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absolute beginner View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote absolute beginner Quote  Post ReplyReply Direct Link To This Post Posted: 16 February 2012 at 9:01pm
Interesting subject. I think of a body builder I know whose training regime involved bench pressing 150 kg for three sets of 10 repetitions. As he would put it with "good form" performing a deep full range movement. At this point he would fail to complete the final repetition. After a short break add 20kg and perform "half form" presses for three more sets to failure. He explained that he could lift more over the last four/ five inches of the exercise.
I asked if he thought the same would apply to a shorter crank set up on a bike. The foot position at bottom of the pedal stroke would be the same regardless of crank length. Due to the shorter uplift he reasoned that you should be able to produce as much (or more power), perform the motion more quickly, with less fatigue. One thing he did note was that reducing the overall crank stroke by 40mm (170mm down to 150mm) may be less noticable than reducing eighteen inches of arm travel in a bench press to the last four inches of the push.
 
Best wishes to all!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GeoffBird Quote  Post ReplyReply Direct Link To This Post Posted: 16 February 2012 at 10:05pm
Interesting 'cross-cultural' analysis Andrew. I've wondered whether the range of leg movement used in running would be most efficient for fast, repetitive work, as this is what human legs evolved for?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote absolute beginner Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2012 at 1:32am
Hi All. Sorry this turned into an essay.
 
Good point Geoff. You may have helped identify the answer to the short crank question. The action required by a bi-ped to make forward motion is to lose balance, regain it momentarily and repeat. What ever the discipline, walking, jogging or running, we are preventing ourselves from falling. If we are running we are aiming for an optimally efficient "stride length". This is something very personal and dependant on leg dimensions. For example Usain Bolt 6' 5" tall and me at 5' 9" are stood with our heels on the start line. We both walk out 10 strides and stand still. It would be fair to say I will be one or two of my strides behind Usain. I cannot increase my stride to compensate (legs not long enough)and decreasing my stride will reduce optimum efficiency. My only option is increase my leg speed. If Usain's leg speed is 1 then my leg speed needs to be 1.2 to keep up. As a runner. How do I do this? I increase my arm speed as the leg speed naturally tries to keep up. Success at beating Usain now depends on arm speed, leg speed and a miracle!
 
Only an opinion (a dangerous thing to have) the questions are far more than short crank? better? long crank? worse?
 
The brief would be for the required dimensions for a hpv, e.g. for me at 5' 9", which would give me optimum efficiency for the discipline I am undertaking? This should include investigation into an optimal crank length which will help me maintain X number of revolutions, with a given gearing, for the duration required without incuring injury. (Add aero requirements as needed).
 
The permutations equal a very large number. I would love to have the facility of time, money and technical expertise to test these variables.
  
I understand the HPV movement is already testing a variety of different crank lengths but there are still problems linked to standard size availability. I'm sure someone will create a formula which will help mathematically to find crank lengths which best suit an individual. 
 
Something to keep in mind. (I know these are powerstation cyclists)
In 1988 Francesco Moser ran a 1.03m diameter rear wheel to take hour indoor record.
In 1994 Miguel Indurain pushed 190mm cranks 100rpm on gearing 59x14. (Was this his optimum crank length for the discipline?) to take the hour record.
 
Mike Burrows may know what crank lengths Boardman and Obree used. I would be interested to know. Indurain was 6' tall I'm nor sure about the others. This may have an influence on the choice of crank size. He could have just needed extra leverage.
 
All the best.
   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill B-J Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2012 at 9:32am
Absolute beginner--
'Only an opinion (a dangerous thing to have)'--only if one attaches to it, and are not open to reality being different from the present perception!Smile

10 repetition maximum; an often used training protocol to get an increase in power largely. Maximum being subjectively set by the last repetition being difficult to complete with control. Many variations on how to use it. Like training a particular range of movement/ range of muscle length, and many other potential variables.

