Initially introduced around 2015, independent left/right power (L/R power) measurement is a feature that has found its way into more and more power meters. With left/right power measurement, the power meter can measure how much power you generate from your left vs. your right leg. Pretty cool right…yep! However, there are different types of left/right data depending on your power meter. Then there’s also the question of what you do with this data once you have. This article aims to sort through some of this. So let’s get started.
Left/Right Power Measurement
Not All Left/Right Power Measurement is Created Equal
To begin with, there are two types of L/R power: actual and estimated.
Actual L/R Power
With actual left/right power, the power meter is able to determine exactly how many watts your left leg is responsible for and how many your right. To get this independent power measurement, it reasons that your power meter must have two, independent sets of power sensors (strain gauges plus electronics) on the power meter – specifically one on each side of the drivetrain. This can be accomplished in a few ways. One is through dual-sided power meter pedals (Favero Assioma DUO, PowerTap P1 or Garmin Vector 3). All of these power meters contain strain gauges in both the left and right pedal. Therefore, they are able to determine your exact power distribution.
Another method for measuring actual left/right power is through dual-sided crank arm-based power meters. Take the Verve InfoCrank for example. Verve locates a load cell in each crank arm. Two load cells = true left/right power. ROTOR takes a slightly different approach with its 2INpower DM. ROTOR locates one power sensor in the axle (which is responsible for measuring left leg power), and one power sensor on the right crank arm (for right leg power). Again, two power sensors so you have true L/R power. 4iiii, Stages and Pioneer all have similar configurations whereby they measure independent left/right power on their complete crankset offerings by locating one sensor on the left crank arm and one on the crankset or on the drive-side crank arm in the case of 4iiii.
Estimated L/R Power
Then there’s estimated left/right power. Take the PowerTap C1 Chainring for example. The C1 measures power at the chainring. But how can one sensor, located on the chainring, tell how much of your power is coming from each leg? Well, it can’t exactly, but it can get pretty close by making some relatively simple assumptions. What the C1 does is it essentially “credits” the power that is being generated at any point in time to either your right or left leg based on where in the pedal stroke you are at.
If that sounds complicated it’s really not. The C1 takes power from your left and right down strokes only, and ignores the up stroke. So during your left down stroke, the power meter credits the power to your left leg. Likewise, during your right down stroke, the power meter credits the power to your right leg. Since the majority of your power comes from the down stroke, it can estimate the power distribution fairly closely using this method, just not exactly. The FSA PowerBox uses similar technology in estimating your power distribution.
Here is a breakdown of which power meters can measure left/right power:
Actual L/R Power
Estimated L/R Power
1. PowerTap is listed twice because their P1 pedals measure actual L/R power, whereas their C1 Chainring measures estimated L/R power.
2. PowerPod doesn’t display left/right data in real-time on your head unit like the other actual L/R power meters on this list. However, using its PowerStroke software (a $99 upgrade), you can analyze left/right power as well as other data, post-ride
Left/Right Power Pros and Cons
The advantages to left/right power are obvious enough. You have all the workings of a complete power meter, plus the added benefit of independent left/right power data. Not only is having this data fun (let’s be honest!), but if you can figure out how to benefit from this additional data, you can become a stronger, faster rider (more on this to come). In addition, we’ve seen that left/right power data can be helpful when recovering from an injury.
However, for the sake of completeness, we want to mention the downsides here, even though they’re limited. When purchasing a power meter capable of left/right data, you should realize that your risk of problems increases (at least in theory) since you will have multiple power sensors on your bike. (Note however that we have had great success with all the left/right power meters we sell – so we view this risk as fairly remote). In addition, left/right power meters can be heavier as they contain two power sensors and two batteries. But we’re talking just a few additional grams here so we don’t think it’s anything to get hung up on.
What to Do with Your Left/Right Power Data
Determine Your Real L/R Distribution and Analyze
So your power meter measures left/right power data…great. But now what? Just having a power meter with this capability isn’t going to make you a stronger, faster cyclist. Nor is merely glancing down at your power balance from time to time during your ride. Putting your left/right power data to good use is essentially a two-step process. First, you must determine what your true left/right power measurement is. Second, you need to work to address any imbalances that might exist – should you determine that the imbalances are indeed an issue. (Remember, almost all cyclists have some level of imbalance. For example, a power distribution of 52/48 isn’t anything to worry about. A distribution of 60/40 on the other hand might be worth looking into.)
However, determining your real left/right power distribution isn’t as simple as taking your average left/right power balance from your last ride to the coffee shop. Your power distribution can fluctuate based on a number of factors including seated vs. standing; pushing hard vs. taking it easy; fresh vs. fatigued; high vs. low cadence and more. You need to perform some proper tests in order to gain a clear understanding of your left/right power distribution across these different variables. Once you have the data, it’s time to crunch some numbers and put together a plan to address any weaknesses.
Coach to the Rescue!
But don’t fret if this sounds like a lot…there’s help. We often talk about the reasons to hire a coach and how important they can be. The value they can provide, especially when training with power, can be substantial. Helping you make sense of your left/right data is yet another example of how they can help. We would note however, if searching for a coach, make sure they have some experience in this field. Some coaches will be more versed in this area than others.
If you’re looking for a recommendation, we would tell you to give Peaks Coaching Group a call. Hunter Allen, founder of Peaks Coaching Group and co-author of Training and Racing with a Power Meter, has been studying left/right power data extensively for over three years. He has worked with the core development team of TrainingPeaks’ WKO4 software to create new analytics and unique charts and graphs. This data allows him to more completely understand how each leg contributes to total power. Needless-to-say, you would be in great hands with Hunter or any of his coaches!