Stroke Rate and Perceived effort

[gregsmith01748]

Hi,

I "know" from doing low rate workouts that achieving the same split (that is the same power) is harder and harder as the stroke rate decreases.

Does anyone out there have any data to substantiate the relationship?

For example, I did a HM today with a pace of 2:03 and a stroke rate limit of 20. My heart rate was up to 168 by the time I finished. Other times, I have done HMs at a sub 2:00 pace, but at a stroke rate of 23 to 26, my heart was lower.

I'm just wondering if there is a way to figure out the "inefficiency" of lower stroke rates?

Thanks

[sander]

It could differ very much from person to person. At the lower stroke rates, the flywheel slows down more during the return phase. This means you are driving your legs down at a slower speed. To achieve the same average power, you have to exert more force. This might be less efficient for you. Every muscle group has an optimum speed at which it can deliver it's maximum power. On the other hand, it might feel heavier but not actually be.

[gregsmith01748]

I'm surprised that you don't think there is some kind of real (ie physics based) relationship. Given that you are using a consistent drag factor for both cases, if you row at low rates, the speed of the fly wheel varies more widely, than if you row at a higher rate, basically, the wheel spends more time slowing down and less time speeding up. If force is related to acceleration (squared), i would have thought that greater avg force is required to maintain the same avg fly wheel rotational velocity.

I guess I need to go back to that 'physics of ergometers' paper and try to figure this out.

[KevJGK]

Just for starters - this chart shows that the relationship between the mythical ‘power per stroke’ value isn’t linear for a constant pace. This is 02:03 pace (188.1 watts) from 30 down to 10 spm.

[jamesg]

I "know" from doing low rate workouts that achieving the same split (that is the same power) is harder and harder as the stroke rate decreases.

To achieve the same average power, you have to exert more force. This might be less efficient for you. Every muscle group has an optimum speed at which it can deliver it's maximum power.

This IS a physics based answer.

On the erg we can adjust drag, rating and stroke length (which can be summed up as giving a certain impedance) to enable maximum power transfer to the handle. Power transfer is most efficient when our own impedance equals that of the machine. So if you want to transfer the SAME power (and so see the same pace), but at another impedance, you have to do more work, which is exactly what you saw.

This is why technique is so important: learning to row "well" means using our best combination of handle speed and force, drag, rating etc (i.e. impedance), so that we do least internal work (by muscle acting on bone) for the same external power delivered to the handle.

Beginners often start at very high drag, believing this makes them work harder. Which is possible, but they won't see it on screen. Other beginners start using very short strokes at high rating; this too can make them work hard, but again it doesn't show on screen. The cause in both cases is impedance mis-match.

In the days of hi-fi, we had to match power source (amplifier) and load (speaker) impedance, usually 8 ohm, to get the highest power transfer. To see this we don't use data, but we need the Volt/Amp/Ohm relationship for the system, and then use a differential equation.

In mechanical work transfer, we can think of two limit cases: lifting a feather, and lifting a ton weight. Lifting a feather over your head say 100 times a minute you'll get very tired, but do little work on the feather. Trying to lift a ton you'll get very tired, but will do no work at all. Most work is transferred somewhere in the middle.

[claus hansen]

Good answers. Measuring your heart rate can show you where your optimum is. For me it is 25 spm. for 10 kilomers/60 minutes. And a drag factor of 110. In cycling too, there is great individual variety, which is experienced and measured but can still not not be fully explained by neither physics nor physiology knowledge. Armstrong often used high kadences of 100-110 because it was effective for him, other riders (Ullrich, Riis) used very low kadences and higher gearing.

[gregsmith01748]

I reread the physics of ergometers and that suggests that higher strokes rates are more work on the erg because of the ratio of energy pushing yourself up and down the slide versus the energy going into the flywheel decreases. It says that it takes a 75kg rower 37 watts to slide back and forth at 30 SPM. At 20 SPM, this will only take 11 watts. So, say that you are rowing at 1:55 pace (230 watts). At 30 SPM, you are putting 267 watts into moving yourself plus spinning the flywheel. If you pull the same split at 20 SPM, you are putting 241 watts into the effort, or about 10% less.

