Relationship between split time and stroke rate

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Ombrax
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Re: Relationship between split time and stroke rate

Post by Ombrax » November 20th, 2020, 3:19 am

JotaBg wrote:
November 19th, 2020, 4:19 pm
Thanks both

Sorry for not using the right units, I have a weak background in physics :roll:

So, as a conclusion, my understanding is that a similar force per stroke will produce a higher power (per stroke) readout at a higher stroke rate

I tried it this morning. A few strokes at a 20 spm applying a certain force and a few strokes applying more or less the same force but in this case at a 12 spm approx. Even though I applied a similar force, the wattage per stroke was much lower when the spm were reduced. Does this make sense?
Just out of curiosity, what exactly are you trying to figure out?

Remember, as was stated above (and sticking with translation instead of rotation, because it's easier to understand)

Work = Force x Distance
Power = Work / unit time

That and the knowledge that we're force-limited (which is one of the reasons we ramp up stroke rate to get to a higher pace - the force our muscles can put out is limited, so we tax our cardio vascular system more by using a limited force more often to compensate - just like revving a smaller engine to higher RPMs to get to higher horsepower) is really all you need to worry about when it comes to understanding the physics part of going faster on the rower.

Continuing the engine analogy: Horsepower = Torque x RPM / 5,252 (where TQ is Ft-lbs)
Assuming the Torque curve is flat, if you can double the RPM you'll double the HP.

Same idea on the erg, with stroke rate instead of RPM.

JotaBg
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Re: Relationship between split time and stroke rate

Post by JotaBg » November 20th, 2020, 3:44 am

Ombrax wrote:
November 20th, 2020, 3:19 am

Just out of curiosity, what exactly are you trying to figure out?

Remember, as was stated above (and sticking with translation instead of rotation, because it's easier to understand)

Work = Force x Distance
Power = Work / unit time

That and the knowledge that we're force-limited (which is one of the reasons we ramp up stroke rate to get to a higher pace - the force our muscles can put out is limited, so we tax our cardio vascular system more by using a limited force more often to compensate - just like revving a smaller engine to higher RPMs to get to higher horsepower) is really all you need to worry about when it comes to understanding the physics part of going faster on the rower.

Continuing the engine analogy: Horsepower = Torque x RPM / 5,252 (where TQ is Ft-lbs)
Assuming the Torque curve is flat, if you can double the RPM you'll double the HP.

Same idea on the erg, with stroke rate instead of RPM.
Thanks, Ombrax. This makes sense to me and it's precisely what I'm trying to figure out. What you explained is spot on the conclusion that I arrived at.

However, other posters have said that the Power readout of the machine does not change regardless of the SPM/RPM. And this is when I get confused. Do you understand what I mean? It's the disconnection between the statement that the Power (in Watts) readout of the machine does not change regardless of my SPM and your example, that a higher rate produces more power

jamesg
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Re: Relationship between split time and stroke rate

Post by jamesg » November 20th, 2020, 4:11 am

I shouldn't worry about it. In rowing there are three engineering elements:

1 Stroke Length
2 Handle Force
3 Rating (spm).
And one essential: style, which is what lets us put it all together.

These three, multiplied together in the right units, = Watts.

Based on your height some numbers can be suggested, and seen in ergdata if you use it:
Stroke length = 70% of height; but say 1.2m
Average Handle force = half your fit weight; 40 kg will do as an example.
Rating 20

With these three numbers you'll produce 40g x 20/60 x 1.2 Watts = 157 W, enough to get you fit.
08-1940, 183cm, 84kg. Last seen MHR 155, in 2k (2020-12-03) 8.47.6@23

JotaBg
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Re: Relationship between split time and stroke rate

Post by JotaBg » November 20th, 2020, 4:31 am

jamesg wrote:
November 20th, 2020, 4:11 am
I shouldn't worry about it. In rowing there are three engineering elements:

1 Stroke Length
2 Handle Force
3 Rating (spm).
And one essential: style, which is what lets us put it all together.

These three, multiplied together in the right units, = Watts.

