Watts and handle force not making sense to me

[Bobpond]

I am looking at information from ErgData and the PM5 and I'm a bit confused. I'm concerned maybe something is wrong with my new Model D.

Ave. Force was reading about 40kg consistently. I was rowing at 20SPM. Drive length 1M. Watts were only 100.

(6x100)/20 = 30 so where are those other 10kg going? I may have varied a little over 30 minutes, but no way I was below 30kg of handle force.

Is there anything I can check or some other measurement either in ErgData or on the PM to see if there is an issue?

Maybe there could be something in my technique causing this?

I also did a final 500 pulling so hard at 30SPM that the front of the rower was jumping off of the floor and could only get to 150W with over 1M stroke length.

I would appreciate any insight on this.
Bob

[jamesg]

Is 1m the distance your handle travels overall, or the part of the stroke under load? There is some slack at the catch before the freewheel engages; this is likely about 30 cm.

Also, is 40 kg peak or average force? The force curve during the stroke is sinusoidal, so average force is roughly Peak/Root 2, i.e around 70% of peak.

Taking average force as 40 kg (which means your peak force would be almost 60 kg), we have 40 kg x 1m x g x 20/60 = 131 W, but if the net length is 70 cm, we have 70% of this, 101 W.

The piece at 30 would likely be even shorter stroke: 50kg x 0.7m x g x 30/60 = 172 W: 50 kg average implies 70kg peak force.


If the front feet (under the flywheel) jump off the floor at rate 30, you must be pulling yourself forward very hard with your straps but have a very slow stroke; so you undoubtedly have some technique problems. First thing to do would be to set the damper to zero, then pull long and quick, with a slow sequenced recovery. Problems on the erg are, always, either not a problem at all or technique.

In the end all we need do is calculate our fit/thin weight in kg and then aim to pull twice as many Watts at low rating and long times, adjusted for age and sex.

[Bobpond]

Thanks James.

I am using the display from ErgData that says Drive Length and trying to keep it at 1M or higher. I am using the field that says Ave. Force for handle force.

If Drive Length is not taking into account the slack,or more likely I missed it in my calculation, then there's my confusion. Sorry for being dense but what does "g" refer to in the calculation?

I row strapless, when I was pulling at 30 as hard as I could it was during the drive that the front end was coming up. I was thinking about being light on the seat and probably lifting up too much. I'm really not good enough yet for that rate or effort it was a bad idea.

Funny last night I did exactly what you said, I dropped the damper to 0 and concentrated on stroke length. I went almost as far in 30 minutes as my best but with less effort. I generally think of the drive and recovery as a waltz so I think the ratio is pretty good.

A month ago I could only manage about 75W for 30 minutes without my heart rate going over 160, now I can do 100 with that effort. I have a long way to go. I need to get to 166.

Thanks again,
Bob

[Bob S.]

g: conversion factor for units of weight to units of force, about 9.80N/kW?

B.

[Bobpond]

Thanks for the definition Bob.