No it's actually a lot more complicated than that and it's also a reason why other single sided PM brands/models don't offer L/R balance. The PM only knows if one side is putting power or not, that's it. To conclude that the other side is always putting exactly the same power skews the L/R stats. If you buy the assioma UNO (which is pretty much the golden standard for PM accuracy) you'll notice they don't provide L/R balance for that reason, because it's not possible to get accurate data. That's also why in the assioma app you can specify a L/R power balance if you know you're always outputting 45/55 for instance. This way the uno won't simply *double* your power but will use this ratio.
Think about it this way, with your logic you could be doing one-legged workout (where you only have one leg clipped in) and the single side power meter would think you're applying power on the other side when you don't even have a foot clipped on the other side. Single side powermeter will never be accurate for L/R balance because it can only tell if one side is putting power or not.
I've had assioma duos. During high intensity workouts/sprints it's very common to get an imbalance on the power because people tend to have a stronger leg/side.
Well, that is not quite correct. You are talking about a
one-sided pedal based power meter - there you are correct; they double the one-sided reading to get total power. Which of course is a "guesstimate" since that only works if you apply power completely even. And since it truly is a one-sided measurement, it cannot provide any L/R-balance.
But a
spider based power meter does not do that. It sits, as the name suggests, at the spider or the axle if you prefer that. Therefore, it does not only get the applied power from one side (as in on a crank or pedal reading) but from both sides as it sits in between. And since it also knows which side of the crank is currently in the down/up-stroke movement, it can attribute that power to the respective side. It is not 100% exact as in a dual-sided crank/pedal reading, since you could influence the reading for example by pulling on the pedals. However, the amount of power you can apply by pulling compared to pushing on the pedals is so small, it really does not matter much. Furthermore, as I mentioned before, pulling on the pedals should be avoided anyway since it is energy inefficient.
To pick up your example with that one-legged workout: doing that on a spider based PM, like the Magene here, will actually give you correct data. And will also show quite a hefty L/R imbalance depending on which foot you keep "inactive".
What a spider based PM cannot measure (and therefore will also not show up in their data), are the other cycling dynamics stats like Seated/Standing Position, Power Phase (PP), and Platform Center Offset (PCO) as they are truly pedal dependent measurement. Hope that makes sense and clears up a few misunderstandings?
