Gym bikes - I don't get it.

They are measuring “watts” but it’s an approximation. They don’t actually have power meters. It’s not just wheel speed—they measure resistance. But there is no wind resistance, and only approximated changes in terrain. I don’t know all the details—I just know that it’s more sophisticated than you might think, but it’s not a power meter.

Not all gym bikes are the same though.
I use a Wattbike, not surprisingly given the name it measures watts accurately because it uses a power meter.

I normally export the data using the Wattbike Hub phone and online app but I can link my Garmin Edge 1000 if I want to.

This is the kind of data you can pull off.

NorthCascades wrote: »

I was curious to see what they had, so I checked them out. The bikes report watts as you pedal, but they're invisible to Garmins (over ANT+ and BT). So you don't get a record of what you did, and can't really analyze the data.

I have this suspicion that they're not actually measuring watts, they're probably measuring wheel speed and using a lookup table. That works pretty reliably indoors where you aren't affected by wind and traffic and hills. And it seems kind of silly to go to the trouble and expense of measuring power, and then not making it available.

Am I just being cynical?

When the market wants it...

https://lifefitness.com/facility/products/icg-series/ic8

Major equipment manufacturers (e.g. Life Fitness, Precor, Technogym) are always looking to balance features with cost. This is sometimes interpreted as meaning they are just “going for the dollars”, but it really is no different than any other business.

They are trying to include the features that the majority of potential buyers/users want, but cannot always include every feature that a niche part of the market would like. In addition, sometimes the technology either doesn’t exist or is too costly to include it for every exerciser.

There is also the question of reliability and durability. An commercial exercise bike is expected to last 5, 10, 15 years or more and will be used by thousands of people. It may not be possible to include a feature or a component just because it won’t stand up to the use. We have a lot of equipment at our center, probably more than we need given our membership numbers. Even with those modest numbers, our upright bikes are used 1,000-1,500 hours per year, so components need to be bulletproof.

In this context, the main concern is to have a system for applying resistance that is consistent, reliable, durable, comfortable, and cost-effective. The eddy current system mentioned in another post serves that purpose well. Whenever you work out, “100 Watts” will feel the same—not only on the bike you are on, but on any other bike as well. And “150 watts” is harder than 100 Watts, so if your average “power output” increases from 135 watts for a 20 min ride to 145 watts for the same time, you can assume that is a reliable sign of fitness/work capacity improvement.

Is it a precise “100 Watts” as determined by a performance-level power meter? Likely not, but that is not an essential feature. It is close enough for the average exerciser and provides a reliable benchmark for both workload and progress. In this case, there is not enough general market demand to justify the cost of something more accurate. And, for the general public, it’s not necessary.

There might be a smaller niche market of cyclists who want more precise data. That market is often then served by a specialty product, such as the Wattbike, or other trainers.

If market demand changes, then the companies will adapt. That seems to be the case with the new Life Fitness bike I referenced earlier. In group exercise classes, there is growing awareness of the importance of more accurate power readings, and increased demand for greater precision and ability to track workout details. That increased demand now provides a large enough market for a major manufacturer to justify creating a premium product to meet it.

If you want to talk about disabling/hiding existing product features for cynical reasons, let’s talk about iPhones...

NorthCascades wrote: »

Djproulx wrote: »

Late to this discussion, but I'm an interested party. I was not interested in indoor cycling until I found a studio that offers classes featuring a power based approach. Each session includes a 3 minute effort to derive a threshold number, or PTP, that is used to set interval efforts for the remainder of the session. (eg: 80% of PTP for 3 min, 120% of PTP for 1 min, etc.)

I've never heard of this PTP before. Sounds like you're training to be a sprinter?

Common practice (this isn't the only way and what you're doing sounds valid too) is that your functional threshold power (FTP) is the most power you can out (avg) for 60 minutes. And training zones are based on that.

Garmin devices automatically calculate your 20 minute MMP for each ride, and will graph this over time. It's a great fitness indicator. As you get fitter, you're able to put more power into the bike. Rule of thumb is most fairly well trained cyclists can do 95% of their 20 minute MMP for 60 minutes, but obviously everyone has a different fatigue profile.

