Concept2 Forum

How does the C2 convert rowing efficiency to distance when everyone's efficiency is different? Will the C2 display the same distance traveled for two people taking the same number of strokes?

It's not using a stroke count to calculate distance.

It's using flywheel inertia and acceleration to measure the energy expended by the rower on the seat pulling the handle (more correctly pushing against the ergo with their legs).

The whole process is documented in exquisite detail at: http://eodg.atm.ox.ac.uk/user/dudhia/ro ... meter.html

Its the great thing about the Concept 2 Erg. The way it does the math makes your result directly comparable to others, even if they use a different Concept 2 rower.

No, stroke rate isn't going to determine distance as anybody's stroke rate can be a lot more powerful (or weaker) than someone else's even when maintaining exactly the same strokes per minute.

For example I did a 10k at r20 tonight and I rowed at 1:57 average pace but I could have rowed this distance, albeit with a lot more effort, also at r20 and an average of 1:52. Some really strong rowers that I know can row shorter distances at 1:39/40 pace at r20

happycamper515 wrote: ↑

January 24th, 2020, 1:32 am

... Will the C2 display the same distance traveled for two people taking the same number of strokes?

No, but surprisingly the C2 displays roughly the same distance for one person taking the same number of strokes, no matter the applied power !

I have rowed on the C2-erg for about 15 years now and due to age my best average 500m split time on the 5K has increased from about 1:58 to 2:08. But I always count my strokes and 100 strokes add about 1000 meters (±30 m).
Last year I did a lazy 5K where the average 500m split was 2:22 and it took me about 500 strokes. An all-out 5K run had an average split of 2:04 and also required 500 strokes.

Of course, this depends on the length of the stroke. For me, it starts as far forward as possible (bar touching metal) and ends with legs fully stretched, body about 20° leaning backward and bar touching breast. Another person with longer legs will probably do more than 10 meter per stroke. That's why two people taking the same number of strokes may have different distances traveled.

If you look at the physics in http://eodg.atm.ox.ac.uk/user/dudhia/ro ... meter.html, this is not obvious at all !!

Sorry @Nomath that makes no sense to me and doesn't match my experience. I regularly do a slow 1k as a warm down at 20 spm...the last one shows as 86 strokes over 4:22.2. My best this year for a 1k is a 3:15.8 but at a much higher stroke rate (37) and totalling 123 strokes. There is no interpretation of 86 and 123 which could be taken as "more or less the same" to cover 1k. Looked at the other way as you did - ie distance per stroke - the figures are no closer. I can only assume I've misunderstood your post....

MPx wrote: ↑

January 24th, 2020, 7:09 pm

Sorry @Nomath that makes no sense to me and doesn't match my experience. I regularly do a slow 1k as a warm down at 20 spm...the last one shows as 86 strokes over 4:22.2. My best this year for a 1k is a 3:15.8 but at a much higher stroke rate (37) and totalling 123 strokes. There is no interpretation of 86 and 123 which could be taken as "more or less the same" to cover 1k. Looked at the other way as you did - ie distance per stroke - the figures are no closer. I can only assume I've misunderstood your post....

Not sure if I understood fully either, but there is the ideal of training a strong stroke at low rate and then using that same stroke at higher and higher rates to get faster. As I understand it, that more or less has to be done OTW to actually stay afloat (I've never been in a boat, so no authority there!). If you're using the same stroke, then the work done per stroke would be the same, but the average power (and so speed) would be much higher at higher rates.

In practice, we all shorten our stroke at higher rates to a greater or lesser extent, so this would breaks down anyway.

I regularly use this basic calculation to get a somewhat general sense of my rowing efficiency from workout to workout...

average watts / average stroke rate = SPI

I'll use tonight's session for an example... 5000m / 19:18.3 / 1:55.8 / DF 130 / SR 22 / SPI 10.22 / 225w

225w / 22 stroke per minute = Stroke Power Index of 10.22

This calculation is only valid if you maintain a consistent stroke rate from beginning to end.
Sprinting at the end will significantly skew the result!!!.

Anything over 10.0 is a good target. Elite rowers can regularly push the SPI over 15.0 (which is hard to do!)

