elliptical engineering...

[Don Y]

On 2/25/2023 2:05 PM, Lasse Langwadt Christensen wrote:
> something like this: https://en.wikipedia.org/wiki/Eddy_current_brake#Dynamometer_eddy_current_absorbers

I have a little \"set of pedals\" that is used for physical
therapy (I guess... it was a rescue -- I was looking for a
foot powered generator framework).

It uses a DC motor as a generator feeding an \"electronic
load\".

[I thought it would be amusing to wire one up backwards
so when the patient started to pedal, the cranks would
\"suddenly\" turn at a high rate of speed of their own
accord!]

 

[RichD]

On February 26, ehsjr wrote:

The major component missing is wind resistance.
IIRC you only have to be doing about 15 MPH to require about 2/3 of your work
for overcoming wind resistance.

I have a little quiz, of science, math, economics, which I spring
on my friends and lawyer. The results are dismal, sad to say.

One: why is a bicyclist faster than a runner, whether sprint
or distance? Nobody yet has answered correctly - they
only spew word salads containing \'efficiency\' in multiple forms -

With a bike, all* of the leg motion is converted to
forward motion.

Not the rising leg.

With running there is up and down
motion as well as forward motion.

A good runner doesn\'t bounce, the center of mass remains
mostly level, that\'s a small loss.

> That\'s the essence of it.

Not close to explaining the colossal difference in efficiency
between running and biking.

--
Rich

 

[RichD]

On February 25, Lasse Langwadt Christensen wrote:

One: why is a bicyclist faster than a runner, whether sprint
or distance? Nobody yet has answered correctly - they
only spew word salads containing \'efficiency\' in multiple forms -

when running every time you land and have to lift you body again up
again some energy is lost

This is a relatively minor effect.

because of the weight of you legs there is a limit to how fast
you can swing them back and forth

Same for bicycling.
Anyway, swinging the legs faster, while running, would
merely burn more power, it wouldn\'t increase efficiency.

on a bike all the energy goes into moving you forward and you can pick
a gear that keeps the optimum speed of your legs for the speed you are
going, as long as you can produce enough power to do so

Again, that doesn\'t explain the efficiency/speed difference.

Look, in either case, the idea is to convert glucose into
forward motion, against losses. Does your metabolism
change, because you sit on a seat? Talk of gears and such
misses the point entirely.

You might try the popular wheel diameter explanation -
but I wouldn\'t advise it -

--
Rich

 

[RichD]

On February 25, Ralph Mowery wrote:

I have a little quiz, of science, math, economics, which I spring
on my friends and lawyer. The results are dismal, sad to say.
One: why is a bicyclist faster than a runner, whether sprint
or distance? Nobody yet has answered correctly - they
only spew word salads containing \'efficiency\' in multiple forms -

It would seem to me that the bicycle has the distance the feet move
multiplied by the ratio of the driving sprocket to the diameter of the
rear wheel. Similar to the way you trade power for distance in a set of
gears where one is larger than the other.

No, the gear ratio trades torque for distance, which is the
definition of mechanical advantage. It doesn\'t bear on
the question of energy usage.

For an engineer to trip over that, oh boy -

--
Rich

 

[ehsjr]

On 3/2/2023 5:01 PM, RichD wrote:
> On February 26, ehsjr wrote:

You have inserted quotes that were not in the post
to which I replied. I\'ll identify the insertions
with a line of equal signs.
============================================

The major component missing is wind resistance.
IIRC you only have to be doing about 15 MPH to require about 2/3 of your work
for overcoming wind resistance.

============================================

I have a little quiz, of science, math, economics, which I spring
on my friends and lawyer. The results are dismal, sad to say.

One: why is a bicyclist faster than a runner, whether sprint
or distance? Nobody yet has answered correctly - they
only spew word salads containing \'efficiency\' in multiple forms -

With a bike, all* of the leg motion is converted to
forward motion.

Not the rising leg.

You don\'t see the * where I wrote \"all*\"?

With running there is up and down
motion as well as forward motion.

A good runner doesn\'t bounce, the center of mass remains
mostly level, that\'s a small loss.

