Different smart trainers & change in effort...."Inertia"

Hi All, Im not new to indoor training and using a smart trainer, however…
Ive been using a Wattbike atom the last year or so. I was on a mag dumb trainer before, and I when started using it I noticed that my cadence increased. After a few weeks of monitoring this natural change, I began to wonder why this was.
I thought it was great as like many, I was/am a bit of a grinder. I had previously tried to consciously increase my cadence but with no noticeable sustainable change.
Eventually in any session where I hit a certain level of fatigue the cadence begins to drop and any effort to sustain a higher leg speed exerted more effort than just riding at my natural cadence.

So over a year later cadence is still higher on the wattbike and does seem provide less fatigue on the legs with the lower torque. I find it easier managing the slight increase cardio effort with the higher cadence.
I’ve also noticed I’ve never seen any posts or articles about smart trainers having this effect in general. So I recently moved over to a CycleOps H3. I’ve done a hand full of sessions and the feeling of being able to spin my legs quicker is gone.
My power numbers on the H3 have dropped as HR and PE are higher if I try sustaining my “WattBike” numbers.
I have not played with the gear settings on the bike on the H3 yet but this clearly feels like something related to inertia.
The only way I can describe it is, on the H3 I feel like I’m constantly climbing vs doing the same effort on a flat on the Wattbike. I think most recreational cyclists can relate to how much harder a climb feels at a threshold effort vs riding on the flat. (I know this might be a generalization, so excluding the natural climbers vs. TTists here)

I would really like to understand the biomechanical effect on this topic…
The topic/question being.
Why exactly is it harder climbing than on flats? The general textbook answer is higher inertia, but what does that mean?
I logically understand to a point, on a climb the pressure on the pedal is more constant all the way through the revolution of the crank. On the flat the effect is more like being on a spin bike. You are pushing the same power value but there is some contribution from wheel in certain parts of the crank revolution. (at least that’s how it feels)

So here is where I would love to get a better understanding (or be corrected). If anyone is qualified to answer I would really appreciate it.

Points to note…
Ive been on multiple Wattbike Atoms all with the same result (high cadence) so dont think this is a power discrepancy issue
Its a new H3 and the numbers match the numbers on the quarq PM on the bike so its accurate.
Over the past year I was not sure if the higher cadence was translating to the road. I certainly was putting in more thought into riding at a higher cadence, but its too subjective to be sure.
Ive tested this on a few indoor cycle training apps, all with the same effect. Again not playing with settings on the Wattbike of gearing when on the H3.
My training on the H3 has all been in small chain ring and easier gears. (Yes I will try in big chain ring to see if the higher intertia related to higher cadence)

thanks all

This is the important detail. The standard recommendation is to use the small chainring on a 2x drivetrain and a gear in the middle of the cassette. I would suggest playing with the gearing toward the middle and see how that feels.

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There was an old CyclingTips article referenced many times before. Sadly, it seems lost in the web or locked behind Velo’s paywall. But the related discussions that referenced it may well be worthwhile:

sorry I should have mentioned that I have it in the middle of the cassette.

thank you

I split the statements above since it is important.

  • You may have a match between the H3 & Quarq so they align, but there is a larger question.

  • Unless you run a similar test between the Atom and power meter pedals, on the bike with the H3 (and Quarq), there is no guarantee that the Atom & your H3/Quarq “match”.

  • We’ve seen many cases where devices do NOT align, so it’s a mistake to think your power data on the Atom would match the H3/Quarq. It might, but I wouldn’t just assume so without testing to confirm.

That means that “power data” and FTP info derived from your prior experience on the Atom may not be comparable to the H3/Quarq.

  • This is one reason for the common suggestion to retest anytime you change a large element in the power data chain. The actual power data device is one factor and an important one.

  • But the trainer / smart bike also includes the inertia aspects is also important. Even if you use the same exact power data device (like power meter pedals) between a change like this, the inertia delta may well alter the RPE and ultimate power test results.

First and foremost, I would recommend an FTP test on the new setup to rule out any potential influences.

  • In tandem with that, you should consider the inertia (gearing) you plan to use. Testing with whatever you intend to use in training is best practice, IMO.
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@Nicstuber First, you are trying to make sense of multiple artificial cycling environments. I’m not sure it’s possible.

200 watts, for example, will feel different in big gear versus a small gear because the flywheel will be spinning faster in the big gear. Personally, I do most steady state and easy zone 2 training in my small chainring and high power intervals and threshold tests in the big chainring.

Personally, I think holding threshold power on an incline seems easier to me than doing that on the flats.

You probably aren’t going to have two trainers that agree on power. You need to retest your FTP on the new setup.

Thanks all for the feedback. All food for thought.
I knew posting this without actually testing the gearing on the H3 and other variables would leave too many questions unanswered.
I know many have referred back to probable power discrepancies between the trainers (which could be contributing) but the slowed cadence is really got me interested.
Regardless will let you know after a few more sessions in different gearing.

12ft Ladder will solve it

Gosh, if only somebody had figured out a way to deconstruct Garmin’s “Pedaling Dynamics” metrics to provide better insight into how things like inertial load influence physiological demands/responses. :wink:

Serious answer: motor unit recruitment depends not only on the force requirement, but also on the velocity of the (intended) movement. My theory is that a given power feels/is easiest when the “loading conditions” most closely match the contractile properties of the pedaling muscles, and becomes progressively harder as you move away from this optimum. While this is almost certainly trainable to some extent, it likely also depends on factors like muscle fiber type distribution, etc.

TL,DR: Don’t race me on a 4-6% grade, or on a Lemond trainer, as that’s right in my sweetspot.

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Yes, because stealing copyrighted content is something to be encouraged.