Constant power training question?

nmcgann said:

The turbo reduces the resistance applied to the back wheel as cadence increases as it assumes that the rider is using more power to spin the increased cadence. Neil

Can you give us a little more information about your trainer (turbo)?
Is is magnetic, fluid, or wind resistance? Is the resistance changeable via a computer control or knob?

nmcgann said:

Sorry in advance if this is a dopey question....

Nonsense. Don't be a dope... :p

nmcgann said:

I've recently started power training on a turbo and I find that when I am doing long efforts at the upper end of my capability in "constant power" mode I seem to naturally increase my cadence to reduce the resistance I feel (up from 95rpm-ish to 105rpm+). The turbo reduces the resistance applied to the back wheel as cadence increases as it assumes that the rider is using more power to spin the increased cadence. This is a bit unnatural as out on the road increasing cadence increases perceived resistance unless changing down through the gears.

Power is defined as resistance times speed. If the speed goes up, the resistance naturally goes down, and vice versa. In 'constant power' mode, as you start to increase cadence without changing gears, the rear wheel spins faster and the trainer has to reduce the resistance to keep power constant.

There's nothing right or wrong about it, just pedal at the cadence you're comfortable with and the trainer will adjust resistance to dial-in the power you asked for.

Pureshot78 said:

Can you give us a little more information about your trainer (turbo)?
Is is magnetic, fluid, or wind resistance? Is the resistance changeable via a computer control or knob?

It's a Tacx Flow. It's not a trainer-specific thing though - I'm away from home on a business trip at the moment and the hotel's gym bikes do exactly the same in constant power mode (your weight is one of the parameters in the program - presumably there is a formula to estimate power loss vs cadence based on body weight that is then used by the trainer to calculate the resistance to apply).

Neil

frenchyge said:

Nonsense. Don't be a dope... :p

Power is defined as resistance times speed. If the speed goes up, the resistance naturally goes down, and vice versa. In 'constant power' mode, as you start to increase cadence without changing gears, the rear wheel spins faster and the trainer has to reduce the resistance to keep power constant.

There's nothing right or wrong about it, just pedal at the cadence you're comfortable with and the trainer will adjust resistance to dial-in the power you asked for.

Sorry, I didn't explain very well - I understand how power is defined. It's the bit that includes bodyweight in the constant power calculation I'm unclear about.

But is it generally likely that I would gain more training benefit if I use a lower cadence (e.g. 95 - a more natural road cadence for me) with the resulting higher resistance?

Neil

nmcgann said:

Sorry, I didn't explain very well - I understand how power is defined. It's the bit that includes bodyweight in the constant power calculation I'm unclear about.

Bodyweight does not factor into the power formula on a stationary bike. The bike is sensing the speed of the rear wheel and applying the necessary resistance to achieve the power you set. No magic formulae, the trainer is just doing what you told it -- keeping power constant without regard for speed.

nmcgann said:

But is it generally likely that I would gain more training benefit if I use a lower cadence (e.g. 95 - a more natural road cadence for me) with the resulting higher resistance?

There's no more training benefit. Since the training benefits are mostly metabolic in nature, watts are watts regardless of cadence. Just pedal at your natural cadence.

frenchyge said:

Bodyweight does not factor into the power formula on a stationary bike. The bike is sensing the speed of the rear wheel and applying the necessary resistance to achieve the power you set. No magic formulae, the trainer is just doing what you told it -- keeping power constant without regard for speed.

There's no more training benefit. Since the training benefits are mostly metabolic in nature, watts are watts regardless of cadence. Just pedal at your natural cadence.

Oh. I presume the body weight bit is for calorie calculation then?

Good to hear that the training benefit is the same - it appears that I naturally spin faster to output my higher power range. That is good as I have proved to myself that I am much less tired on long rides (100miles+) when I spin fast.

Neil

nmcgann said:

It's a Tacx Flow. It's not a trainer-specific thing though - I'm away from home on a business trip at the moment and the hotel's gym bikes do exactly the same in constant power mode (your weight is one of the parameters in the program - presumably there is a formula to estimate power loss vs cadence based on body weight that is then used by the trainer to calculate the resistance to apply).

Neil

I have the same experience with the Flow, but I suspect it ain't that reliable. I beleive that it cant "keep up" when you raise your cadence in ergo mode, - I think that it miscalculate the actual power at higher cadences (showing higher numder than it really is).

OTOH it is quite normal to raise your cadence when you raise your power, I feel like I'm primarily trying to keep the same torque, not the cadence, when I raise the power.

Doublebiker said:

I have the same experience with the Flow, but I suspect it ain't that reliable. I beleive that it cant "keep up" when you raise your cadence in ergo mode, - I think that it miscalculate the actual power at higher cadences (showing higher numder than it really is).

I confirm that it does. And not only that, but as the bike wheel speed increases (no matter if it's as a result of increased cadence or simply changing bike gear) the power numbers become even more overestimated.

nmcgann said:

I'm wondering if this increase in cadence is a good idea as it is actually reducing the power available to move the bike (more power lost in high cadence) so prolonged training on the turbo might be adapting my technique to produce less real power on the road than could be possible.

At a given power level (say 200w), riding at a cadence that is significantly higher than self-selected comfortable cadence seems to raise one's metabolical cost of doing the exercise. Really I have no idea about the potential of this "drill" on one's fitness level. Something is happening, but how usefull adaptation to it is(?), I am not sure.

I intend to practice it this year, during some L2-3 workouts, or during sprint work. My comfort zone is between 85 and 95rpm. I will work on maintaining 95-100 during some 'aerobic' workouts, and higher during sprint.

SolarEnergy said:

At a given power level (say 200w), riding at a cadence that is significantly higher than self-selected comfortable cadence seems to raise one's metabolical cost of doing the exercise. Really I have no idea about the potential of this "drill" on one's fitness level. Something is happening, but how usefull adaptation to it is(?), I am not sure.

I intend to practice it this year, during some L2-3 workouts, or during sprint work. My comfort zone is between 85 and 95rpm. I will work on maintaining 95-100 during some 'aerobic' workouts, and higher during sprint.

I predict that this will raise your "comfort zone", but won't enable you to generate any more power than you already can.