Which PM for right/left asymetry measurements

[hmronnow]

Hi,

I'm considering to buy a power-meter option.
However, in addition to the power-training, my purpose would be to monitor right/left leg asymetry. My left kne got botched in a mountaineering accident (ACL reconstructed etc.), and since I have the impression that I'm not cycling symetrically.

1) Which of the available products provide best data on right/left asymetry?

2) Even if it is not the best for asymetry, I'm impressed by the new wireless power-tap (I always hated those wires all over the bike). Does this one provide any kind of asymetry data?

Thanks
Henirk

 

[Spunout]

The computrainer 3D (and other fixed ergos? Velodyne?) has a spinscan function where you can analyze left/right power in a few different (neat) graphics.

I am not aware of any on-bike PMs that can perform this. The reason is that the sampling rate must be very high to get torque around the pedal stroke.

 

[acoggan]

The computrainer 3D (and other fixed ergos? Velodyne?) has a spinscan function where you can analyze left/right power in a few different (neat) graphics.

I am not aware of any on-bike PMs that can perform this. The reason is that the sampling rate must be very high to get torque around the pedal stroke.

The Computrainer can't really distinguish between the actions of the legs, as all it senses is the net power that makes it to the rear wheel. Thus, if it shows your pedaling to be asymmetrical, you don't know if that's because you're pushing harder with one leg, or pulling harder with the other.

Although it claims to give L/R balance, the Polar S7XX on-bike powermeter suffers from the same limitation as the Computrainer.

 

[RapDaddyo]

The Computrainer can't really distinguish between the actions of the legs, as all it senses is the net power that makes it to the rear wheel. Thus, if it shows your pedaling to be asymmetrical, you don't know if that's because you're pushing harder with one leg, or pulling harder with the other.

Although it claims to give L/R balance, the Polar S7XX on-bike powermeter suffers from the same limitation as the Computrainer.

Andy, I thought I read that the SRM Pro has an optional feature that can be used on the trainer (because it needs to be hard-wired to a PC) that gives at least some data on the torque for both L & R crank arms.

 

[scotmart]

Andy, I thought I read that the SRM Pro has an optional feature that can be used on the trainer (because it needs to be hard-wired to a PC) that gives at least some data on the torque for both L & R crank arms.

The SRM with torque analysis does the same thing as the computrainer (real-time net torque) and thus suffers the same limitations.

The only PM that could potentially offer actual l-r differential is the Ergomo in that it only measures one side. To get the info though would require one to accept that the Ergomo is accurate in its measurement (in refernce to the second point...), and would require another PM to give a net torque from which l-r balance could be derived.

So, the short answer to the OP is there are no PM's that can give the info he desires. You need force pedals.

Scott

 

[tigermilk]

The Computrainer can't really distinguish between the actions of the legs, as all it senses is the net power that makes it to the rear wheel. Thus, if it shows your pedaling to be asymmetrical, you don't know if that's because you're pushing harder with one leg, or pulling harder with the other.

Although it claims to give L/R balance, the Polar S7XX on-bike powermeter suffers from the same limitation as the Computrainer.

It is better than nothing, however. I first bought a Computrainer after breaking my hip in a crash. It was great during the recovery process since the l/r was good enough to gauge my strength recovery.

One thing, however, is that the CT doesn't just use power at the rear wheel. If you disconnect the cadence sensor you will not get the l/r function. I'd tend to think if the software makes some assumptions on force through the stroke, the addition of cadence yields a better l/r estimate. For example, if the cadence sensor is picking up at the 8-9 o'clock position and you assume the majority of power is coming from the downstroke (2-3 position on right side) the l/r estimate is reasonable. Also, even though the spin-scan is a bit suspect, you can certainly alter your pedaling style to alter the results (i.e., more downstroke, more upstroke, more circular).

Realistically, wouldn't someone tend to push more on one leg rather than pull harder with one leg?

 

[scotmart]

It is better than nothing, however. I first bought a Computrainer after breaking my hip in a crash. It was great during the recovery process since the l/r was good enough to gauge my strength recovery.

One thing, however, is that the CT doesn't just use power at the rear wheel. If you disconnect the cadence sensor you will not get the l/r function. I'd tend to think if the software makes some assumptions on force through the stroke, the addition of cadence yields a better l/r estimate. For example, if the cadence sensor is picking up at the 8-9 o'clock position and you assume the majority of power is coming from the downstroke (2-3 position on right side) the l/r estimate is reasonable. Also, even though the spin-scan is a bit suspect, you can certainly alter your pedaling style to alter the results (i.e., more downstroke, more upstroke, more circular).

Realistically, wouldn't someone tend to push more on one leg rather than pull harder with one leg?

It's been discussed several times here I think....but the gist is...

Imagine these scenarios for the pedals at 3 and 9 oclock...

R@3 pushing at 100 units, L@9 negative 20
L@3 pushing at 100 units, R@9 negative 10
L/R reported 53/47, actual 50/50

R@3 pushing at 120 units, L@9 negative 20
L@3 pushing at 100 units, R@9 negative 10
L/R reported 47/53, actual 45.5/54.5

R@3 pushing at 105 units, L@9 negative 20
L@3 pushing at 95 units, R@9 negative 10
L/R reported 50/50, actual 47.5/52.5

Now of course, 'actual' is only the ratio of downforce, and the magnitude of the negative upstroke is exaggerated in these examples (for most people). But, the point still stands, the number you get doesn't really tell you what the individual legs are doing. And to further muddy the water, if one were to use it for rehab, there is no guarantee the relative values of the forces involved (downforce to negative upforce) would stay constant. I can imagine scenarios (depending on what one happens to be rehabing from) where the 'numbers' might get better, when in fact there is a worsening imbalance.

The only value spinscan has is in increasing the amount fitters seem to be able to charge when they advertise using it as part of their evaluation =).

Scott