As always I cannot resist these technical discussions. Please forgive me...
Richard Wizins wrote:
Maybe you are right Frederik, maybe not. I am personally not convinced that we can pedal very much more efficiently than most skilled cyclists already do.
This seems plausible. There is so much money in pro cycling that it would be unlikely that the pro teams haven't already done what's within the reach of scientific investigation to promote the highest possible efficiency.
This, of couse, dosen't exclude new scientific discoveries...
B. We have the issue of aerobic limitations. I.e. the cardiovascular system can not support an increase in power over any lenght of time even if we have the muscles to do it.
This I agree is the limiting factor for power output for most cycling activities.
energy. One could argue that it "only" prevents us from actually resting on the pedals on the upstroke and thereby counteracting the push on the other pedal. There is no telling how much power we actually add - it could well be nil.
Yes. The idea of Powercranks is to avoid spending some energy counteracting youself, i.e. pushing 'backwards' with one leg and 'forwards' with the other. Some energy would undeniably be saved if this can be avoided. It might be very little, though, maybe too little to bother. And maybe the action of actively lifting one leg instead of just letting it be lifted causes involvement of additional muscles, resulting in a nil gain or a loss. The human body is mechanically quite complicated (sic) and activating one muscle here generally requires another muscle there to be counteracting, to avoid the having body severely twisted...
Bikedrive on the other hand does address the problem of erratic power. If we accept that we have an spike of force on the down stroke (or up stroke by the way) which is in part lost on trying to overcome the bike's (and rider's) moment of inertia (weight basically, in this case) we have an interesting opportunity here. By storing part of the access force (energy actually) in the spring instead of "burning" it on a fruitless attempt to jump the bike forward we can use that energy during the otherwise virtually powerless 12-6 o'clock part of the cycle. Thereby we would add no new energy, but we would waste less of what we have on fruitless short accelerations (F=m*a).
Well, storing energy as spring tension or as momentum would make no difference, would it? Only the momentum storage is more light-weight, and has no termal losses...
BTW, the energy provided by each pedal stroke is small compared to the moving energy of the bike with rider, I think. I the energy of the moving bike was plotted, the pulsing caused by pedalling would be a tiny riddle on top of a comparatively steady line.
- My first impression of the Powercranks was a bit flawed. Their main
principle is preventing "resting" (pushing if you like) on the pedal in the up-stroke. Learning to use muscles to lift the foot will increase effective power (theoretically). If the power contribution in the up-stroke remains small (but not negative) it will do nothing to smooth the power curve. This might work, but I'm sceptical.
I am, too. But read the last lines below:
PUBLIC WARNING: THIS IS A LONG AND POSSIBLY CONFUSED MESSAGE.
The whole family is fine, thanks Jan-Inge! Give me a link to K-drive.
I'm glad that Frederik and I are not the only ones interested in turning this complicated issue inside out and back again :). Please everybody: don't get me wrong, I do see the potential of Powercranks as a training tool (to develop technique and other muscles) which will then help the cyclist to produce more anaerobic (se below) power on any type of cranks. I also agree that a good pedal cycle generally helps a lot, I'm not trying to discredit good pedalling technique. But I do doubt that it is possible to achieve much smoother power by better technique only. Apart from this I'm just trying to investigate (on request) the theory behind e.g. Bikedrive.
A few replies:
Göran: The power needed to overcome the dead spots at 12-6 is neglectable since the pedals are moving basically horisontally. Powercranks advantage (?) is in the phase (9-3) when you are (or should be) actually lifting one pedal. With or without Powercranks the 12-6 position is virtually powerless simply because of the fact that your body can't produce much forward/rearward force in those two leg positions. Producing enough power to overcome the dead spot without actually driving the bike is no great task ;). The same thing could, arguably, be said about the lift phase too. The fact that you lift the pedal doesn't neccessarily mean that you actually add any power to drive the bike. Consider pedalling without any load (e.g. drivewheel off the ground): the power you need to do this (not much, eh?) is the power you need to "lift" one leg with the other and to overcome the dead spots etc.. This is the power Powercranks are guaranteed to give you... You CAN of course gain more, but not automatically.
Concerning the cardiovascular capacity I think you are confusing aerobic and anaerobic power. My point is that you CAN increase short term power by using more muscles, as Frederik illustrates with the racing brothers, in this case we are talking about the anaerobic power (limited by lactate build-up). This is what you can use for up to a couple of minutes of sprinting. The aerobic power is when you are below your lactate threshold power and this is always limited by the cardiovascular capacity and economy (ability to use energy in an effective manner). This is the power you use for everything but the sprint efforts. Fit atheletes can stay close to their lactate threshold and produce high power for extended periods of time, but even they can't go above it for more than minutes.