Running, multi factorial, complex. Being with the feeling of how it is, could be used as an assessment tool, and a way of allowing optimal neurological performance/ neuroplasticity---( neurological change,)--a view--> the  common 'scientific' reductionist view  overlooks the global picture---by definition. It is not only muscle and joints the move us.

My newly order Quest XS comes with standard 155mm cranks Big smile



Edited by Bill B-J - 18 February 2012 at 9:34am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hedgehog Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2012 at 1:42pm
Short cranks are available - I have managed to find a source of cranks of 155 mm in length, which are suitable for chain wheels with a pitch circle of 130 mm by 5 holes.
Also available are : Short crank 140 mm for 2 chainerings, pitch 110 mm.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GeoffBird Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2012 at 6:06pm
Hi Hedgehog, yes, 155s are fairly easy to get as I think they are used on kid's bikes. Sometimes they are reasonable quality. I bought some of these from Raptobike: http://www.raptobike.nl/components/drivetrain/cranksets/crankset-155mm.html  They are currenntly Euro 50.

As Andrew says, the physiological effects have to be offset against the aero effects. On an unfaired bike the 'pedalling envelope' is smaller with short cranks, but the foot-speed higher. Who knows which is better for aero, on arecumbent or an upright? In a faired bike the fairing can be made smaller with short cranks.

The Kingsbury K-Drive eliptical-path pedal system very effectively reduced fairing size in the 1980s, but (without wanting to put words in his mouth), I think even Miles Kingsbury would concede now that 120mm cranks may well achieve the same thing, with greater mechanical/pysiological efficiency. Delft Team take note! Smile

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Post Options Post Options   Thanks (0) Thanks(0)   Quote NickM Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2012 at 9:37am
Legs not being weightless, there is a significant oxygen cost associated with rotating them, even against zero load. This component of total oxygen cost is increased with the higher cadences typical of short crank use.

I would argue that leg strength is of little relevance to cycling performance, the overwhelmingly more important factor being blood supply to the working muscle.

The optimal crank length for an individual, nevertheless, may be influenced by the "recycling time" of muscle fibres. Short cranks may facilitate cadences which are optimal for people with predominantly fast-twitch fibres; people with predominantly slow-twitch fibres may be better served by longer cranks and slower cadences. Two people with identical limb lengths may not be equally efficient with cranks of the same length.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GeoffBird Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2012 at 9:56am
You've introduced another factor to consider Nick! Track sprinters have massive leg muscles, suggesting leg strength is important for this discipline, but not so significant for road racing, perhaps because muscle mass has to be carried up hills and presumably adds to drag?

This is all a bit more complicated than it first seems! A multi-disciplinary study of the issue would be required I think. Having worked with them, I'm sure UK Sport would be interested in this - they're very open-minded.

The fact remains, many people do find a benefit from shorter cranks than conventional wisdom dictates, and, even is there is zero biomechanical benefit, there is still the smaller fairing benefit, which anyone who has designed an HPV fairing will appreciate.


Edited by GeoffBird - 20 February 2012 at 9:56am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote tongskie01 Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2012 at 2:30pm
short cranks good for the knees. developing muscles for every descipline is key. track sprinters=power  road race cyling= both power and endurance. cavendish=excellent sprint finish but rubbish on hills. armstrong=good all rounder.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote NickM Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2012 at 8:20pm
Track sprinters have to get their only, rather high, gear going in a hurry from low speed or a standstill, so yes, they do need leg strength. But that is a very specialised scenario, so I think "little relevance" is pretty fair. I should really have said "endurance cycling performance", where "endurance" means any event lasting more than a few minutes.

Mark Cavendish is certainly an endurance athlete. You have to ride 300km before you reach the sprint finish in Milan-San Remo. I suspect that he also goes up hills rather faster than anybody who isn't a professional cyclist more orientated towards ascent. The time cut-offs for elimination in Tour stages are not all that generous.
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