Does going shorter cranks lead to increase in heart rate?
11-05-18, 02:36 PM
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Does going shorter cranks lead to increase in heart rate?
Had some nagging stuff in my knees and ankles so took about 3 weeks off and got a pro fit. The fitter had me go down from 175 to 172.5 in crank length. I've been back riding for a couple months. I'm close to 50 and am a large guy. I've noticed that my HR has jumped 10bpm on average across the board. I did a climb on Zwift today (the volcano) and usually around 80% exertion my HR used to top out at 165ish - today I hit 177 on a 6% grade doing about 190-215 watts / about 90 on cadence - am I'm thinking that can't be good - my FTP used to be 225 - the numbers I'm getting now are what I used to get when I'd really really push it. I have a Wahoo Tickr - maybe it's not giving me good data? Maybe it was the time off?
11-05-18, 02:40 PM
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It's not your crank length that is causing your HR to go up. I defy anyone to show that 2.5mm difference means anything anyway, but it's almost certainly loss in fitness from your 3 weeks off the bike. You are having to work harder to get the same power. Less fitness. It will get better if you keep at it.
11-05-18, 02:44 PM
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I think something else is causing your increase HR rather than a shorter crank. 2.5mm is nothing. Even with a 10mm change there’s no reason to assume your HR should increase that much. To keep the force on the pedals the same you’d need to increase cadence with the shorter cranks which would make your HR a little but 10 beats is a very large change so I suspect you just haven’t recovered the fitness you lost.
11-05-18, 03:29 PM
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It's the 3 weeks off, not the crank length that you need to worry about.
11-06-18, 05:33 AM
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Years ago when Sheldon Brown was alive I became an infrequent pen pal with him. We both had a science background and I always believed he had a transcendent knowledge of bicycles and so I would ask his opinion on different subjects and he was gracious enough to respond.
I asked him about crank length. He was just over 6' like me with pretty long legs. We were similar in size...except I have a more skinny cycling type body. He said he owned 60 bikes
His response about crank length was, he owned bikes with all different crank arm lengths. He owned just about every permutation of bicycle in fact. He said crank length doesn't matter for speed. Lennard Zinn, another great intellect on cycling, of course is famous or infamous for his position on crank length. He believes cranks should be proportionate to leg length. I am a bit in between on this. I have a 77.5 cm saddle height and ride 175mm cranks. Lance had shorter legs and lower saddle and rode 175mm as well. Lance rode closer to the Zinn formula and Zinn would likely put me on 180's or a bit longer.
That said, Sheldon Brown I believe is correct. I probably would be as fast or rather as slow
on anything from 165mm to 180mm. My hips would likely prefer shorter cranks as I age as I believe Mr. Brown's did and I would ride in likely a taller gear on 180's because of leverage, but my speed would likely be the same.
OP, I believe the answer is, for the same level watt output, no heartrate is not affected by crank length. The greater distance your feet travel on longer cranks for a single crank revolution is compensated by your choice of gear which affects pedal force and cadence. Work is the same. Gears on a bike are the great equalizer for crank length including your ability to adjust cadence.
I asked him about crank length. He was just over 6' like me with pretty long legs. We were similar in size...except I have a more skinny cycling type body. He said he owned 60 bikes
His response about crank length was, he owned bikes with all different crank arm lengths. He owned just about every permutation of bicycle in fact. He said crank length doesn't matter for speed. Lennard Zinn, another great intellect on cycling, of course is famous or infamous for his position on crank length. He believes cranks should be proportionate to leg length. I am a bit in between on this. I have a 77.5 cm saddle height and ride 175mm cranks. Lance had shorter legs and lower saddle and rode 175mm as well. Lance rode closer to the Zinn formula and Zinn would likely put me on 180's or a bit longer.That said, Sheldon Brown I believe is correct. I probably would be as fast or rather as slow
on anything from 165mm to 180mm. My hips would likely prefer shorter cranks as I age as I believe Mr. Brown's did and I would ride in likely a taller gear on 180's because of leverage, but my speed would likely be the same.OP, I believe the answer is, for the same level watt output, no heartrate is not affected by crank length. The greater distance your feet travel on longer cranks for a single crank revolution is compensated by your choice of gear which affects pedal force and cadence. Work is the same. Gears on a bike are the great equalizer for crank length including your ability to adjust cadence.
Last edited by Campag4life; 11-06-18 at 05:41 AM.
11-06-18, 07:36 AM
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I found going to slightly shorter crank arms made it easier to spin the big gears, which led me to want a bigger gear
11-06-18, 08:23 AM
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Shorter cranks are not more aero in and of themselves. They may allow you to take up a more aggressive aero position while opening up the hips and improving comfort and power. Shorter crank arms also require an increase in seat height, however, which may actually not be more aero for a few people.
11-10-18, 01:52 PM
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I have 170, 172.5 and 175. Virtually no difference between them. The 172.5 feel the best by a little, probably because that's what I've ridden the most.
11-10-18, 08:02 PM
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I did a climb on Zwift today (the volcano) and usually around 80% exertion my HR used to top out at 165ish - today I hit 177 on a 6% grade doing about 190-215 watts / about 90 on cadence - am I'm thinking that can't be good - my FTP used to be 225 - the numbers I'm getting now are what I used to get when I'd really really push it. I have a Wahoo Tickr - maybe it's not giving me good data? Maybe it was the time off?
11-10-18, 08:33 PM
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A mm is .03937" so no, less than 1/8" isn't gonna' set your HR sky rocketing.
Jon
Jon
