From: frank@molbio.cbs.umn.edu (Frank Williams)
Subject: Re: pedaling efficency
Organization: MBCC, Univ. of Minnesota
Date: Sat, 11 Apr 1992 09:22:02 GMT

This thread is interesting.  In my last post I alluded vaguely to "theoretical"
reasons why I thought it was better to recruit as much muscle as possible
for normal or non-climbing pedaling.  In this post I'll explain some of these
reasons and talk about some of the issues raised in Jobst's last post.

I apologize if the theory is taking us further from answering the question of
how best to pedal, rather than closer to the goal of optimizing our athletic
output.  Remember that, as "theory", I'm making this up as I go.  If YOU have
actual data, your duty as a card carrying cyclist is to post!  

The casual reader may wish to scroll down to the Section III and the summary.


I.   Optimizing muscle efficiency

Muscle works best when the intracellular pH is about 6.9 or above.
The harder a muscle works, the more acidic will be its intracellular fluid.
As the H+ ion concentration increases, calcium release for the purpose of
triggering contractions is inhibited.  We all know this from practical
experience.  Last Thurs. I saw the curve for this effect:  Ca++ release is
affected most as muscle first becomes acidic, and then approaches zero
asymptotically as more and more acid builds up.  In this way muscle protects
itself from serious damage due to overwork.  But anyway, a little acid -
whether lactate from anaerobic glycolysis or pyruvate, etc. from other
metabolic sources - will lower the strength of contraction.  I theorize that
the harder we work an individual leg muscle, the more acidic its intracellular
environment will be.  Whereas, as a greater muscle mass performs a fixed amount
of work, any drop in pH will be minimized by both the sheer tissue volume as
well as the greater capacity of the circulatory system to flush the acidic
"wastes" from the muscle cells.  

This brings up the circulatory system.  Nutrients get to muscle by simple
diffusion out of capillaries, followed by active or passive uptake into
muscle tissue.  Although the perfusion rate through very active muscle is
clearly greater than through relaxed muscle, the diffusion rate is fixed.
This argument is probably subject to considerable variation among individuals,
but I theorize that the kinetics of muscle fuel delivery are improved when
the delivery site is more evenly distributed among muscles, rather than
focused on fewer (more active) muscles.

Another variable that could confound clear conclusions in this debate is
muscle type - fast versus slow twitch.  An individual with a greater
proportion of fast twitch fibers would be more susceptible to the above
limitations because his or her muscle stores less O2, is less able to
aerobically metabolize its fuels, and is more dependent on circulatory
support.

The point is that, at some level of exertion, a smaller muscle will lose
out to a larger muscle.  Is that level of exertion reached during strenuous
aerobic cycling?  Speaking only for myself, I believe so.

II.  Jobst recently wrote the following about muscle overhead:

In article <9204092224.AA04081@hplomg.hpl.hp.com> BRANDT_JOBST/HP1900_01@HPLOMG.HPL.HP.COM writes:
>I believe that the human body is,
>in this respect, no different than all other "machines" in that each motor
>has its own overhead and that 100 one HP engines, for instance, burn more
>fuel than one 1 HP engine for the same output.  There are, no doubt, limits
>to this parallel but we are talking here of more then 90% of the work being
>done by the downstroke and whether including other muscles to augment this
>main muscle group improves energy conversion.  I believe it does not and
>I readily believe researchers who have not found any substantial work done
>by other muscles at peak output.

This is a logical argument. 
 
The problem I have is that I can't imagine any *additional* overhead that
results from recruiting an extra muscle.  First of all, the muscle is not
"off" when it is resting.  The efficiency of the metabolic pathways used in
basal metabolism is basically the same as when the muscle is producing work
(unless it's forced into an anaerobic state).  The work involved in lengthening
a flaccid muscle is not zero, but probably not significant.  In the kinds of
machines Jobst mentions in analogy, the sources of overhead are obvious.
Bearings, lubricant viscosity, noise, vibration, all straightforward.  How
about muscle?  The energy involved in maintaining vasodilatation is quite
negligable.  What else is there?  Heat.  But heat dissipation would be
enhanced by increasing active muscle volume and lowering the gain on each
individual muscle.  It is hard to equate mechanical with biological overhead.
From the standpoint of muscle and joint mechanics, it seems to wash.  From
the standpoint of metabolic energy generation, increases in biological 
overhead seem so small as to be negligable.

Bob Engel e-mailed me and reminded me of the considerable mass of the
hamstring muscle group, which flex the knee and allow one to "scrape"
past the bottom of the pedal stroke.  These are strong muscles - running
muscles.  I believe that they can easily be recruited not only for climbing
but to lower the biomechanical overhead in pedaling.  Specifically, one
can help smooth the pedal stroke and limit upper body compensation for
the moment that tends to rock the hips.  Does this involve more than 10%
of the power generation?  For me, no.  The question is how much other
overhead does it save?  In my own case, I believe the savings are significant,
particularly by the end of a long ride.


III.  Pulsed power and resting duration

Jobst's concept of rest duration may be a very useful one to examine.
How does pedaling style interfere with the cyclical rest that we generally
seek when the going gets tough?  If we recruit the hamstrings, we can rest
the quadraceps over the same range of pedal rotation?  Where does the rest
come from and why does pedaling round interfere?  Idea 1:  The hamstrings
can act like the adductor magnus and contribute to the extension of the hip.
This means that if we try to pull back past the bottom of the stroke and
pull back for too long, we will be resisting the subsequent upward movement
of the knee.  Idea 2:  Circulation in the legs is, I believe, influenced
by pedaling style.  Blood tends to descend through the core and return through
the periphery of the legs.  Do higher cadences help improve circulation?
I know that this is cycling "lore" but it seems that momentum shifts in the
calf could be beneficial.  Remember that the veins have 1-way check valves.
It is plausible.  Should round pedaling on the flats interfere with circulation?
In my opinion, only if it slows your cadence.  It is unclear to me what other
kinds of interference pedaling round could produce.  Quadracep resting time
should be the same, and quadracep power output is somewhat lessened.  

Summary:

The combination of the two ideas in Sect. III may help explain some of the con-
troversy surrounding pedaling style.  If one tries to keep the cadence high
and pull back hard at the bottom of the stroke, it is possible that the
long hamstrings will impede the flexion of the hip.  At slower cadences,
however, this wasteful tendency might be more easily avoided.  On the other
hand, the creeping fatigue that goes with "hammering round" may be partly 
due to more rigorous demands on the circulatory system in the legs - demands
that could be lessened by easing quadraceps use, keeping cadences up, and
not pulling back too far into the upstroke.  The benefits might then be due
to the reasons cited in Sect. I. 

Frank Williams
frank@molbio.cbs.umn.edu