Sverker: I actually thought you had me there for a while ;). But your idea about momentum to store the access energy is flawed. Remember that your cranks (and legs etc.) can't spin up instantly to store the access energy as momentum. To do that the whole bike would need to accelerate, which is my point exactly. The springs of the Bikedrive however allows energy to be stored during the pedal cycle without accelerating the whole vehicle. You also mix two completely different things when you talk about the power from the cyclist being a ripple on the energy curve. The only thing that drives the bike is the power from the rider. This power is all you have on the incoming power (energy) curve! The kinetic energy of the whole vehicle is simply the result of this power. All of the kinetic energy has come from the rider (if he wasn't starting down a hill). I think you were after the fact that the moment of inertia (tröghetsmomentet) of the vehicle is quite large compared to the forces we are talking about. This is what I have been trying to say all along: the power in the spike is in part lost trying to accelerate a relatively heavy object (the vehicle). A constant power would not have this "problem", all the constant power would be used to overcome rolling and wind resistance, thus at a higher speed. Bikedrives concept again :).
Boris: A flywheel would indeed work. The problem is that it must be very heavy or very large and it will still do the same thing as the springs do (in theory).
What I'm personally sceptical about whith Bikedrive is that this theroretically sound principle actually makes any difference in reality. It must to start with make up for the extra weight.
Still the gain is pretty simple to quantify: IF (!) we accept that some energy is "lost" by accelerating instead of maintaining constant speed then some of this energy is what is stored in the springs. Since you get all of that energy back during the pedal cycle less energy is lost. How much power this equates to is a simple function of rpm, spring rate and compression. I don't know either of the last two.
I know now that I must do one of two things: A: Calculate the theoretical gain, to see if it can possibly make a difference. B: Try it.
The optimal if this reasoning is right would be: - Train on Powercranks - Race on Bikedrive - As always: use the lightest possible bike (and body), to minimise energy lost on accelerations
All for now: over and out.
/Dick
PS I copied in Bikedrive, who knows - maybe they can clarify their fundamentals :)
----- Original Message ----- From: "Fridqvist, P.A.S." s.fridqvist@bwk.tue.nl To: hpvs@lists.lysator.liu.se Sent: Wednesday, October 23, 2002 9:39 AM Subject: RE: [hpvs] pedalling technique
As always I cannot resist these technical discussions. Please forgive
me...
Richard Wizins wrote:
Maybe you are right Frederik, maybe not. I am personally not convinced that we can pedal very much more efficiently than most skilled cyclists already do.
This seems plausible. There is so much money in pro cycling that it would
be
unlikely that the pro teams haven't already done what's within the reach
of
scientific investigation to promote the highest possible efficiency.
This, of couse, dosen't exclude new scientific discoveries...
B. We have the issue of aerobic limitations. I.e. the cardiovascular system can not support an increase in power over any lenght of time even if we have the muscles to do it.
This I agree is the limiting factor for power output for most cycling activities.
energy. One could argue that it "only" prevents us from actually resting on the pedals on the upstroke and thereby counteracting the push on the other pedal. There is no telling how much power we actually add - it could well be nil.
Yes. The idea of Powercranks is to avoid spending some energy
counteracting
youself, i.e. pushing 'backwards' with one leg and 'forwards' with the other. Some energy would undeniably be saved if this can be avoided. It might be very little, though, maybe too little to bother. And maybe the action of actively lifting one leg instead of just letting it be lifted causes involvement of additional muscles, resulting in a nil gain or a
loss.
The human body is mechanically quite complicated (sic) and activating one muscle here generally requires another muscle there to be counteracting,
to
avoid the having body severely twisted...
Bikedrive on the other hand does address the problem of erratic power. If we accept that we have an spike of force on the down stroke (or up stroke by the way) which is in part lost on trying to overcome the bike's (and rider's) moment of inertia (weight basically, in this case) we have an interesting opportunity here. By storing part of the access force (energy actually) in the spring instead of "burning" it on a fruitless attempt to jump the bike forward we can use that energy during the otherwise virtually powerless 12-6 o'clock part of the cycle. Thereby we would add no new energy, but we would waste less of what we have on fruitless short accelerations (F=m*a).
Well, storing energy as spring tension or as momentum would make no difference, would it? Only the momentum storage is more light-weight, and has no termal losses...
