Left/Right Pedal Balance

I’ve been using my new PowerTap P1 pedals for a month now on the trainer. I usually see a 53/47 L/R wattage balance when I review a ride afterwards.  That ratio seems to hold pretty much during all types of intervals: warm-up, short VO2 work, longer FTPs, and steady state. The pedals work fine measuring left only and right only when I do single leg drills. So now I’m left with pondering (a) why the imbalance and (b) what – if anything- to do about it.

At first, I made the simplistic assumption: “Well, my left leg is stronger than my right.” But this seemed at odds with a few other facts:

  • When doing single leg knee bends, my right seems both more stable and stronger
  • When skiing, it is easier to make left turns (which utilize the right leg to the greater extent) than right turns.
  • I currently am re-habbing a left hamstring and piriformis situation.

So I dug into, and learned a bit about pedaling balance. The biggest problem people seem to have is that one leg gets in the way of the other. Meaning: if I am not sufficiently “unweighting” my foot during the pedal upstroke (6-to-12 o’clock), then the opposite (contralateral) leg will have to work harder during its 12-to-6 portion. So: if my right leg is floating up while my left is pushing down, the left will have to work harder to maintain cadence, causing the imbalance noted above.

Next step: see if this theory is correct. First off, when doing single leg drills, it does feel as if I “chain-slip” sooner and more often on the right than the left. That is, after about 15-20 seconds of a right-only drill, there starts to be a slack in the pedaling between about 10 and 12, sufficient to cause an audible sound of the chainring losing, then re-gaining its grip on the chain. Next, I discovered that PowerTap has an App which shows, in real time, a graphic representation of watts applied at the various reporting stations around the clock on each pedal. (When I used a CompuTrainer from 2007-2014, I had access to a similar metric, but never paid it any attention – just too hard to use, for me.)

So I fired that up, which entailed the usual futzing around with getting sensors linked to the app, and then figuring out just how the app worked – as usual, no user’s manual, and little online help. After a good 30 minutes of easy spinning at 60-70% of FTP, I turned to the graphs which show real time force being applied at each of the 15 or so points around the full circle of a pedal stroke. The app has three different visual representations: tangential lines coming out of the circle at each point where its receiving data, the length of which represents the wattage at that point; a color coded circle, with blue being lightest, and red being strongest, also a thin blue line when no force is being applied; and a warp in the circle, presumably showing when one is “pedaling squares” instead of more evenly.

My left was indeed generating more power than my right, but it sure didn’t feel like it, unless I actually took my foot off the pedal and could see a “zero” on that side. So I’m wondering if the pedals are not sufficiently accurate to use for improving/smoothing my stroke. At this point, I will simply start by following the old Quality Improvement maxim: “You only improve what you measure”, and take about 5 or 10 minutes at the end of every indoor session to look at the numbers when I’m cooling down. And continue searching for ways to confirm or refute whether I have an imbalance; if that imbalance is important; and what to do about it if it is.

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