Stroke power or distance per stroke

[shanew]

Hello folks,

I am rather new to indoor rowing and have a data question. I understand that stroke efficiency is developed by keeping the stroke rate on the low side and increasing power. Thus the stroke power index (power in watts/spm) or the distance per stroke should go up as the stroke power improves. However, my previous two workouts seem contradictory.

Yesterday I rowed 50 minutes for 9816 metres at spm 19. That gives a pace of 2:33, avg watts of 98 a stroke power index of 5.16 and a distance per stroke (dps) of 10.33. Today I rowed 60 minutes for 12,022 metres at a pace of 2:30 at an spm of 20. That gives an avg power of 104 watts, a stroke power index of 5.21 and a dps of 10.02.

My question, between yesterday and today, I rowed with more power thus an increased spi but my dps fell. I thought spi and dps expressed the same thing? If not, which of these two rows was more efficient?

Thanks.

[Celtic]

Shanew,
I don't have the answer for you but I too am new to indoor rowing and would like to hear the answer from the experts on the forum. What you are getting for the dps result seems counter-intuitive to me too.

[ArmandoChavezUNC]

distance is linear, watts/power is not

[Carl Watts]

My advice is don't get too hung up on the data and numbers.

For the longer training rows your rating is good and aim for a DPS in the double digits and above. You still need more power per stroke and the pace will improve as well as the DPS.

You have not included and information about yourself in terms of age and weight, heartrate etc so it's not really possible to evaluate the results from a performance perspective.

Forget about SPI.

[Dickie]

My advice is don't get too hung up on the data and numbers.

For the longer training rows your rating is good and aim for a DPS in the double digits and above. You still need more power per stroke and the pace will improve as well as the DPS.

You have not included and information about yourself in terms of age and weight, heartrate etc so it's not really possible to evaluate the results from a performance perspective.

Forget about SPI.

I agree with Carl, but if you are intent on getting hung up with numbers, try this site - The Physics of Ergometers http://www.atm.ox.ac.uk/rowing/physics/ergometer.html

and forget about SPI

Fred Dickie
57 yrs, 233 lbs, 5' 9"
5k -19:08, 30 min - 7707 m, 20,050,000+ meters and counting

[RBFC]

As you row at a higher rate (19 vs. 20), you will spend slightly less time in the "glide" portion of the stroke. In other words, you're starting your next stroke a bit quicker. Both your power and time improved, so those are positive indicators in my opinion.

Lee

[jamesg]

Distance per stroke is useful if you don't change the rating much. This is because, in low speed aerodynamics and hydrodynamics, speed is linked to the cube root of Watts, so non-linear with power - twice as much Power only makes us go about 26% "faster". The erg math mimics this.

If you do want to compare strokes at widely different ratings, you'll have to use Watts/Rating. This = Work and is what we actually did in a single stroke. SPI is a misnomer, it's an index of work, or rather IS the work done in the stroke.

More useful than any number is of course - sweat. Not related to height, age, sex or anything else, only to what we've actually been up to. Very effective trainingwise too.

[kayakr]

Do workouts with intervals and "power 20's" and other more higher paced work should help increase your strength and stroke quality.

I started about where you were last winter and am now doing long steady state UT2 (~140 BPM hr) at 20-16 SPM at about 2:08-2:10, pace limited by heart rate considerations not stroke power. For intervals I'm doing 8x500m at 1:51 27-28 SPM with rest sufficient to drop heart rate to 110bpm (full recovery).

[Bob S.]

Do workouts with intervals and "power 20's" and other more higher paced work should help increase your strength and stroke quality.

I started about where you were last winter and am now doing long steady state UT2 (~140 BPM hr) at 20-16 SPM at about 2:08-2:10, pace limited by heart rate considerations not stroke power. For intervals I'm doing 8x500m at 1:51 27-28 SPM with rest sufficient to drop heart rate to 110bpm (full recovery).

27-28 spm is quite a low rate for 500m and I don't think that it makes any difference that it is a set of intervals and not a one time
500m.

Bob S. (low rate advocate, but not for the shorter pieces)

[kayakr]

re: 27-28 spm is quite a low rate for 500m.

Yeah, but I'm 185lbs, running strapless, and compared to most of you relatively slow.
I can feel that below 27 it becomes a struggle.

[NavigationHazard]

Yesterday I rowed 50 minutes for 9816 metres at spm 19. That gives a pace of 2:33, avg watts of 98 a stroke power index of 5.16 and a distance per stroke (dps) of 10.33. Today I rowed 60 minutes for 12,022 metres at a pace of 2:30 at an spm of 20. That gives an avg power of 104 watts, a stroke power index of 5.21 and a dps of 10.02.

My question, between yesterday and today, I rowed with more power thus an increased spi but my dps fell. I thought spi and dps expressed the same thing? If not, which of these two rows was more efficient?

