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Is the workout quality better when using an exercise bike or trainer with less flywheel weight?

With less flywheel weight such as a bicycle on a trainer as opposed to spin bikes, coasting is harder. This should make it easier to learn to pedal smoothly and not coast which are encouraged. Because our muscles work longer, it seems like it's more effective for improving our endurance for the same workout duration and getting more exercise out of the same amount of time. We might expect working our slow twitch muscles more and using our fast twitch muscles less.

If dead spots make it an issue, can shorter cranks or oval chainrings be substitutes for flywheel weight?

Update: When I say pedalling smoothly, I meant in terms of power output throughout each pedal stroke.

With a smoother pedal stroke, would it actually decrease normalized power?

  • Trainers of decent quality generally use magnetic resistance or fluid resistance; lower quality ones are wind trainers. Kurt kinetic has a flywheel unit you can add to their fluid trainers, which they claim gives you a more realistic ride. It's harder to pedal smoothly on a trainer than it is on the road in my experience. And exercise bikes are quite different in quality. – Batman Dec 7 '17 at 2:34
  • Besides feeling more realistic, are there other benefits of having a flywheel? – Han-Lin Dec 7 '17 at 5:29
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Workout quality is determined by the power output you can sustain through the course of your effort(s), and if the power is lower than it might be because of a lack of crank inertial load, then the training stimulus will be less.

Keep in mind that the most important adaptations are metabolic, not neural. Changes to pedalling action has not been shown to convert to improved power output, except for the specific situation being trained.

It's common for people to find riding on low inertia trainers (e.g. cheap magnetic resistance units) unable to generate the same power as when riding a high(er) inertia trainer. The crank inertial load doesn't need to be as high as that experienced in typical outdoor riding, just sufficient to avoid that awful draggy sensation.

There are quite a number of published studies about varying crank length and chainring shape. The balance of evidence on these is that on average, such interventions neither harm nor enhance your sustainable or maximal power output.

As a general rule of thumb, if you find using a trainer results in a power output 10+% less than you would ordinarily be capable of, then I'd suggest looking at making changes to your trainer set up. That may or may not include increasing the crank inertial load but often means paying attention to other factors such as having adequate cooling (very important) and use of motivational aids.

  • Once they get used to pedalling smoothly on low inertia trainers do they still benefit from a heavier flywheel? – Han-Lin Dec 11 '17 at 0:03
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    In terms of the science, the answer is no, changing crank inertial load has no effect of the capacity to sustain power, e.g.: ncbi.nlm.nih.gov/pubmed/17654231 ncbi.nlm.nih.gov/pubmed/16032416 ncbi.nlm.nih.gov/pubmed/8945654 – alexsimmons Dec 11 '17 at 3:30
  • CIL is not the only factor with such low inertia trainers, often it's the nature of the resistance provided that is the problem. – alexsimmons Dec 11 '17 at 3:33
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    @Han-Lin - maybe during acceleration intervals, but I don't think you would for steady spinning. I had a flywheel shatter on an older trainer, I still used it for years after, I guess my pedal stroke was smooth enough that I didn't really need it. – Marc Bernier Dec 13 '17 at 21:48
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    For acceleration training indoors you'd need a very high inertia trainer to begin to replicate the inertial load of the mass of a cyclist, e.g. I had one with a 30kg flywheel with a diameter of ~ 60cm and with double reduction gearing. That's starts to approach real life inertial loads. In general, accelerations, sprint and neuromuscular power training sucks on indoor trainers, best left to outdoor or the track. – alexsimmons Dec 14 '17 at 23:42
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I think you might be thinking of resistance rather than flywheel. The flywheel will smooth your pedal stroke and provide some resistance (inertia) when you are accelerating.

However, when spinning at a constant tempo, the flywheel is not playing much of a role. It's the resistance (fluid, magnet or fan) that's pushing against your stroke. Its the guy who's going to make you a better rider.

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