Use single leg drills to assess L/R imbalance for single-sided PM?

Forgive me if this has been covered previously, but I can’t find it in a search…

So I’ve just bought a 4iiii left crank PM and I want to do an assessment of my L/R leg power balance so that I can set the appropriate % balance in the 4iiii app. The probem is, I don’t have access to a Wattbike or other dual-sided measuring device.

I wondered what value there may be in doing some single leg drills to get a feel for the potential output of my left and right. I realise that it won’t be exactly scientific (and I also know that some peoples’ imbalance switches depending on level of power and fatigue) but thought it might be worth doing as a rudimentary test. As in, better than nothing.

I also realise that it’s the consistency that’s important rather than the absolute figure (so you could argue that it doesn’t actually matter), but I can’t help wanting to be displaying something approximating my actual both-legs power when my left leg power is simply multiplied by two.

Maybe it’s just my fragile ego…just kidding, I’m genuinely interested in finding out if this is a possible method.

Comments appreciated!

I can’t see that working at all with any accuracy. There are enough physical changes from the act of unclipping and pedaling with one leg in place, that it is not really comparable to both legs clipped in and working in succession.

Not sure it is any better than making a guess… or just ignoring it and accept what you get from the simple 50/50 assumption. Unless you get access to something with real L/R, I don’t think it’s practical to back-figure anything worthwhile.


Single leg drills won’t give you squat unless you have an “accurate” trainer/dual sided PM to compare to. Simply pedalling as hard as you can with your left leg won’t give you the data needed for a useful offset adjustment.

For the record, I own 2x single sided PM’s. One Stages G3 and a 4iiii Precision. I’ve managed to balance everything pretty closely with my Neo2 by dual recording loads of different outputs in varying states of fatigue. Single leg drills are the only way to determine if the trainer and PM agree to begin with in this case.

I did have a chuckle when reading a thread a few weeks back where the guy was trying to blame TR ILT’s for an injury. I’ve done so many of the bloody things on my left side only I was worried I was creating an imbalance. I think my longest one was over 6.5 mins.:sweat_smile:

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Thanks guys.
A bit more clarity from me would help…

When I said do some ILTs, I meant on the Kickr Snap, independent of the power meter, and without the power meter even being on the turbo bike.

Just sort of like a maximal power experiment for the right leg, then the same test for the left.

If I did it in ERG mode I could make it like a single leg ramp test, then do a quick ratio calculation of the maximum wattage I could pedal, to failure, with each leg, independently.

If you’ve got the Snap set up well you should be getting fairly consistent results at least.

You could dual record like I mentioned and get a pretty good idea of what’s going on. If you go down the path of trying to do a ramp test on each leg you’ll probably end up regretting it.
Don’t hurt yourself.

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  • OK, but you made no mention of any other power device used in the OP.

Despite having what amounts to a total power device in the Snap, I still think the general differences in pedaling single leg clipped vs both clipped will give far more variability than you can expect to convert to a “normal” leg power split.

  • And as you also mention above, people’s L/R splits tend to vary along the power range. Focusing on a “max” effort may well be worthless at lower power levels. Some people are consistent across the range while others vary.

I see it as a lot of effort for little payback in even the best case. Consider that the data would likely be very questionable, I just don’t see the benefit. :man_shrugging:

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Thanks again for your comments, guys. I guessed it was probably a crazy idea. I have a good friend with a Wattbike but due to lockdown restrictions I’m not allowed to go to her house! It will just have to wait.

It’s not important, it’s just another pleasant little distraction from the reality of Covid-19 over here in Scotland!

Good luck to you with your training and with your election!

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You shouldn’t need the Wattbike to get a rough guide. You already have a Snap which is good enough IME.

Set yourself up to dual record and run a few tests. You should get enough to play with the 4iiii settings from your kit.

Try this:

  • Warm up/Calibrate/Zero/Update/Inflate/Lubricate everything involved.
  • Build your own TR workout that will allow you to hold various powers for periods of a minute or more if possible. Make it a range from low to high wattage’s that you can hold with on leg.
  • Complete the workout with only your left leg clipped in and review each section to see how it aligns with the Snap after you divide the number by 2. (My Core was out by >20w vs the Neo2 and 3 different PM’s so don’t be shocked if they don’t align).
  • Now do the same workout with both legs and compare the difference for a rough guide to your imbalance.
  • The more you do, the clearer the picture will be.

In my case I have dozens of data sets with various devices and even though I’m using L only PM’s I’ve been able to get everything lined up pretty well now. YMMV, but I’m able to use all of my bikes and not worry about adjusting for indoor vs outdoor workouts anymore. FTP estimates are all within 6-7 watts currently and power PR’s all line up pretty well also.
If that’s your goal, it should be doable with the equipment you have on hand.


I love step 1! :joy:

Seriously, thanks for the tips, much appreciated!

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