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Power data and left right balance of a recent exercise

In case it is not clear for everyone, let me briefly explain the graph. The pink line represents the Power output along the y axis while the grey dots represent Left/Right balance in Power. The x axis represents time.

I was aiming for 360 watts in the beginning. Assuming I had a single-sided Power Meter (for my right leg) it would have showed smaller numbers where the Power Balance was more towards my left leg.

The direct consequence in holding a specific amount of watts using a single-sided Power Meter would be that as the Power Balance shifts away from the leg with the Power Meter, the total actual Power will go up while the numbers remain the same. As the Power Balance shifts towards the right leg total Power goes down.

The indirect consequence is the mind would subconsciously (or even consciously) learn to use the right leg more than the left leg. Especially in those crucial moments, like the last 15 seconds of an interval.

I'm looking for evidence to backup my claim. And since I am 100% certain that I am correct, why do people use single-sided Power Meters? Why do they exist at all?

AzulShiva
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    Single-sided power meters exist because they're less complex and therefore cheaper than dual-sided ones. – Criggie Oct 31 '16 at 21:20
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    @Criggie that's not exactly the full story: the first power meters measured total combined power because it was easier to measure that way, and even today some power meters that measure total power can be cheaper than some that measure only one side. A better description for why they exist is because of patents: earlier devices locked up measurement at the crank spider, the rear hub, and the chain. That mostly left the BB, the cranks, and the pedals, which are more complex, as you correctly say, so opened a window for measuring only one side. – R. Chung Feb 05 '17 at 13:05

2 Answers2

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I am unaware of any controlled study that directly addresses your question.

However, a recently published study by Bini et al. addressed the converse of your question: can the provision of information on bilateral symmetry or asymmetry be used by riders to alter their pedaling dynamics? The Bini et al. study did not address whether riders would benefit from decreased bilateral asymmetry -- it only addressed the limited question of whether it was changeable. The answer appears to be that it can, sometimes. So although your exact question was not addressed, if these results are replicated and verified then a reasonable implication is that if one were to supply the riders with incorrect or misleading information on symmetry the riders might also be able to adjust their pedaling.

R. Chung
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Single-sided power meters have existed since the "year dot" - and opposite leg power is often "extrapolated" from a single strain gauge

And given most power-meters will quote accuracy to be within X% - the use of left and right strain gauges means although accuracy could be within X% of both left and right - it causes problems with precision. So the maximum variation between both strain gauges could be LEFT DRIFT + RIGHT DRIFT.

(But both being within X% of true strain).

So there is an argument which questions whether left and right power meters are in fact more accurate. And it is possibly the magic of the software / firmware further downstream from the strain gauge signal which provides a coherent reading.

From your graph you have posted - you have tight banding of power on the left leg which indicates a smooth pedal stroke on the left-side. Your right side looks choppy like you're stamping on the pedals. This is often described as "pedalling squares".

The important thing with power meters is precision (consistency) of the reading.

In direct answer to your question - why do people use single-sided power meters - it has inherently been the cost of dual-sided power measurement. However, in the last 2 years - cheaper pedal-based systems have appeared from Garmin and more recently Favero.

OraNob
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  • I am neither talking about precision nor consistency. Please read the question again – AzulShiva Oct 31 '16 at 12:33
  • Read the answer - all of it is relevant to your question

    Single-sided power meters are used due to economics of producing dual-sided strain gauges. And they offer consistency / precision of reading - which is the one of the most important aspects of the tool (unless you are comparing data from rider to rider).

     – OraNob Oct 31 '16 at 12:39
  • The problem with Power meters that only measure Power on one side is that the other leg becomes irrelevant. Wether you're doing 52/48, 60/40 or 90/10. If you rode to power on your right leg and an alligator bit your other leg off you wouldn't even notice regarding Power. And the problem I have stated is that when you ride with one sided power meters you will unvoluntarily end up doing 55/45 because that is what the power meter has trained you to do and you will end up a miserable cyclist. – AzulShiva Oct 31 '16 at 12:54
  • Your assertion and analogy is just wrong. You are assuming a 100% dead-spot in power for the opposite leg (on the up stroke) at the point your driving leg (on the down stroke) makes maximum power.

    If you have ever done single leg drills - you will really notice how much the opposite leg contributes to the full stroke of the other leg. Besides - you should not be consciously riding to target a specific side because you know a power meter is on that side. That is not the way to train with a power meter.

     – OraNob Oct 31 '16 at 13:06
  • I'm not sure what you mean by "year dot." In the context of Azul Shiva's question about bilateral asymmetry, the SRM, for example, is not "single-sided." It may be mounted on one side of the bike but it measures total combined power generated by both legs, not just the left or right legs. Power meters that exclusively use sensors mounted in the BB, the left crank, or the left pedal are often referred to as "single-sided." – R. Chung Oct 31 '16 at 22:25
  • The incoherence of your posts is absolutely out of this world. Flagged for low quality. – AzulShiva Nov 01 '16 at 12:53
  • Well hopefully you can concentrate more on turning circles instead of right-leg squares. Best wishes. – OraNob Nov 01 '16 at 13:15
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    "Low Quality" is different to a wrong answer or a poor or irrelevant answer. Consider using the up/down votes instead. – Criggie Nov 01 '16 at 20:21
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    OraNob: i. as RChung pointed out, your use of the term "single-sided" is misleading. There are 2 ways to measure total (both legs) power, each based on location of force measurement (upstream or downstream of bottom bracket), see: http://alex-cycle.blogspot.com.au/2013/11/left-right-out-of-balance.html single sided = upstream on one side only ii. pedalling asymmetry & variable asymmetry is normal, hence true single sided meters can never be consistent; iii. you can't infer pedalling style from the OP's data. Such data does not have the temporal resolution to enable such an assessment. – alexsimmons Nov 01 '16 at 21:36
  • http://www.cyclist.co.uk/news/1416/how-advanced-does-your-power-meter-need-to-be

    "When the strain gauges of a power meter are placed at the crank spider, hub or chainring it is difficult to isolate the forces each leg is applying individually. These systems largely generate a balance figure by separating the power in the first 180° of the crank rotation from the power in the second 180° of the rotation, and calculating a consequent balance between the two. That’s a fairly accurate measure, but does not fully consider that a rider may be exerting force on the upstroke."

     – OraNob Nov 01 '16 at 22:01
  • "Allen says, ‘The true left and right meters now, as far as I know, are the Garmin pedals, the Powertap pedals, the Infocrank and also the Pioneer crank.’" quoted by Allen from the same article. And if twin strain gauges is the only true measurement AND each strain gauge will have a quoted accuracy of X% - a valid question & point is how accurate is a measurement of pedal asymmetry - if you are only staring at power? And if you don't have twin strain gauges in your hardware. – OraNob Nov 01 '16 at 22:09
  • And as for describing my response as "low quality" - I can only measure that response from the OP as my answer not being the answer he wanted to read. – OraNob Nov 01 '16 at 22:11
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    OraNob - It's clear you did not read the link I provided. Please read it first before telling me what I already know and have taken the time to explain in a manner that can't be done in a comment.

    I voted on your answer accordingly as it contains factual errors and is misleading, not because it's not what someone wanted to hear.

     – alexsimmons Nov 01 '16 at 22:51
  • This guy is a waste of time. – AzulShiva Nov 02 '16 at 14:11
  • This guy measures his wattage with a silent "T" – OraNob Nov 03 '16 at 11:06