The runner is supporting his mass, against gravity,
100% of the time he is running. He is constantly
accelerating downward by gravity, and counteracting
that acceleration by accelerating upward with
muscle usage. That is NOT a small loss, whether or
not there is large perceptible bounce.

The biker\'s mass is supported, against gravity,
by the bike. Yes - since you mentioned it - he
does use some muscle power to raise the mass of
his legs but that is small in comparison to
supporting his entire mass.

That\'s the essence of it.

Not close to explaining the colossal difference in efficiency
between running and biking.

The OP seems to disdain efficiency in an explanation.
Quoting him again:

or distance? Nobody yet has answered correctly - they
only spew word salads containing \'efficiency\' in multiple forms -

Wind resistance can certainly reduce efficiency in a moving
bike, no question. To avoid those losses - and make efficiency
such a small factor that it can be ignored, consider bike
vs running speed at the gym - a treadmill vs a stationary
bike. You can go MUCH faster on the bike than on the treadmill,
and wind resistance is not a factor.

Aside from that, with a mass moving through air, wind resistance
goes as the _square_ of the velocity. So a bike going twice
the speed of a runner would have 4 times the wind resistance,
all other conditions being equal. I can\'t compare drag
coefficient and area between a rider hunched over on a bike
and the same person running - perhaps you can. Those affect
wind resistance and mean that all other conditions are not
necessarily equal.

Ed

PS - to the OP. I apologize for getting into all that, but
RichD raised good points, and deserves a reply with more
detail. Ed

--
Rich

 

[whit3rd]

On Thursday, March 2, 2023 at 2:01:58 PM UTC-8, RichD wrote:

On February 26, ehsjr wrote:

With a bike, all* of the leg motion is converted to
forward motion.
Not the rising leg.

If you use toe clips, the rising leg does pull up on its pedal.
That\'s only a small contribution, though; commuter cyclists rarely
bother.

With running there is up and down
motion as well as forward motion.
A good runner doesn\'t bounce, the center of mass remains
mostly level, that\'s a small loss.

I\'d claim that the inelastic foot-striking-ground was a major energy
loss for the usual gaits, and the cushioning in running shoes does get
quite a workout. Kangaroo locomotion uses special tissues for
spring-like efficiency.

 

[Carlos E. R.]

On 2023-02-24 22:47, RichD wrote:

I use the elliptical machine regularly, it\'s
the best full body workout, along with the rower.

I wonder, how do they implement the variable
resistance? hmmmm... a viscous damper? Place
a rubber diaphragm around the pushrods, fill
it with liquid, squeeze the bag with a stepping
motor, adjusting the viscosity.

There is a kind of brake, used to test motors, that is basically a
turbine rotating near another static turbine, both in a case filled with
water. The water can get hot and even boil, so it is renovated
constantly (when testing a motor).

--
Cheers,
Carlos E.R.

 

[Carlos E. R.]

On 2023-03-03 20:01, Carlos E. R. wrote:

On 2023-02-24 22:47, RichD wrote:
I use the elliptical machine regularly, it\'s
the best full body workout, along with the rower.

I wonder, how do they implement the variable
resistance?  hmmmm... a viscous damper?  Place
  a rubber diaphragm around the pushrods, fill
it with liquid, squeeze the bag with a stepping
motor, adjusting the viscosity.

There is a kind of brake, used to test motors, that is basically a
turbine rotating near another static turbine, both in a case filled with
water. The water can get hot and even boil, so it is renovated
constantly (when testing a motor).

Another kind, for slow motion, uses some magnetic dust with a rotor
inside. There is an electromagnet around it. When powered, the dust
solidifies in more or less degree, controlled with the current on the
magnets.

Not the kind for this usage, though, cooling would be difficult.

Magnetic and eddy currents is easy to do and regulate, water can be
flowed to cool it down. But the magnets are electromagnets for easy
regulation. Can be electronically controlled to emulate different type
of loading. Coupled to a motor, they can adjust for constant speed,
constant torque... whatever. Emulate going up a slope for a car,
overtaking, etc.

