Performance and body weight

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Nomath
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Performance and body weight

Post by Nomath » November 27th, 2019, 11:36 am

Hi, I am new to this site. I use a Concept-2 rower at home for 6 years, about 200 sessions of 5000 meter a year. Whereas my best performance declined about 1% per year over first 4 years, it now seems to worsen much more rapidly, by about 5% this season. This made me worry about my general health.

Recently I had a sports checkup that includes a test on a bicycle ergometer. You are required to keep the pedaling pace constant at about 80-100 rpm while the resisistance increases linearly over time by 35W/min. At a certain time you can no longer keep the pace up and the peak power is recorded together with the heart rate. I had done a similar test in August-2018 and it turned out that I attained almost the peak wattage (330W) as 16 months ago!

This made me wonder what might be different between rowing and cycling. I registered a weight increase over the same period from 74.7 kg to 76.3 kg (averages of about 30 days), i.e. 2%. In cycling most of your body mass is kept static on the saddle, but in rowing most of the body is accelerating and decelerating forth and back. Supposing that muscle strength does not increase by gaining weight (mostly body fat, I presume), if more energy is spent in movement of the body, less will be available for transferring it to the rowing ergometer.

So I have questions:
1. Do others have a similar experience with declining rowing performance with increased body weight?
2. Could increase in weight explain the discrepancy between cycling and rowing?
3. Is there an estimate of the proportion of the energy output of the body that goes into body movement and into the ergometer?

jamesg
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Re: Performance and body weight

Post by jamesg » November 28th, 2019, 3:18 am

1. Only if the change in body mass is due to loss/gain of muscle and strength, or if the belly gets in the way of a long stroke. Most change is due to age or lack of specific training.

2. Not much. The main diff is that rowing is discontinuous. During the pull, our peak power output can be 3-4 times the average; during the recovery we can do nothing to the water or flywheel. Someone who can peak at 1hp during the pull (about 750W) will have an average power of around 250W at training ratings.To increase average power, we increase the rating, so that the idle time decreases; the stroke itself does not change much if we so decide.

This is why results in rowing are so heaviy dependent on training and style. We have to train both peak power AND the ability to deliver it repeatedy. This is done using more or less the same stroke as in a race, but with a longer recovery time between pulls.

I don't know if cyclists pull their pedals upwards too, but this could be a further difference.

3. Inertial power loss on the erg is the kinetic energy of our moving mass which is lost at both ends of the stroke, since muscle-tendon units cannot be considered elastic, i.e. they cannot absorb and release that kinetic energy, indeed they do work to slow us down into the catch. Our cg moves at around half the handle speed (so 1 m/s) and the moving mass can be guessed at about 80% of total, say 60 kg. KE increases with the square of speed, and there are more strokes at high rating. At training ratings, forget it.

To simplify and using 1 m/s both ways and 60 kg moving mass, KE is 60*1²/2 = 30 Nm. At rate 30, total loss per minute would be 30*2*30 = 1800 Nm, so power loss 1800/60 = 30 Watts.
78y, 188cm, 87kg, last seen MHR 159. 2k (2019-11-29) 8.33.8@23

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Carl Watts
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Re: Performance and body weight

Post by Carl Watts » November 28th, 2019, 9:06 pm

Basically the rower is nasty compared to a bike in that the bike is almost continuous and the rower has everything compressed into the drive and at low ratings your looking at huge power during the drive for it to then end up as a relatively low average power overall.

Typically more weight is more power for the same body composition but height gives you a big advantage also. You have to remember that there is a natural performance decrease with getting older.
Carl Watts.
Age:52 Weight: 104kg Height:183cm
Concept 2 Monitor Service Technician & indoor rower.
http://log.concept2.com/profile/863525/log

cleister
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Re: Performance and body weight

Post by cleister » November 29th, 2019, 9:48 am

How old are you?

Nomath
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Re: Performance and body weight

Post by Nomath » November 29th, 2019, 11:56 am

Thanks for the comments so far. I am new to the rowing community, although I used a C2 in the gym and at home for about 12 yrs now. Sorry, if I mis-use some rowing terminology.

I didn't mention my age: 71 yrs. Age is certainly a likely explanation for a steady decline in performance, but I still hope that it is not the full explanation for the big drop over the last 1-2 years.

Regarding cycling and rowing on an ergometer: cycling also involves a non-steady power output from the body, although not as extreme as in rowing. In a full pedal turn, the power input to the bike is max near 3 o'clock for the right leg and near 9 o'clock for the left leg. Power input is very low near 6 and 12 o'clock. At a cadence of 90 rpm, the power input has a typical frequency of 3 Hz. In rowing the power cycle is about 0.4 Hz.
Many investigations have shown that the upward pull on the pedals is negligible, even for professional cyclists. So each leg has a duty cycle of much less that 50%, similar to rowing.

The cycling ergometer test I was referring to used a ramp of 35W/min. This year I came to a stop at 336W at a heart rate of 160 bpm. So for about 4 minutes my power output was well above 200W. I associate 200W on a C2 with a 500m time around 2:00. The cycling test is probably more comparable to rowing 1000-1500 meter. Unfortunately my daily rowing runs are mostly 5K, which might involve a fatigue factor that was not present in the cycle test. My best 2K result this season is 8:27.9 ; last season it was 8:14.0 , an increase of about 3% in time. The power drop is considerably larger: from 186W to 171W average (8%)!

From the answers I understand that for the same test duration, the max power on a rower ergometer might be substantially less than on a cycling ergometer, because the body has long idling periods. However, this will also have been the case 16 months ago at my previous cycling test.

@jamesg : Thanks for the back-of-the-envelope calculation for the power loss from moving back-and-forth. 30W is not insubstantial, but accounting for a 2% increase in weight would not explain much. Additional losses from air drag on the body and rolling resistance are probably even smaller.

So for me there is a big unexplained discrepancy between my performance in cycling and in rowing.

jamesg
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Re: Performance and body weight

Post by jamesg » December 1st, 2019, 2:17 am

Mainly because the rowing forces have to go through trunk, shoulders and arms to hands, so all the muscle there has to be contracted, but does little mechanical work on the handle. You can see this by doing the backstop drill, setting the readout to Watts and watching the Watt/rating ratios.
78y, 188cm, 87kg, last seen MHR 159. 2k (2019-11-29) 8.33.8@23

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