How does the C2 convert rowing efficiency to distance

The PM measures the Work (= Force x Distance) we do on the erg handle during the pull; calculates and displays the power averaged over the entire stroke time; and from this derives a speed and a distance. The Power/Speed relationship is given by W=kV³, the cube law being typical of hydrodynamic drag.

Will the C2 display the same distance traveled for two people taking the same number of strokes?

Only if they pull strokes with the same amount of work done on the handle. Length and Force may differ singly, but their product, Work, must be the same if Power, speed and distance are to be the same.

Nomath wrote: ↑

January 24th, 2020, 6:32 pm

No, but surprisingly the C2 displays roughly the same distance for one person taking the same number of strokes, no matter the applied power !
....

Not for me, my MPS (meters per stroke) vary a lot. Some examples:

2,000m
6:58.9
Average Watts 305
Stroke Rate 20
Stroke Count 141
Drag Factor 125
MPS: 14,18

2,000m
6:43.9
Average Watts 340
Stroke Rate 32
Stroke Count 214
Drag Factor 135
MPS: 9,35

100m
0:14.4
Average Watts 938
Stroke Rate 58
Stroke Count 14
Drag Factor 210
MPS: 7,14

max_ratcliffe wrote: ↑

January 24th, 2020, 7:20 pm

Not sure if I understood fully either, but there is the ideal of training a strong stroke at low rate and then using that same stroke at higher and higher rates to get faster.

Yes Max. Dean (@bisqeet on here) was a very strong advocate of this approach. And it worked very well for him - although at the time he was doing an enormous milage with an HM distance or more on most days. Not sure its possible to adopt that approach with less input as maintaining stroke power at higher rates is very very hard unless extremely fit aerobically.

MPx wrote: ↑

January 24th, 2020, 7:09 pm

Sorry @Nomath that makes no sense to me and doesn't match my experience. I regularly do a slow 1k as a warm down at 20 spm...the last one shows as 86 strokes over 4:22.2. My best this year for a 1k is a 3:15.8 but at a much higher stroke rate (37) and totalling 123 strokes. There is no interpretation of 86 and 123 which could be taken as "more or less the same" to cover 1k. Looked at the other way as you did - ie distance per stroke - the figures are no closer. I can only assume I've misunderstood your post....

I'm with you on this Mike. The wattage per stroke is surely most important factor in distance travelled? I have seen a photo of Chris Scott (a very big and powerful rower) do a 2k in 6:13.3 @ r24. If tried to do a 2k at r24 I would get no way near (at a guess I'd be at least 70ish secs slower) but the length of stroke would be very similar as I'd be having to really maximise it and I think we are both the same height.

Of course, jamesg gave the right answer as to how the C2-erg works and calculates power, distance, etc.
But it's still interesting to wonder about the less obvious empirical facts.

MPx wrote: ↑

January 24th, 2020, 7:09 pm

Sorry @Nomath that makes no sense to me and doesn't match my experience. ....

This morning I did a 10K. I started deliberately at a very relaxed pace and gradually increased my effort so that I ended at 95% of my HR-max (about 160 bpm). The HR graph below is from my Polar M460. The start of the rowing was 1 min after start of the Polar record.
Because the PM3 saves only rounded numbers for stroke rates, which is rather imprecise, I did a stroke count in every 2K lap. The T500 and the power (W) is the average for the 2K lap, but the Heart Rate (bpm) was saved at the end of each lap.
Results
0-2K : 565.9 sec - 119 bpm - 2:21.4 - 124W - 208 strokes - 22.1 spm
2K-4K : 559.6 sec - 127 bpm - 2:19.9 - 128W - 203 strokes - 21.7 spm
4K-6K : 550.5 sec - 133 bpm - 2:17.6 - 134W - 199 strokes - 21.7 spm
6K-8K : 539.5 sec - 141 bpm - 2:14.8 - 143W - 195 strokes - 21.7 spm
8K-10K : 521.9 sec - 150 bpm - 2:10.4 - 158W - 200 strokes - 23.0 spm

The data show that each stroke covers about 10 meters (±4%). There is a weak trend that the distance increases with more power, but this trend reverses as the stroke rate goes up.

Years ago one of Paul's Laws said pull 10m every stroke. It served to change the approach of the beginners who here reported rowing at 35 but slow pace.

He also invented the stroke power index, which by using Watts lets us maintain almost constant the Work in the stroke, whatever the rating; effectively using rating to control training bands.