BTW, the energy provided by each pedal stroke is small compared to the moving energy of the bike with rider, I think. I the energy of the moving bike was plotted, the pulsing caused by pedalling would be a tiny riddle
on
top of a comparatively steady line.
- My first impression of the Powercranks was a bit flawed. Their main
principle is preventing "resting" (pushing if you like) on the pedal in the up-stroke. Learning to use muscles to lift the foot will increase effective power (theoretically). If the power contribution in the up-stroke remains small (but not negative) it will do nothing to smooth the power curve. This might work, but I'm sceptical.
I am, too. But read the last lines below:
From my own experience, I can tell the the max power gets higher if the pedals are both pulled and pushed. It is just a lot easier to climb a hill that way.
I can also say that that my feet tends to last longer if I try not to
press
on the pedals all the time. By lifting the feet att the return stroke, I
can
avoid the aching feet I will otherwise have after some time pedalling.
This,
btw, seems to be a recumbent problem. For mechanical reasons I assume the force pressing the foot to the pedal is actually higher on a recumbent
(with
a near horizontal leg) than on an upright (I will do some calculations
some
day).
My method to get a smooth round pedalling is to imagine my feet following the pedals, instead of pushing them. Try that, it gives a remarkable relaxed, flying feeling (on my Trice recumbent, at least)! The trouble is
to
keep this up for a prolonged time, some muscles seems to need training...
Sverker
HPVS mailing list HPVS@lists.lysator.liu.se http://lists.lysator.liu.se/mailman/listinfo/hpvs
On torsdag, okt 24, 2002, at 23:13 Europe/Amsterdam, Richard Vizins wrote:
Sverker: I actually thought you had me there for a while ;). But your idea about momentum to store the access energy is flawed. Remember that your cranks
Sorry, I used the wrong term, I should have written "inertia", not "momentum". My theory is sound, I think, see below.
The only thing that drives the bike is the power from the rider. This power the whole vehicle is simply the result of this power. All of the kinetic energy has come from the rider (if he wasn't starting down a hill). I think
I wouldn't deny that...
you were after the fact that the moment of inertia (tröghetsmomentet) of the vehicle is quite large compared to the forces we are talking about. This is
Yes, that's correct.
what I have been trying to say all along: the power in the spike is in part lost trying to accelerate a relatively heavy object (the vehicle). A
This is where I think you are lost. The energy, however, is not lost, it is stored as a minute increase of inertia (and thus speed) of bike + rider, and this extra inertia then drives the bike and rider over the dead spots. No need or use for additional springs in the system above those already there in the form of elastic materials of bike and rider's body.
The reason there is no perceived pulsation in speed is that the energy provided by the legs is small compared to the energy stored as inertia.
The benefits of a good circular pedalling technique, I say, is not smooth energy input per se, but better use of resouces, i.e. to spread the load on more muscle and to avoid having muscles work against oneother.
Sverker
-- Sverker Fridqvist, PhD Eindhoven University of Technology Faculty of Architecture * Design Systems Group http://www.ds.arch.tue.nl/General/Staff/sverker
Hmm, Confusion still rages. Maybe in part this is because we all struggle a bit to remember all the correct designations in english, so sorry Frederik I switch to swedish.
Sverker: Jag håller med dig till stor del. Jag slutade använda citationstecken om "lost" efter ett tag, men jag menade inte att energi försvann utan att den möjligen slösades bort. Hela kraften på pedalen måste naturligtvis mötas av en motkraft. I det här fallet de bromsande krafterna (luft- och rullmotstånd) och kraften som accelererar ekipaget. Knäckfrågan är egentligen: åtgår det samma energi att förflytta ett föremål med en viss medelhastighet med en konstant kraft som med en pulserande? Jag erkänner att jag inte vet, men mina hypoteser har byggt på att det "kostar" mer att omväxlande accelerera och låta deccelerera än att hålla konstant fart. Usch, ska jag verkligen behöva räkna på det här... Man kanske borde skicka frågan till någon mek-lektor. Eftersom luftmotståndet ökar kvadratiskt med hastigheten finns det naturligtvis en liten, liten vinst med att inte accelerera i onödan -men det var inte den vinsten jag tänkte på. Likaså blir det större friktionsförluster med höga krafttoppar - men det var inte det jag tänkte på heller. Jag skulle vilja se de rapporter som ledde till att Shimano utvecklade BioPace, de måste ha testat. Herr Müernseer på Bikedrive gav för övrigt följande påstådda nya empiriska bevis:
"This week, Dr. Juergen Eichhorn, one of the leading knee-spezialists in Germany made a testing of Bikedrive. He found out, that you need more than 20 % less pressure on the pedal to go on the same speed. This means less pressure on the knees which is very helpfull for people with knee-problems. And this means less energy needed of the muscles."