Cheers, spi and dps don't express the same thing. One is watts/rating, the other meters/strokes. But as a general principle, you're right in thinking that an increase in one normally implies an increase in the other. Consider a 1' piece at 10 spi and a rating of 20 strokes/minute. That's an average of 200 watts. Since pace = 500* (1/((watts/2.8)^1/3), the wattage implies that you rowed at 2:00.5 pace/500m. You must have covered 249 meters, which works out to 12.45 . Now increase spi to 11 at the same rating of 20 spm. That's 220 watts, which is 1:56.7 pace, implicitly 257 meters in a minute and 12.85 meters/stroke.

However, there are a couple of things to keep in mind. One is that average watts for a piece is not necessarily the value implied by the average displayed pace. The reason has to do with the cubic value in the watts/pace relationship. Consider a 1000 meter piece at 20 strokes/minute at an average 2:00 pace (4:00 total elapsed time). That's 202.5 average watts, an spi of 10.13, and 12.5 meters/stroke. If you row the first 500m at 2:00 pace and the second 500m at 2:00 pace you'll see 202.5 watts on the monitor when you're done. But if your splits are uneven you may well see a different value. If you row the first 500m at 1:30 pace (480w) and the second at 2:30 pace (104w) your average watts are 484/2 = 241 watts even though you've still completed the 1k in 4:00. At a constant 20 strokes/minute, average spi in this case goes up to 12.05 while average distance per stroke stays exactly the same. Of course, rating won't stay constant given that kind of divergence from average. If you row the first 500m in 1:30 at 30 strokes a minute and the second 500 in 2:30 at 20 strokes a minute, you still average 241 watts for the whole 4:00 1k at an average rating of 23.4. Now your spi and dps results are 16.1 and 11.1 for the first 500 split; 5.2 and 10.0 for the second. Overall your spi for the 1k is now 10.30 while distance per stroke is now 10.53 meters/stroke. You've still rowed a 4:00 1k. Your spi has gone up from 10.13 at 20 spm to 10.30 at 23.4 spm. But your distance per stroke has gone down from 12.5 to 10.53.

If I haven't already lost you ... and my maths aren't screwed up .... It gets even more complicated when you start factoring monitor resolution/rounding/truncating (e.g. meters and watts and strokes/minute in whole units). Bottom line: IMO the two rows you did were roughly comparable in terms of effort on a per stroke basis. Bear in mind that the second one was 10' longer than the first, and thus required more grunt overall. I think what you're seeing as far as spi going up slightly but dps going down slightly is probably an artifact of slightly uneven pacing.

[Bob S.]

re: 27-28 spm is quite a low rate for 500m.

Yeah, but I'm 185lbs, running strapless, and compared to most of you relatively slow.
I can feel that below 27 it becomes a struggle.

Strapless would definitely make a difference, of course. Nowadays, I use the dynamic, so I can get away with going strapless for just about any rate, However, on my previous model, a D, I always strapped in if I had any anticipation of getting the rate up over 30 - especially when it was not on slides.

Was there some special reason for doing 500s strapless? I don't see that the 185lbs would make any difference in your ability to up the rate. Nor should relative slowness. In my own case, I would be unlikely to do even one 500m at a pace of 1:51, let alone 8, but there is no problem getting the rate up to 40 for a short piece. (On the dynamic, 60spm is within range - 45 or so on a D on slides.)

Bob S.

[kayakr]

I could take the rate up, but why?
I'm sure going for a BP 500 I'd need to take the same rate up to 35 or something.

[Bob S.]

I could take the rate up, but why?
I'm sure going for a BP 500 I'd need to take the same rate up to 35 or something.

Yeah, I see your point. I guess that it depends on the purpose of doing 8X500m intervals. I usually think of them as high rate practice, but I don't really know what their main training purpose is. Something about improving strength, but lower rates would be appropriate for that.

Bob S.

[kayakr]

re: Purpose of 500m
I don't really care about boat training, I'm focused on the strength, aerobic and anerobic effects. Lower SPM's seem to be a more efficient stroke in terms of quality of catch, stroke length, flywheel is slowing down, etc.

1 to 2 minute intervals basically all with equal or greater recovery are good for max power output and also training to recover smartly. e.g. VO2 max according to what I've read. My HR goes from 110 (full recovery) to 165-170 by the end of the interval. This is similar to my mountain biking, where we have short (100-200 vertical) steep hills where my HR goes from typical "cruise" of 130-140 to 160-170. On longer hills I'm trying to use low gears to spin and to avoid HR > 90% but it can be difficult because climbing is a full body sport at maximum gradients.

The intervals have helped me prepare for MTB where this year I'm not as burned out after a session. Last year before becoming HR aware my performance was decreasing session to session probably because of overdoing it with HR on the high end, as well as limited weekday preparation. And I frequently would crash on the couch (asleep) afterwards. Now I feel I could "do it again" after a session. Although if I did I would need to sleep then