22nd March Powertap v Lifefitness Comparison - the test

Day off today so carried out the comparison test I have been planning since getting the Powertap. Most of my power measures to date have been on my Lifefitness exercise bike so interested to see how that compares in terms of watts to the "real" thing.

Premise was that I could use heart rate as a measure, the correalation between it and power on Powertap/Lifecycle should give a measure of how similar when displaying watts.

Decided to carry out test as follows:

• Do 4 sessions each 30 minutes long. Sessions 1 and 4 done on Powertap, 2 and 3 on Lifecycle.



• Target watts for each session is 100W for 10 minutes then 4*3 minutes ramps increasing to 140W, then 180W, then 220W, finally 260W (so up to 22 minutes) then back to 100W for 8 minutes. Pedal at a cadence of 80-85 rpm throughout until the last 8 minutes which would be at 70-75 rpm.



• Logic behind these values is that I know I can do these comfortably so will not tire during the 2 hours the test takes. (Also eat a small 150-200 cal snack at the end of each session to keep topped up. ) These power values are also where most training is carried out. Having the long run in/out of 100W should give enough time for my heart rate to return to normal between sessions and also provides a good base value.

Session 1 Powertap. First session on Powertap was interesting. It took a while to get the cadence/gear right so that the power was in the 100W average. Again each ramp up took a while to get used to in terms of target watts. This can be seen in the power graph below where within each stage of the test the actual power can be seen to be varying quite a lot around the average, with a noticable spike up at each ramp up.

In the end though managed fairly well to make the actual power hit target. Actual averages were 98W, 138W, 178W, 219W, 261W and 103W. As expected at the end of the session I was not feeling at all tired. One good thing about having to concentrate on the average watts measure was that I had not much idea what my HR had been. So I would do the Lifefitness tests blind in terms of expectations of HR on the Powertap. Had a Twix at the end of this session.

Sessions 2/3. These were a lot easier in terms of carrying out the test as it was just a question of choosing the "Watts" program and setting the same watts as done on the Powertap. Subjectively the sessions felt similar in effort to the Powertap and again at the end of them felt not at all tired. Had a break between the two, having a banana and cereal after session 2 then some chocolate (not planned but my son had some on offer) after session 3.

Session 4. The second session on the Powertap and the hardest in terms of hitting the desired watts target. This was partly my own fault as I wanted to try to make a note of the gears I was using so a number of the ramps show sudden dips as I look down to check the gear being used.

Anyway finally finished. Followed up with some roller work (see other posts)