OM (!) detta skulle vara sant undrar man ju i sitt stilla sinne var den uteblivna energin sparas in någonstans om inte via effektivare utnyttjande på något sätt.
Göran: Ursäkta om jag missuppfattade dig. Jo jag håller med om att Powercranks är ett klyftigt sätt att träna nya muskler. Om det innebär att cyklisten kan producera vettig kraft i dragfasen kan det vara till stor hjälp. Framförallt för att utjämna kraften över pedalvarvet (jag tror fortfarande att det är viktigt, se ovan) och för att få bättre balans i benmusklerna. Sedan är jag tveksam om det verkligen leder till detta, den enda kraft Powercranks tvingar dig att tillföra är ju den som lyfter pedalen. Illustrationen med att cykla med bakhjulet i luften visar ju att den kraften inte är så stor. Du har naturligtvis rätt i att det ger ett litet bidrag, men jag är inte säker på att det har någon betydelse. Knäckfrågan i det här fallet är: kan man producera mer (och jämnare) effekt med fler muskler och större proportion dragkraft? Kanske, kanske inte... Roddcyklisten använder ju både rygg och armar, kan de producera mer effekt? Jag vet inte. Det känns spontant som om man skulle kunna vinna på att träna med Powercranks. Förmig är det dock uteslutet eftersom jag cyklar MTB. På en liggcykel skulle det bli läskigt eller?
Jag tror vi är överens om att vilka vinster man än kan få med dessa system så är de inte så väldigt stora. Norske mästaren i MTB hävdar i och för sig att han vinner två minuter per timme med Bikedrive, men det kan ju vara en psykologisk effekt. Skulle de 20% som Herr Müernseer påstår sig ha bevis för vara sanna vore det ju onekligen spännande. Systemet (muskler, hjärta/lungor, biomekanik, mekanik, motstånd, förluster) är så komplext att det är mycket svårt att uttala sig tvärsäkert, då återstår empiri.
Bikedrive låter en prova två veckor utan köptvång, så det ska jag nog göra. Jag kan testa hyfsat vetenskapligt med watt, kadens och pulsmätning. Jag återkommer med flipp eller flopp :). Någon frivillig för Powercranks?
/Dick
----- Original Message ----- From: "Sverker Fridqvist" s.fridqvist@bwk.tue.nl To: hpvs@lists.lysator.liu.se Sent: Friday, October 25, 2002 7:07 AM Subject: [hpvs] pedalling technique, continued...
On torsdag, okt 24, 2002, at 23:13 Europe/Amsterdam, Richard Vizins wrote:
Sverker: I actually thought you had me there for a while ;). But your idea about momentum to store the access energy is flawed. Remember that your cranks
Sorry, I used the wrong term, I should have written "inertia", not "momentum". My theory is sound, I think, see below.
The only thing that drives the bike is the power from the rider. This power the whole vehicle is simply the result of this power. All of the kinetic energy has come from the rider (if he wasn't starting down a hill). I think
I wouldn't deny that...
you were after the fact that the moment of inertia (tröghetsmomentet) of the vehicle is quite large compared to the forces we are talking about. This is
Yes, that's correct.
what I have been trying to say all along: the power in the spike is in part lost trying to accelerate a relatively heavy object (the vehicle). A
This is where I think you are lost. The energy, however, is not lost, it is stored as a minute increase of inertia (and thus speed) of bike + rider, and this extra inertia then drives the bike and rider over the dead spots. No need or use for additional springs in the system above those already there in the form of elastic materials of bike and rider's body.
The reason there is no perceived pulsation in speed is that the energy provided by the legs is small compared to the energy stored as inertia.
The benefits of a good circular pedalling technique, I say, is not smooth energy input per se, but better use of resouces, i.e. to spread the load on more muscle and to avoid having muscles work against oneother.
Sverker
-- Sverker Fridqvist, PhD Eindhoven University of Technology Faculty of Architecture * Design Systems Group http://www.ds.arch.tue.nl/General/Staff/sverker
_______________________________________________ HPVS mailing list HPVS@lists.lysator.liu.se http://lists.lysator.liu.se/mailman/listinfo/hpvs
Richard Vizins wrote:
Göran: Ursäkta om jag missuppfattade dig. Jo jag håller med om att Powercranks är ett klyftigt sätt att träna nya muskler. Om det innebär att cyklisten kan producera vettig kraft i dragfasen kan det vara till stor hjälp. Framförallt för att utjämna kraften över pedalvarvet (jag tror fortfarande att det är viktigt, se ovan) och för att få bättre balans i benmusklerna. Sedan är jag tveksam om det verkligen leder till detta, den enda kraft Powercranks tvingar dig att tillföra är ju den som lyfter pedalen.
