HELP! Sprints / Anaerobic Huge Difference in Erg Mode

Hi all,

So i just started the General Build Low Volume and did the FTP test yesterday increasing by FTP by about 10 watts.

Today was day 1 - Spanish Needle. I have only really done v02/threshold/SS workouts so far - this was my first time doing micro sprints.

As you can see, i tried the first part in ERG mode and switched to resistance for the second set of intervals. I have always trained with ERG before and never used resistance.

I was really surprised by how much more i could do in resistance mode - these felt powerful and more like real riding - i felt like i was really working my repeatable sprint power.
Erg mode just felt absolute killer on lower watts.

I was averaging well over 400 for these 15 seconds, compared to around 330 with ERG. I decided to switch to ERG and just switch to resistance when i felt tired or wanted it to feel more fun. I presumed whatever felt harder was giving me the most benefits.

But then i thought - if i can push higher watts quickly on resistance mode and relax during the rest more easily, isnt this the main aim of sprint training?

What do you guys think is the best way to do these going forward? Erg mode which feels harder but i push lower watts during the peaks and dont seem to recover between sets or resistance where i can basically ignore the target and hit them much higher, and easily repeat them?

Thanks :slight_smile:

For above threshold work, resistance is always a safe bet. This especially holds true on short intervals.

With resistance mode, as you found out, you may be able to exceed the target power getting additional benefit. On the flip side, if there are intervals that its hard to hold the prescribed power, like longer VO2 max work, in resistance you can still complete the interval even if your power drops, allowing you to still get a lot of benefit.

Yeh i think i will start using resistance for V02 work as well.

ERG mode is so hard on those if my cadence drops and usually stops some sets short of what i could do if i just pulled back slightly.

Just believed ERG was always the best ‘you are forced to complete it’ type of workout

I use ERG mode in all sprint workouts, well into the 800 watt range, i.e. Charing. All seated at high cadence.

I don’t see the benefit in using resistance mode to exceed prescribed wattage via random spikes.

If you’re finishing sets with gas left in the tank, you can bump up the intensity (as stated in the workout text).

If you’re having to decrease intensity in the later sets (as you’ve done), that’s fine too, but the last thing you should be doing is trying to “overachieve” in the earlier sets.


But this is what im finding strange!

In erg mode i find it really hard to maintain the wattage

In resistance mode i find it easier to maintain a higher wattage

I know this doesnt make sense, but i have checked. In resistance mode i am not doing those peaks and dips that usually results in people finding resistance easier than ERG. I am actually maintaining higher watts in resistance mode for the whole interval…

I found that in ERG mode and riding with garmin vector peddles, the feedback from the trainer and peddles were vastly different in these situations. So where the trainer might say 350w on ERG the peddles were reading like 450w. It would take like 10-15 seconds for the trainer to settle on erg while telling me it was already at target. That’s a wahoo kickr with smoothing turned off.

Keep in mind the location that each measures power. The pedals are at the earliest source possible, the trainer is about the latest source possible. Add to that the difference in HOW they each measure power (pedals = direct force strain gauge while the trainer back-solves power via the electrical properties in the resistance unit) and you get notable differences in the refresh rate between those two devices.

Some delay for the trainer is inevitable, and it will never be as fast as the pedals, even with no smoothing applied to either one.

Could you give us a link to the ride data? If you have it in public I would love to take a look at what the NP was for your spikes in resistance mode versus the ERG mode.
I have wondered this relationship for a long time and this weekend I am dong Spanish Needle as well.

Anecdotally, this is exactly how I perceive nearly all efforts once I even start to approach threshold in erg mode. I attribute this to the trainer (Tacx Bushido - wheel on), as it feels like I’m pedaling through mud most of the time.

Historically, if it is a sub threshold workout, I’ll leave it in erg mode. Otherwise I tend to put it in resistance mode because it feels more like riding a bike and I can actually do the workouts. As time has gone on, I’ve just used resistance mode more and more.

When in doubt, trust your RPE. That is, higher, easier watts could very well be “fake watts”. Great for Zwift, bad for everything else.

Others have already mentioned some possible reasons for power misreadings. Another possibility is flywheel speed differences when in each mode.

Interesting. I was gonna say, pick whichever mode makes it easiest to complete the workout correctly (not just “hit thepower targets”), but i didn’t realize that for some trainers, different modes could actually read watts differently. strange.

Can you access it? Not sure how to make it public

You can see the higher watts when i switched to resistance. Those ones in ERG felt horrible so i had to lower the resistance by 5% towards the end - and had to switch to resistance mode in the penultimate set (again i hit high watts here which doesn’t make sense)

But yeh those erg watts really felt higher than what was on the screen.

Im on a kickr snap btw. I’ve known that watts shown was lower than how it actually felt, but now im thinking its more to do with ERG mode…


It is a private Ride. You would need to go into “Account” and change the account from PRIVATE to PUBLIC. If you dont mind that, then I can see the data.

I am also in a Kicker SNAP and have also noticed the issue with sprints or quick hard efforts. My feeling was that it had to do with my power meter and the kickr trying to match it.

I wrote another thread about my annoyance with the seemingly inaccurate kickr snap.

Im tempted to get a power metre that i can use to power match and remove my uncertainty (plus use outside when we are allowed out) or upgrade to a direct drive.

I’ve made it public now

Last time I did micro sprints I left it in erg and it felt pretty easy with it only taking a couple of seconds to level out (tacx flux 2 with powermatch Garmin vector pedals). Use big ring, middle of the block.

The times I have tried resistance mode I’ve needed to be in one of the lowest gears for rest intervals and highest for the effort. Been a ball ache changing so many gears to achieve target.

Am I the only one with this experience?

That’s odd, I always find erg mode easier than resistance or riding outside. I feel like for hard intervals, erg mode always enable me to put out right enough power to meet the target, but if I ride resistance or outside, my power fluctuates more, and in the end, the power spikes cost me too much energy and I can’t meet the power target for the following intervals.

1 Like