This seems totally backwards to what I experience sitting on the machine. I can do an hour at 1:56 if I don't cap the rate, but if I limit myself to say 20SPM, I'm gassed trying to pull faster than 2:00. Is this really just a matter of personal physiology? Are there really people out there that can do an hour faster at 20SPM than 25SPM?

I am now officially puzzled.

[jlawson58]

I reread the physics of ergometers and that suggests that higher strokes rates are more work on the erg because of the ratio of energy pushing yourself up and down the slide versus the energy going into the flywheel decreases. It says that it takes a 75kg rower 37 watts to slide back and forth at 30 SPM. At 20 SPM, this will only take 11 watts. So, say that you are rowing at 1:55 pace (230 watts). At 30 SPM, you are putting 267 watts into moving yourself plus spinning the flywheel. If you pull the same split at 20 SPM, you are putting 241 watts into the effort, or about 10% less.

This seems totally backwards to what I experience sitting on the machine. I can do an hour at 1:56 if I don't cap the rate, but if I limit myself to say 20SPM, I'm gassed trying to pull faster than 2:00. Is this really just a matter of personal physiology? Are there really people out there that can do an hour faster at 20SPM than 25SPM?

I am now officially puzzled.

I bet this is similar to what I experienced with cycling. I was hooked up to a machine at a major university physiology lab and tested at 60, 80, and 100 cadences to see which was more efficient. For me, (not sure about everyone else) I was most efficient from a gas exchange (VO2max) standpoint at 60. However, in everyday trials with my power meter I found that I couldn't produce as much power over a given time period using that cadence as I could at a higher cadence. When I asked one of the leading exercise sports physiologists why, he told me that it was probably a result of the higher forces needed for each repetition at the lower cadence, fatiguing my muscles quicker than the more frequent, but lower, forces needed at the higher cadences. In other words, the savings from a VO2max standpoint were being overshadowed by the muscular fatigue I experienced by pushing harder but less often.

In the short time I have been erging I have noticed the same thing that you perceive. I wonder if this is true for everyone, or if it is more about the makeup of the percentage of slow vs fast twitch fibers that someone has. I would guess some of the fast twitch guys would do better with the stronger but slower pulls while the slow twitch guys prefer the faster ratings.

[gregsmith01748]

Well, until I read the stuff that I just posted about, I thought for sure that it was nearly universal that low ratings were tougher to maintain. In many things that I have read, people talk about "rating up" as they fatigue to try to maintain splits during a trial. If going faster is less efficient, then wouldn't it make you feel more tired?

I think that there might be something to the idea that the peak forces being higher in the low rating case, and this results in muscle fatigue. Is the relationship between muscle force applied and muscle energy consumed non-linear? I suspect it is some kind of a square law relationship or something.

[MRapp]

The wattage it takes to move up and down the slide is interesting, hadn't read that before. I'd imagine it all depends on your personal makeup and athleticism. The huge strong guy that doesn't have a great aerobic engine can probably perform better at low powerful rates. The thin guy with a huge aerobic engine will crank at high rates to accomplish a similar pace. The guy who can do both sets world records:) I happen to fall on the low rate side of the spectrum. My 30r20 pace is almost as good as my free rate 30 min PB, which I did at about 24-25.

[jamesg]

physics of ergometers; I quote:

..rough calculation.. Trying some numbers: for m=75 kg, s=1 m, R=30 str/min, this gives..

In that article, Dudhia takes 1 metre (presumably to simplify numbers) as the distance our CG moves during the stroke. This determines certain speeds, momentum and energy losses at inversion. In reality, the distance our CG moves on the erg is 50-60cm. So in fact the power losses are less than half the values he states, as kinetic energy is ½mv^2; and certainly negligible below rating 30.