Based on your height some numbers can be suggested, and seen in ergdata if you use it:
Stroke length = 70% of height; but say 1.2m
Average Handle force = half your fit weight; 40 kg will do as an example.
Rating 20

With these three numbers you'll produce 40g x 20/60 x 1.2 Watts = 157 W, enough to get you fit.
Thanks again, jamesg. This makes sense and confirms my understanding.

I quickly repeated my experiment and having a higher spm (35-40) and producing much less force at the handle still gives more watts than a much lower spm (15-20) and producing more force at the handle, so definitely Power is spm dependent, as confirmed by your explanation.

Many thanks, now all my questions are answered,
J

Allan Olesen
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Re: Relationship between split time and stroke rate

Post by Allan Olesen » November 20th, 2020, 5:11 pm

JotaBg wrote:
November 20th, 2020, 3:44 am
However, other posters have said that the Power readout of the machine does not change regardless of the SPM/RPM. And this is when I get confused.
If you keep a constant energy per stroke, and you increase the stroke rate, your power will increase. There should be no doubt about that.

I have a feeling that some people refuse to accept the concept of energy per stroke, and consequently they give some quite confusing answers.

(And for what it is worth: Power and energy calculations is my dayjob. I am a mechanical engineer.)

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Re: Relationship between split time and stroke rate

Post by JotaBg » November 20th, 2020, 6:16 pm

Allan Olesen wrote:
November 20th, 2020, 5:11 pm
If you keep a constant energy per stroke, and you increase the stroke rate, your power will increase. There should be no doubt about that.

I have a feeling that some people refuse to accept the concept of energy per stroke, and consequently they give some quite confusing answers.

(And for what it is worth: Power and energy calculations is my dayjob. I am a mechanical engineer.)
Many thanks for the further clarification and taking the time to respond, Allan! I appreciate it.

I have ended up learning quite a few things with this discussion and it’s clear now. Sometimes not having a straightforward answer ends up stimulating the curiosity even more, so it was definitely worth it. Thanks everyone.

Dangerscouse
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Re: Relationship between split time and stroke rate

Post by Dangerscouse » November 21st, 2020, 9:17 am

JotaBg wrote:
November 20th, 2020, 6:16 pm
I have ended up learning quite a few things with this discussion and it’s clear now. Sometimes not having a straightforward answer ends up stimulating the curiosity even more, so it was definitely worth it. Thanks everyone.
Same here, I dont think too much about the physics of it all.
47 HWT; 6' 4"; 1k= 3:09; 2k= 6:36; 5k= 17:24; 6k= 21:09; 10k= 35:46 30mins= 8,428m 60mins= 16,461m HM= 1:16.47; FM= 2:44:04; 50k= 3:16:09; 100k= 7:52:44; 12hrs = 153km

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jackarabit
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Re: Relationship between split time and stroke rate

Post by jackarabit » November 21st, 2020, 6:58 pm

Zipjuice per impulse is amplitude.
Iterations per unit of time is frequency.

More coal and
More steam and
More turns
Means first on the scene!
There are two types of people in this world: Those who can extrapolate from incomplete data

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jamesg
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Re: Relationship between split time and stroke rate

Post by jamesg » November 22nd, 2020, 4:54 am

Didn't know you're a tug skipper!
08-1940, 183cm, 84kg. Last seen MHR 155, in 2k (2020-12-03) 8.47.6@23

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jackarabit
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Re: Relationship between split time and stroke rate

Post by jackarabit » November 22nd, 2020, 1:24 pm

jamesg wrote:
November 22nd, 2020, 4:54 am
Didn't know you're a tug skipper!
Nor a Gravesend waterman neither but I know how to splice the occasional jingle. :wink:
There are two types of people in this world: Those who can extrapolate from incomplete data

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