Erg wattage vs Cycling wattage

[jamesg]

force to decelerate a moving mass. Where does that force come from?

From hips, arms and shoulders acting on the handle and doing work; unless you use the feet. We're not attached to the erg anywhere else.

[Nomath]

force to decelerate a moving mass. Where does that force come from?

From hips, arms and shoulders acting on the handle and doing work; unless you use the feet. We're not attached to the erg anywhere else.

Exactly!
So the kinetic energy of the moving body mass is used to drive the flywheel. It is not lost.

[Carl Watts]

force to decelerate a moving mass. Where does that force come from?

From hips, arms and shoulders acting on the handle and doing work; unless you use the feet. We're not attached to the erg anywhere else.

Exactly!
So the kinetic energy of the moving body mass is used to drive the flywheel. It is not lost.

Wow I'm lost for words.

So if you put 100Kg on wheels and push it up a slight incline with an acceleration of 2m/sec it takes absolutely no power to do that ?

The power to move your body is lost on both the drive and the catch. There is also power lost in the shock cord as at best 80% of it is returned to you in the catch. The rest is similar to a bike you have a few bearings and a chain so the losses there will be similar.

You have to make up that additional power loss on the Erg because it never makes it to the flywheel. Depending on rating and pace you need to add 30% +/- to the Erg power to equal that of the cycling power. Just the fact you have to move your whole body almost continuously would be a very large percentage of that loss.

The difference would show up immediately by just using your heartrate on the bike and the rower. 30% would be a good starting point for say a steady state 30 minute. The losses will go up significantly with rating. The actual percentage compensation curve would be really quite complex to get there with some accuracy it would take into account a number of variables from your weight to your rating. This data is in ErgData like slide speed but even if it was done successfully its still subject to cheating, instead of lying about your weight on the bike by making it low you lie about your weight on the Erg by making it high because the losses are higher in absolute Watts the heavier you are. Your weight would have to link through from the Calc into Zwift to help offset that or people would be putting in 150Kg to get that power loss figure boosted.

Good luck in explaining why your HR is higher on the Erg than on the bike for the same power otherwise. A percentage is biomechanical efficiency but the biggest chunk is pure loss moving the bodyweight.

Anyway its kind of pointless debating exactly what it should be other than for interest sake because you can currently choose to Boost 30%, 40% or even 50% using RowedBiker in Zwift

[Nomath]

Wow I'm lost for words.

So if you put 100Kg on wheels and push it up a slight incline with an acceleration of 2m/sec it takes absolutely no power to do that ?

Carl, I don't want to be pedantic, but as much as I appreciate you technical know how, your knowledge of the physics is below par.

First, the units of acceleration are not m/sec, but m/sec². This may seem like a slight error, possibly a typo, but it's not! The best way to realize what an acceleration of 2 m/sec² means is to write it as 2 m/sec per sec. So if you start at speed=0, after 1 sec the speed is 2 m/sec, after 2 sec the speed is 4 m/sec, after 3 sec the speed is 6 m/sec, etc.
But in rowing the initial acceleration at the catch is not 2 m/sec², but roughly 6 m/sec² for recreational rowers and above 10 m/sec² for elite rowers. So an elite rower attains already a speed of 2 m/sec after 0.2 sec. Since the slide is only about 1.2 m long, we have to decelerate about halfway the slide. As Newton's laws imply, you need a braking force to decelerate. As jamesg explained, this braking comes from pulling hard on the handle.
So whether you believe it or not, the kinetic energy of your 80 kg body (legs don't move at the same speed) attained after the catch, is fully recovered when your drive has come to a standstill.

The kinetic energy of body movement in the recovery is different. It is not obviously recovered, although there are some theories about elastic compression just before the catch. This loss may explain your increased HR on an RowErg compared to cycling and is part of the estimated 10-20% power difference.

[JaapvanE]

Good luck in explaining why your HR is higher on the Erg than on the bike for the same power otherwise. A percentage is biomechanical efficiency but the biggest chunk is pure loss moving the bodyweight.

Rowing has a different characteristic on the flywheel: where cycling keeps it more or less constant, in rowing it spins up and down. For flywheels (and boats) a constant speed is much more efficient than speeding up and slowing down, even if the average remains the same. This is because the dragforce increases with speed, thus at higher speeds you lose more energy due to drag. Such inefficiency might explain a lot for effort you have to make decent speeds.

[jamesg]

So the kinetic energy of the moving body mass is used to drive the flywheel. It is not lost.

It may not be lost, but this does not mean it can be used. To stop and go back the other way requires work by muscle, since we have no change in height or stored elastic energy to use.

Many have tested your fallacy by jumping out of a window. It doesn't work, we don't bounce back unless there's something elastic to bounce off.

[JaapvanE]

It may not be lost, but this does not mean it can be used. To stop and go back the other way requires work by muscle, since we have no change in height or stored elastic energy to use.

Eeehm,

There is a subtle change of height, as the rail has a slight tilt, storing some potential energy. As someone who rows 50% strapless, that is almost all you can use (along with moving your weight) as there is no muscle capable of pulling yourself in. Timing is everything here: start your drive too explosively and you fall off at the other end as my arms aren't capable of producing the force to decelerate 100 kilo going one way.

[jamesg]

Sure, as also the bungee serving to retract the chain. Both can and do absorb and release some energy, and make it possible to use the erg.

[Nomath]

It may not be lost, but this does not mean it can be used. ...

Your drive comes to a stop because you pull the handle and the handle offers resistance. These pulls are driving the flywheel.
It's no fallacy.

[jamesg]

1 So the kinetic energy of the moving body mass is used to drive the flywheel. It is not lost.
2 Your drive comes to a stop because you pull the handle and the handle offers resistance

I choose the second as a description of what happens.

[JaapvanE]

1 So the kinetic energy of the moving body mass is used to drive the flywheel. It is not lost.
2 Your drive comes to a stop because you pull the handle and the handle offers resistance

I choose the second as a description of what happens.

Aren't they the same thing?

[Carl Watts]

1 So the kinetic energy of the moving body mass is used to drive the flywheel. It is not lost.
2 Your drive comes to a stop because you pull the handle and the handle offers resistance

I choose the second as a description of what happens.

Aren't they the same thing?

They are both wrong anyway.

[JaapvanE]

They are both wrong anyway.

Could you elaborate on why you think that? Apart from the slight incline and some air resistance, I can't see a force from stopping me from falling off the rail when rowing strapless....

[Tsnor]

They are both wrong anyway.

Nice. Made me laugh.

Without picking up the handle you can row back and forth and work up a sweat, so there is energy being used. It's not like a spring or a pendulum. It's more like Lotus active suspension.

It is not free to stop at the end of the slide and start back the other way. You apply the energy to the handle to stop at the end of the slide, but you gotta create that energy. The energy you apply to the handle is not coming from your motion towards the end of the slide. Not all the energy applied to the handle goes into the flywheel, some is used to stop your motion. And the energy applied to the handle is only about 20% (or whatever rowing efficiency you want to put in) of the energy you spent. That's why C2 projects about 5X more cal/sec than implied by reported watts.

[JaapvanE]

I agree with you that moving X kilo's up and down a very frictionless slide still consumes some energy.

I think/assume that during the transition from legs to the back still some kinetic energy is transferred from my moving body to the flywheel and make it decelerate: i.e. I am decelerating and when rowing strapless, it can't be because my legs excert some negative force (by hanging on my hamstrings).