Sheldon Brown <[email hidden]> wrote in message news:<[email hidden]>...
Quoted message said:Carl Fogel queried:
Quoted message said:On a related note, why do distance swimmers use both their arms and legs? Why do cross-country
skiers use their poles while striding? I'm ignorant of these sports, but have the impression
that they involve using all four limbs, not just two, and make huge cardiovascular demands.
I can answer that.
A bicycle has a very efficient drive train, solidly coupling the legs to the propulsion system.
There are small frictional losses, but virtually no slippage to the drive train.
A swimmer or skier has a very much less efficient way of converting leg effort into propulsion due
to the natures of the respective media.
A skier does have good coupling for the arm component of propulsion, but arms are way weaker
than legs.
Sheldon "Impedance Matching" Brown
Dear Sheldon,
Where I'm not following you is why it matters how well the limbs are coupled. I think that I see
what you're saying. Chains work well, splashing is inefficient, and weak arms with good purchase
through a ski pole become useful when the alternative is slipping on the snow. (I expect the
swimmers and skiiers are gnashing their teeth.)
Where I'm not following you is why it matters how well the limbs are coupled on the bicycle. That
is, my arms and legs don't care what the result is, as far as I can see. They just wave hopefully
at whatever my cardiovascular limit may be and are turned into forward motion by equally
effective chains.
The question seems to be how do various combinations of limbs affect the ratio between effort and
cardiovascular limits.
Arms might work more efficiently than legs, but this seems unlikely. (Why? Because that's my
prejudice. They're smaller, and smaller muscles are less efficient. That's why weightlifters with
bulging leg muscles beat skinny fellow at marathons . . . Fine, I don't have an explanation, but
that's how I feel.)
Or arms might work roughly as well as legs, but then they wouldn't be practical because of the
burden of the extra transmission.
Or it could be that whatever the relative efficiency of the arms and legs at using the heart and
lungs turns out to be, it nevertheless helps to spread the effort out over four limbs (or quite the
opposite). I think that Jobst has argued for using fewer muscles.
Or the arms might use the cardiovascular system less efficiently than the legs for some reason and
therefore waste the available effort internally, not externally as with ski-poles versus ski-
bottoms, or kicking versus arm-strokes in the pool.
(I was fascinated to read in an earlier rec.bicycles.tech thread that swimmers get their propulsion
from arm-strokes, not leg-strokes:
groups.google.comgroupsOpen ↗
Of course, Tom Kunich may be insane, but I hope not. I always thought that legs were what mattered
in swimming and like to be startled.)
Or . . .
I have an uneasy feeling that the topic is not nearly as cut and dried as some posts declare.
In general, I incline to the idea that a pair of legs is by God all that we need and using any other
muscles is durned foolishness!
(Besides, how the hell do you set up an arm-crank that can be used comfortably for long distances?
And how do you train yourself to spread the effort out over four limbs instead of two? Two legs work
pretty durned well, you damned sodbusters! And--and--well, none of this really addresses
cardiovascular resources and whether two limbs or four use them better.)
I can't quite follow Jobst's "one leg will pedal as well as two" theory. His proposed experiment
seems to be well below cardiovascular limits, must be performed on level ground, and doesn't explain
how he can tell the effort is the same with one leg as with two or with one power stroke every third
time. I've asked him again, so he may explain these things--or may have explained them elsewhere
years ago.
I haven't got a good answer for Phil Holman's recent comment in this thread about how odd it is that
our cardiovascular limits should just happen to match our leg muscles:
Quoted message said:And it just so happens that the limiting factor for cycling occurs at the point when the quads and
glutes are fully developed and engaged and not one muscle fibre more (tongue in cheek) What a
coincidence.....don't you think?
I'm not asking for much. Just give me a brief, clear, all-encompassing explanation of the mechanics
of several complicated sports and most of human physiology, plus a lot of tricky details about
physics and practical applications. Let me know as soon as it's all worked out and you all agree!
Seriously, I do appreciate your suggestion about skiing and swimming. You certainly addressed
my question, so I'm pleased, but I probably need to figure out how to ask my real question a
lot better.
Thanks,
Carl Fogel