The reason low rating is harder is that for the same power and stroke length, we have to pull harder. Pulling harder makes me tired all too soon, so I try not to do it. I suffer a wide variety of types of fatigue; the point is to limit those types that stop us too soon, so that we can train the others.

In any case the usual procedure for oarsmen is to find our best sustainable stroke with a certain amount of work in it (which identifies with net stroke length x average handle force) and then use that stroke at all ratings, so that Power is roughly linear with rating. Trying to paddle hard at low rating can be a part of learning to row, finding that stroke or of training for strength. Some use it for normal training (such as 30'/20r), but as any strength training it will overload and damage muscle, so may need a day extra recovery.

Rating up can be done by shortening for say 2 strokes, and then lengthening again to maintain the higher speed; it's called sprinting, and needs to be done with caution, possibly in the last 100-200 metres only.

[bobkwan2007]

Greg,
From the mathematical point of view it may not make sense, and all this math give me a headache anyway, but from a purely intuitive sense, it makes perfect sense. When you rate lower, the flywheel slows down a lot more, requiring you to generate much more force to accelerate it to some final speed. As you rate higher, the force required to accelerate it to the same final speed is less because the flywheel hasn't had as much time to slow down, and therefore making it seem easier to maintain the same speed.

I've done often in some of my workouts where I say I trade power for strokes when fatigue begins to set in.

[hjs]

I reread the physics of ergometers and that suggests that higher strokes rates are more work on the erg because of the ratio of energy pushing yourself up and down the slide versus the energy going into the flywheel decreases. It says that it takes a 75kg rower 37 watts to slide back and forth at 30 SPM. At 20 SPM, this will only take 11 watts. So, say that you are rowing at 1:55 pace (230 watts). At 30 SPM, you are putting 267 watts into moving yourself plus spinning the flywheel. If you pull the same split at 20 SPM, you are putting 241 watts into the effort, or about 10% less.

This seems totally backwards to what I experience sitting on the machine. I can do an hour at 1:56 if I don't cap the rate, but if I limit myself to say 20SPM, I'm gassed trying to pull faster than 2:00. Is this really just a matter of personal physiology? Are there really people out there that can do an hour faster at 20SPM than 25SPM?

I am now officially puzzled.

You are missing one thing. The lower rate, the more peakpower per stroke you need per stroke to get you upto pace. Rowing is infact giving power for a short while and breaking for a longer while, If you would do that in a car, giving gas and breaking, the shorter you give gas and the more you need to give, not just relatively but also absolutely.
The highest rate will always give te lowest peak power and the best result if we leave the energy expended on the slide away.

[NavigationHazard]

Sorry, you do NOT necessarily need higher peak power to maintain constant pace at lower rates, drag factor and drive duration and drive length equal. You need higher average power, one component of which may be higher peak power at some point during the drive. It depends on the force-curve profiles involved.

@bobkwan: it's true that the flywheel doesn't slow down as much at lower drag. OTOH in order to engage the sprocket and actually add handle force to the flywheel on the drive, you have to move the handle faster than you would at higher drag. Thus maximum efficiency at lower drag tends to demand the quick application of force at the catch. The faster the flywheel is spinning at the catch, the harder it is to catch up to it and accelerate it. And anything you're doing that's not accelerating the flywheel is wasted grunt.

[hjs]

Sorry, you do NOT necessarily need higher peak power to maintain constant pace at lower rates, drag factor and drive duration and drive length equal. You need higher average power, one component of which may be higher peak power at some point during the drive. It depends on the force-curve profiles involved.

Given a alike technique, lower rate means less strokes to get the same power output. So more power needed per stroke, more power per stroke makes the stroke is faster/shorter, so given this same technique a higher average power also simply means more peak power, no doubt whatsoever!
If not one is using a different technique, other factors kept constant.