Fluid trainer linearity v. time

[886014]

I have just installed a Polar Power sensor as my first introduction to power training and am just trying to get used to the idiosyncrasies of the unit.

I have a Travel Trac Century Fluid trainer and today tried some intervals. After a 10 minute warm-up at around 180W I did 8 intervals at a constant speed and cadence for each interval. I noticed the power indicated dropped for the first 4 intervals, then seemed to stabilise for the next 4 intervals.

I was wondering if the fluid trainer tends to provide less resistance as the fluid gets hotter with each interval (up until a point) or whether I have a lot more to learn about using the Polar?

Cheers

 

[frenchyge]

I was wondering if the fluid trainer tends to provide less resistance as the fluid gets hotter with each interval (up until a point) or whether I have a lot more to learn about using the Polar?

The resistance will decrease as the temperature rises. My trainer boasts the "lowest operating temperature in the industry" and I see about a 2.5% drop in power (well, really a 2.5% increase in speed to maintain power constant) over a set of 6 VO2max intervals (after a 10min warmup).

I also seem to recall seeing occasional comments about Polar power readings in high gears or on trainers, so there may be something there as well.

 

[886014]

Thanks. BTW the indicated speed and cadence (from my computer) were held constant and the same gear used for each interval ie precisely the same bike configuration. I'm presuming the viscosity of the fluid is decreasing with increased temperature hence providing less resistance(?)

 

[frenchyge]

Right. As the temperature rises, the viscosity of the fluid decreases and you'll see a drop in power during your constant speed intervals. I ride constant power intervals, so I notice the same thing causing an increase in speed for me.