Wind strength and direction varies considerably between these rides

3) On your 5/6 ride you had a slight headwind in the threshold interval. An aero coach analysis shows that PP measured 234 watts is very close to calculated 233 watts

Screen Shot 2020-05-09 at 5.45.51 PM.png (185.92 KiB) Viewed 3893 times

On the 5/9 ride you had a pretty significant tail wind in the same section. Also, your bike speed was lower. You were not working as hard...

Screen Shot 2020-05-09 at 5.43.42 PM.png (194.19 KiB) Viewed 3893 times

PP measured 163W; aero coach calculates 162W

In both cases, calculated and actual watts are extremely close!

The power data suggests that you did not work as hard on the 5/9 ride, and the sensor data (wind, slope and speed) support this conclusion.

The only anomaly I see is your HR reading--on the 5/9 ride your HR is higher, even though you aren't putting out as many watts. HOWEVER, the temperature on the two rides is considerably different; on your 5/9 ride it was a cold 7C, vs. a nice 18C on your 5/6 ride. Whether or not temperature accounts for the HR difference I do not know.

Be very mindful that how hard you work is going to be heavily influenced by how hard the wind is blowing.

I think your PP is properly calibrated, so I would do another ride without changing anything.

[cbuchan]

Thanks, The only problem I have is that during the 5/9 ride the intervals were gut wrenchingly difficult and the power was well below 200w yet in other parts of the same ride in the hills I hit 200 and the RPE was considerably lower. The heart rate numbers on the 5/9 ride indicate this as my max HR is 175. I guess the cold could have made my breathing feel much harder.

I went for an endurance ride yesterday and the numbers seemed very consistent. I am new to using a power meter and after doing some reading from the power meter handbook have adjusted my power training zones. I will be doing some VO2 and Sub Threshold intervals this week and we'll see how it goes.

[Velocomp]

I did the ride comparison for the same stretch of road.

Compared to your 5/6 ride where you were riding at 32.6kph with a slight head wind, your 5/9 ride shows that you were traveling at a slower bike speed of 31.8 kph, with a significant tail wind.

It makes complete sense that your 5/9 ride shows lower power expended.