_och_ som drar pedalen bakåt _och_ som pressar pedalen framåt. Jag tror dessutom att när man vant sig till att dra pedalen hela varvet runt, så kan man också lära sig att lägga en viss kraft hela varvet. Spekulationer, erkännes :-)
Illustrationen med
att cykla med bakhjulet i luften visar ju att den kraften inte är så stor. Du har naturligtvis rätt i att det ger ett litet bidrag, men jag är inte säker på att det har någon betydelse. Knäckfrågan i det här fallet är: kan man producera mer (och jämnare) effekt med fler muskler och större proportion dragkraft? Kanske, kanske inte...
Det är detta jag menar att jag entydigt upplever på mina träningsrundor när jag medvetet tänker på rundtrampet.
Roddcyklisten använder ju både
rygg och armar, kan de producera mer effekt? Jag vet inte. Det känns spontant som om man skulle kunna vinna på att träna med Powercranks. Förmig är det dock uteslutet eftersom jag cyklar MTB. På en liggcykel skulle det bli läskigt eller?
Bikedrive låter en prova två veckor utan köptvång, så det ska jag nog göra. Jag kan testa hyfsat vetenskapligt med watt, kadens och pulsmätning. Jag återkommer med flipp eller flopp :). Någon frivillig för Powercranks?
Tyvärr var priset sist jag kollade $700 :-( så jag avstår nog trots allt.
Mvh göran
/Dick
Richard Vizins wrote:
Göran: The power needed to overcome the dead spots at 12-6 is neglectable since the pedals are moving basically horisontally. Powercranks advantage (?) is in the phase (9-3) when you are (or should be) actually lifting one pedal. With or without Powercranks the 12-6 position is virtually powerless simply because of the fact that your body can't produce much forward/rearward force in those two leg positions. Producing enough power to overcome the dead spot without actually driving the bike is no great task ;). The same thing could, arguably, be said about the lift phase too. The fact that you lift the pedal doesn't neccessarily mean that you actually add any power to drive the bike. Consider pedalling without any load (e.g. drivewheel off the ground): the power you need to do this (not much, eh?) is the power you need to "lift" one leg with the other and to overcome the dead spots etc.. This is the power Powercranks are guaranteed to give you... You CAN of course gain more, but not automatically.
I agree in the above, but that is also a gain. It's better to have a small contribution from the not downpushing leg, than a negative contribution. The pulling up/back and pushing forward power is of course less but it is never the less significant. Don't you agree?
Concerning the cardiovascular capacity I think you are confusing aerobic and anaerobic power. My point is that you CAN increase short term power by using more muscles, as Frederik illustrates with the racing brothers, in this case we are talking about the anaerobic power (limited by lactate build-up). This is what you can use for up to a couple of minutes of sprinting. The aerobic power is when you are below your lactate threshold power and this is always limited by the cardiovascular capacity and economy (ability to use energy in an effective manner). This is the power you use for everything but the sprint efforts. Fit atheletes can stay close to their lactate threshold and produce high power for extended periods of time, but even they can't go above it for more than minutes.
Yes I'm very familiar with these concepts. But my point was that if I use more muscles to move the bike, I will go anaerobic at a higher power output. I can easily observe this every time I'm out on the road. If I engage the pulling up/back and pushing forward muscles, my HR goes up and the speed increases _without_ going anaerobic and _without_ reaching my limit for oxygen intake. The "new" muscles get tired after a while and the powercranks are supposed to help overcome that problem by forcing a training adaptation of those muscles. I haven't tried it (mostly due to the price of the cranks) but I think the idea is a sound one.
Mvh göran
hpvs@lists.lysator.liu.se skriver:
The whole family is fine, thanks Jan-Inge! Give me a link to K-drive.
Hello Mr Vizins I am glad everybody in the family is fine. Here's a link to a description of the K-drive. http://www.uct.ac.za/depts/psychology/bok/kdrive.html
Best wishes from
*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_:-.,_,.-:*
Jan-Inge Ljungberg webmaster@liggister.org www.liggister.org
-
Fridqvist, P.A.S. -
Göran Thyberg -
Jan-Inge Ljungberg -
Richard Vizins -
Sverker Fridqvist