Stunning difference in power R vs L

I was borrowing Garmin power meter pedals for a while just for curiosity's sake. We finally got around to extracting the data and I'm sorta shocked to see the imbalance in power between my right and left legs. We're talking R:L ~65:35 (even 55:45 would be considered significant, from what I gather). I'm guessing this issue goes back to well before my cycling lifetime. When I first started running and started to increase my mileage and suffer overuse injuries they were ALWAYS on my right side. But I have sprained my left ankle twice. Which makes me think that for some reason my right leg has been doing the lion's share of the work for my weak left side.

So...this has me wondering why one side would be so much stronger than the other. I have long suspected that my right leg is longer than the left. Would that be enough to explain this, or should I be looking at something else? Does it even matter, or am I risking major problems (ie back, hip, knees, etc.) down the road?

I suspect you are right to be concerned. Now, I don't know anything about anything, but I can relate my own experience with a big disparity in output between legs. For years (maybe 3-4) I noted that my left leg was significantly weaker than my right. My left leg was so much weaker that it left marks on my bike where my heel would strike the crank arms. Deep grooves. Long story short, herniated disc later, referred pain all on the left side, lesson learned. Lots of strength training focusing on core and back body and such and my body is so much more balanced and a lot of my issues are resolved. Look into it!

Do the pedals still need to be properly torque wrenched on or you can get misleading data? The Garmin forum may also have more info on power imbalance and even the multi step installation procedures.

How were your muscles before/during the ride you got the data on? Muscle fibers in one leg that are tight and shortened may be unable to produce equal power to the other leg. That’s one reason on long hard rides I stretch quads, hamstrings and glutes during the ride to keep muscle length-tension. Could you sense if you were pushing and pulling on the pedals equally with each leg?

At least you may have gotten a warning that something may be going on so you can take measures to improve the balance in your pedaling biomechanics.

You may want to pm Wahine about it, especially the leg length difference.

We didn't do a great job with calibration/installation. So it's something I may try again. Perhaps the discrepancy isn't as great...though we saw similar #s when I had them on the back of our tandem, too. I had the pedals on my road bike for 3-4 weeks, so we were able to see data from a lot of rides -- easy, pace line, race...

I have a weak left leg due to knee injuries. I am lucky to live across the parking lot from an excellent sports medicine chiropractor. Between Gastron treatments and tons of exercises to actually improve my left hip strength it is finally starting to get better. However two weeks ago I irritated a nerve in the bottom of my left foot on our very rocky, challenging desert overnighter so now I am cussing.