PTP is the studio's abbreviated version of FTP. It is derived from a 3 minute hard effort. That way, the studio instructor can get a value for each rider at the beginning of each class, and riders can then work their individual efforts based on a percentage of PTP. The PTP values are shown on the big screen in front of class so the instructor can tell students to ride at 90-100% of PTP for 1 minute, etc.

I'm also familiar with FTP and my coach uses it to set my training zones. In fact, we had a special FTP session at this same studio, just for our triathlon group. During this time, we did a full FTP test. It was lots of "fun".

I'm not a sprinter. This off season, I'm going to work on becoming stronger on the bike in both watts/kg and endurance. My two A races for next year include hilly endurance ride segments: the REV3 Quassy (Half Iron distance) and the full distance IronMan race at Lake Placid.

NorthCascades wrote: »

Thanks (again) for the summary. I agree with pretty much everything you said. What you described is perfectly adequate for the average exerciser. A bona fide power meter with a maximum error of 1.5 % would be expensive and unnecessary overkill for most people, it's a niche requirement only a few of us want. I used the word cynical (and I was right in my guess) but I don't think it's poor form on the gym's or manufacturer's part, I was just making an educated guess.

Indoor bikes don't interest me anyway, I was curious how they're set up. I like cornering at speed, and scenery.

The things that are important to me from my PM are the normalized power for a ride, the training stress score, work done, and the power/duration curve - how many watts can I average for X minutes, X depending on the purpose of the ride.

It's hard to say what the average Joe ( or @JoRocka ) really wants. In some cases obviously not much or nothing. I would think a lot of people do want at least some type of repeatable performance metric for resistance and/or speed. More in depth types (like most of us in the thread) might want all types of balance, efficiency, true power, averages, etc. Similar to @Azdak I'd use a metabolic cart quite a bit if I had one. Maybe not for real training, but to engage in the geekery aspect of what goes on.

But for trainers or indoor bikes, this is where difference in equipment come into play. An eddy current system is fairly small and provides the resistance system as well as power measures within one unit. With a power inverter it can also supply power to the machine. They are a bona fide power meter, in fact they meter power going to millions of homes due to simplicity and accuracy. I'm not sure where the error averages are for lower powered units, but within 1-2% is easy. Many that measure auto power output claim error percentages within fractions of a percent, down in the .2 -.25% range.

These days I think the true power output and other data might be just as cheap to measure as it is to transmit and connect, and then of course integrate into software that makes it useful for us in some way.

Djproulx wrote: »

Late to this discussion, but I'm an interested party. I was not interested in indoor cycling until I found a studio that offers classes featuring a power based approach. Each session includes a 3 minute effort to derive a threshold number, or PTP, that is used to set interval efforts for the remainder of the session. (eg: 80% of PTP for 3 min, 120% of PTP for 1 min, etc.)

The Stages power meter pairs with my Garmin and I also get an email with results and my riding history. This allows me to integrate these rides into my Garmin data as well as with my home based trainer rides (I use Trainerroad) to get a more complete picture of my off season bike training. I'm not sure how quickly this type of studio will spread, but it will serve as my weekly high intensity workouts during the upcoming indoor season.

Here's a sample of the data. Couldn't figure out alignment, but the fields are bike position (8), ave rpm/max rpm, ave/max pwr, energy, miles, calories, then PTP(285 in first row).

