Magnetic Resistance Exercise Equipment

Does anyone know anything about the EMF output of magnetic resistance exercise equipment? I'm referring to mostly manually operated exercise bikes and treadmills where the flywheel tension is altered by magnetic resistance as opposed to full-powered electric or basic tension resistance equipment.

Yes. I recently disassembled an old Minoura Magturbo trainer did a bunch of tests on it. Here's a picture of the brake mechanism:



(The weird color is due to some plant lights nearby.)

Without any modification, the low frequency magnetic field strength right next to the brake was 10 to 12 microteslas (uT).  Replacing the three screws on the right of the photo with non-magnetic (stainless steel) ones lowered it to 4-5 uT. Vibration makes a pretty big difference, too.

I also have a Kinetic Road Machine fluid trainer that's about 10 years old, and although it's supposed to have a magnetic coupling inside, it only generates a 5 uT magnetic field. (For that reason I'm pretty sure that it *doesn't* have a magnetic coupling. It was a production sample that I bought directly from Kinetic's North American sales director, so it's not 100% identical to a normal Road Machine.) The safest bike trainer would probably be a Cyclops from that period, since they had fluid resistance units and no magnetic couplings as far as I know. I can't help much with treadmills or elliptical machines.

That's pretty high. Is that measurement taken right up against the mechanism? Any data from varying distances? Since there's no electricity involved, I wonder if it's a non factor for ES? Or is it creating electricity by the resistance? What was your experience?

Miller wrote

That's pretty high. Is that measurement taken right up against the mechanism?

Yes, touching the hub.

Any data from varying distances?

I do, but it's probably not very useful to you. I had it hooked up to a Servodisc motor that produces about 1.4 uT.

Since there's no electricity involved, I wonder if it's a non factor for ES? Or is it creating electricity by the resistance?

That's how they work, unfortunately. (en.wikipedia.org/wiki/Eddy_current_brake)

Their only saving grace is that the electric current in the disc is DC and stays in the same place. If the disc were perfectly symmetrical and rotated at a constant speed, the field near it would be like a bunch of permanent magnets. Unfortunately the disc in the Magturbo has a lot of vent holes that shift the current around as they go by the permanent magnets, which rattle at the same time.

What was your experience?

I didn't like using either trainer, but I had them in an area with wiring problems.

Very interesting, but in a bad way. Thanks for the info!