I've just started using my spinscan the other day and asked a similar question about the validity of the numbers. When I just pedal I get something in the high 50s to mid 60s. When I did get the number to go into the mid 70s I did feel a different overall pedalling motion, but I haven't done it enough to figure out what the real value of it is.

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http://bigisland-will.blogspot.com/

exactly what spinscan is supposed to do, show you what makes a smooth pedal stroke even if it's not what you expect:) Haven't been on one in a while but I remember the sensation you're talking about. Correcting one leg tends to smooth out my other as well. The scraping mud at the bottom is important but you need to work on the whole stroke as well, scrape on one foot and roll the other over the top or something like that. Anyways, that happened to me too. It's a really really useful tool though. Wish I had one.

"why would the leg that i am concentrating on "at the bottom" not go up?"

Because you're 'forgetting' about it on the backside and over the top. Pedaling through the bottom of the stroke is only part of the equation...pedal over the top as well... If we're talking about a pedal stroke in a counter-clockwise measure...then I think 90deg and 270 are more important points to 'break' the stroke from...At 90 you are in your power band and at 270 you are in recovery...those take care of themselves somewhat...its what you do between those two points that differentiates good and bad strokes.

Also understand that spinscan can 'lie' about your stroke...just because you can make good numbers...that doesn't mean that you are efficiently applying that power to produce forward power...you may be controlling your efforts between legs, evening out the power application, sometimes even with pressure against the leg in the main powerband on the downstroke...

spinscan assumes all the power comes from the downstroke portion of the circle - it must of it cannot separate right from left. Any lifting that is done on the upstroke is seen as pushing on the other leg. Once you are past the bottom on your scraping the mud off you will improve the other leg from this maneuver according to spinscan. Want proof? pedal with one leg and watch spinscan.

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Frank,
An original Ironman and the Inventor of PowerCranks

I do not know how spinscan works, but it helped me to use more of the muscles in my legs and get more power and speed.

Greyhound,

I have really been focusing on Spinscan in my winterworkouts, and noticed the same thing. If I understand the manual correctly, the left side of the bar graph represents the efficiency of your stroke (power being applied at a point in the stroke divided by the maximum power at any part of the stroke) as your left leg moves from 12:00 to 6:00. But I think I get what Frank is saying. You cannot isolate the efficiency of one leg (unless, Iguess, you were doing one-leg drills). So focusing on your right leg may result in the readings on the left side of the graph to change.

When I started this focus, my efficiency readings sucked too. I was averaging over 200 watts but had consistent efficiency readings in the 50's. So for a few weeks I ignored the power readings, dropped down into a very low gear and just focused solely on the spin. I also adjusted my set up (on my tri bike) a bit to help open my hips and make the stroke a little smoother. Over the course of a few weeks I "willed" my stroke to be more even and was able to get the efficiency readings into the 70s. No I am beginning to apply more power to my pedal stroke while trying to keep the stroke smooth and efficient.

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Rich Strauss give a really good reply on Gordo's web site.

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http://bigisland-will.blogspot.com/

Yes, what Frank says. Also, SS numbers are merely average torque divided by peak torque. In other words, showing how evenly you apply power. My numbers are usually high 60s in easy gears, high 70s in bigger gears, and mid-80s if I try to pedal in circles intentionally (or more specifically, if I try to roll over the top).

I'm not so sure that higher SS numbers really are that important.

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Too f@ckin depressed from various injuries to care about having a signature line.

Sponsored by Blue Shield PPO.

I found that when I make a conscious effort to push over the top of my stroke, everything else falls into place.

How does it "know" i am doing 1 leg drills? When doing those drills it shows sppinscan for only 1 leg.

Useless feature.

[reply]How does it "know" i am doing 1 leg drills? When doing those drills it shows sppinscan for only 1 leg.[/reply]

It doesn't know and you are misinterpreting what you are seeing. Spinscan measures smoothness, not efficiency, and the relative net strength when the right the or the left legs are pushing (which will include the other leg pulling).

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Frank,
An original Ironman and the Inventor of PowerCranks

Exactly. As I said before, it's merely average torque applied over the entire stroke divided by peak torque.

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**************
Too f@ckin depressed from various injuries to care about having a signature line.

Sponsored by Blue Shield PPO.

When I 1 leg pedal, I get zero on the side I am not pedaling on, and regular numbers on the side I am pedaling on. How am I misinterpereting that?

[reply]When I 1 leg pedal, I get zero on the side I am not pedaling on, and regular numbers on the side I am pedaling on. How am I misinterpereting that?[/reply]

It is very unlikely you are actually getting zero on the other side but even if you are all that means is you are not pulling up at all (zero). If that is the case you better do a lot more one legged drills cause you need them. :-)

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Frank,
An original Ironman and the Inventor of PowerCranks

Your Computrainer is smarter than Frank Day.

(the following is speculation)

Seriously, the Computrainer probably assumes that there will be two power spikes per revolution (it knows your cadence through a sensor, right?). It assigns each spike to a pedal depending on where relative to the sensor each pedal is, and can therefore figure out the force exerted on that pedal. With single leg pedalling, there is only one spike per revolution; it will always assign the force to the pedal associated with that spike. I'll bet that it would get seriously confused if you were to hook your cranks up to a motor.

I asked the Power Tap people about how they do virtual cadence and why it was so wrong when using a trainer with a flywheel (that smoothed out the power spikes), and this kind of explanation was given.

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"Go yell at an M&M"

   

Along those lines......when I put my mongo 18 lb flywheel on the Computrainer, my Spinscam numbers magically improved by about 20 points.



-jens

[reply]ously, the Computrainer probably assumes that there will be two power spikes per revolution (it knows your cadence through a sensor, right?). It assigns each spike to a pedal depending on where relative to the sensor each pedal is, and can therefore figure out the force exerted on that pedal. With single leg pedalling, there is only one spike per revolution; it will always assign the force to the pedal associated with that spike. I'll bet that it would get seriously confused if you were to hook your cranks up to a motor. [/reply]

The CT algorhythm is actually quite simple. The pickup is when the left crank is on the mid part of the upstroke and it can time how long it takes to do one revolution. It assumes the pedal speed is pretty much constant such that if you divide that time in half that is when it will find the right crank at the mid point of the upstroke. further, it can calculate where each crank is at any time of the stroke as long as cadence is constant (most of the time). It then looks at variations in wheel speed during this period (it learns how fast the wheel slows down when no power is applied when it is calibrated) and, using the assumption that power is only applied on the downstroke, can calculate the applied torque at any pedal position.

Driving the pedals with a motor wouldn't confuse the CT or spin scan at all, and the resultant spin scan number would be 100 and it would be divided equally between right and left.

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Frank,
An original Ironman and the Inventor of PowerCranks