Class

Thu 8/24/17 - 5:30 PM 8 85 112 216 520 647 13.3 806 285
Thu 8/10/17 - 5:30 PM 8 93 126 199 459 586 12.6 751 262
Thu 7/27/17 - 5:30 PM 8 95 135 198 478 578 12.4 744 269
Thu 7/13/17 - 5:30 PM 8 87 136 200 452 596 12.7 760 276
Thu 7/6/17 - 5:30 PM 8 89 115 198 433 584 12.7 749 262
Thu 6/8/17 - 5:30 PM 8 97 147 181 476 544 12.3 713 248
Thu 6/1/17 - 5:30 PM 8 96 136 185 459 488 10.7 663 245
Thu 5/18/17 - 5:30 PM 8 96 132 190 460 560 12.4 727 254
Thu 5/4/17 - 5:30 PM 8 91 128 190 489 553 11.9 721 271
Mon 2/20/17 - 6:00 PM 8 91 120 146 470 602 15 803 216
Mon 2/13/17 - 6:00 PM 8 90 123 175 405 677 15.7 870 251
Mon 2/6/17 - 4:30 PM 8 88 114 196 557 567 12.3 734 277
Fri 2/3/17 - 7:00 PM 8 86 123 156 398 537 13.1 722 0

Interesting approach. Do they have "Named" or somehow identified interval sessions so you could keep track of them easily, or do they just vary with no ID involved? What type of bikes are they using? It sounds similar to some of the stuff Wattbike advertises that is designed for groups.

Sounds like a cool approach to me. I think I'd sign up for classes just to get the true power measured PTP/FTP estimate number.

Power is easy to measure directly in mag resistance bikes. They basically have generators on them. High load, more power output. Power =V^2/Rload.
I'm not sure if a given bike uses mechanical or magnetic field resistance.

kcjchang wrote: »

PTP training sounds like traditional VO2MAX imtervals but cannot tell based on the description on the number of reps and duration of rest. Also, what's the point of training at power that's significantly below your 3 minute mean maximal power (MMP)? If so why not move to 5 or 8 MMP?

One thing not addressed is the consistency and accuracy of the power measurement. Both are important. https://roadcyclinguk.com/how-to/fitness-nutrition/power-meter-really-telling-think.html.

It's a shame some of that power meter testing is behind a pay wall. For what some companies charge for the meters people should know the real accuracy levels of the meters. But the article alone has some good stuff.

fishgutzy wrote: »

Power is easy to measure directly in mag resistance bikes. They basically have generators on them. High load, more power output. Power =V^2/Rload.
I'm not sure if a given bike uses mechanical or magnetic field resistance.

And as a bonus, most of the factors that influence magnetic resistance are easy to control when only measuring human powered devices. Though the size and design limit them to indoor type equipment, for that purpose they are great devices.

Djproulx wrote: »

kcjchang wrote: »

PTP training sounds like traditional VO2MAX imtervals but cannot tell based on the description on the number of reps and duration of rest. Also, what's the point of training at power that's significantly below your 3 minute mean maximal power (MMP)? If so why not move to 5 or 8 MMP?

At the studio I described, most but not all intervals are run at or slightly above 100% of PTP. After the 10-12 minute warmup spin and 3 minute PTP establishment segment of a ride, a typical sequence might include a 4min block at 90% of PTP, brief recovery ( say30sec-1 minute), then various shorter intervals usually done at 100% or above. Often, the sequence is repeated twice during a 50 minute class.

That sounds like a cool setup. Kind of the Orangetheory of biking, but with individual power based metrics.




@sijomial Are you using those new Wattbikes that also have the air resistance? It seems like a cool feature, even if it is a strange way of accomplishing the goal. I'm surprised that the idea of increased resistance with speed isn't built into more devices, as it seems it would be fairly easy to do.

@sijomial

Thanks for the response. Those things look like quite the machine, but I've yet to even see one of the new ones. I also wondered about directing the air.... it's a free fan for a couple more dollars!

Surprising that they would use a gross calorie formula, given the name of the thing. But our elliptical is the same. Since I can't use your workaround of exporting the data, I just found a calculator that lets me subtract 1 MET and go with that as the closest true calorie figure/power measure.

After some reading, I found they use a chain type power meter. From my understanding they just pick up the vibrations of the chain based on load. I don't know if I've even seen one in person, but it gives me another reason to want to check out the Wattbike.

Based on your power numbers I don't think that wonky left knee is hurting you much. I'd love to have that much data from a bike/trainer!