--
Cheers,
Carlos E.R.

 

[RichD]

On March 2, ehsjr wrote:
========================================

The major component missing is wind resistance.
IIRC you only have to be doing about 15 MPH to require about 2/3 of your work
for overcoming wind resistance.
========================================

Which applies to both runner and bicyclist.

I have a little quiz, of science, math, economics, which I spring
on my friends and lawyer. The results are dismal, sad to say.
One: why is a bicyclist faster than a runner, whether sprint
or distance

With running there is up and down
motion as well as forward motion.

A good runner doesn\'t bounce, the center of mass remains
mostly level, that\'s a small loss.

The runner is supporting his mass, against gravity,
100% of the time he is running. He is constantly
accelerating downward by gravity, and counteracting
that acceleration by accelerating upward with
muscle usage. That is NOT a small loss, whether or
not there is large perceptible bounce.

A human supports his mass all day long, and hardly
feels it. That isn\'t a factor here, in this question of
athletic performance.

The legs pump up and down, as the calf muscles cushion
the landings, that\'s a loss Still, in the larger picture, it\'s a minor factor.

The real energy expenditure, and loss, is in FORWARD motion,
not bouncing. Think about it: at higher speeds, the runner
fatigues, more than the biker, duh. Is there any difference in
the bounce?

The biker\'s mass is supported, against gravity,
by the bike. Yes - since you mentioned it - he
does use some muscle power to raise the mass of
his legs but that is small in comparison to
supporting his entire mass.
Wind resistance can certainly reduce efficiency in a moving
bike. resistance is not a factor.

Wind resistance doesn\'t \"reduce efficiency\", it\'s the primary drag,
to be overcome. Efficiency measures how well that\'s accomplished.

To avoid those losses - and make efficiency
such a small factor that it can be ignored, consider bike
vs running speed at the gym - a treadmill vs a stationary
bike. You can go MUCH faster on the bike than on the treadmill,
and wind resistance is not a factor.

You\'re confused. Efficiency isn\'t a factor to be ignored, it\'s central!

The point is, if a runner traveled at 25 mph, like a bike, he\'d face the
same wind resistance. But he CAN\'T run that fast, he can\'t overcome
those losses like the biker! Which is the whole point of the question:
why not?

By definition, the bike is more efficient. The runner is less efficient,
he suffers greater losses, in converting ATP into forward motion.
What/where are the losses?

No one in my experience has yet answered correctly. Of course it\'s
simple - after you see it -

--
Rich

 

[ehsjr]

On 3/3/2023 12:33 PM, whit3rd wrote:

On Thursday, March 2, 2023 at 2:01:58 PM UTC-8, RichD wrote:
On February 26, ehsjr wrote:

With a bike, all* of the leg motion is converted to
forward motion.
Not the rising leg.

If you use toe clips, the rising leg does pull up on its pedal.
That\'s only a small contribution, though; commuter cyclists rarely
bother.
With running there is up and down
motion as well as forward motion.
A good runner doesn\'t bounce, the center of mass remains
mostly level, that\'s a small loss.

I\'d claim that the inelastic foot-striking-ground was a major energy
loss for the usual gaits, and the cushioning in running shoes does get
quite a workout.

I used to get only about 300 -400 miles out of my running
shoes, and that includes the extra 50 (??) miles I got by
using hot glue to restore the \"nubs\" on the soles after each
run, once I was somewhere over about 200 total. I was doing
about 30 - 40 miles per week, so it got expensive.
Ed

Kangaroo locomotion uses special tissues for
> spring-like efficiency.

 

[ehsjr]

On 3/3/2023 4:14 PM, RichD wrote:

On March 2, ehsjr wrote:
========================================
The major component missing is wind resistance.
IIRC you only have to be doing about 15 MPH to require about 2/3 of your work
for overcoming wind resistance.
========================================

Which applies to both runner and bicyclist.

I have a little quiz, of science, math, economics, which I spring
on my friends and lawyer. The results are dismal, sad to say.
One: why is a bicyclist faster than a runner, whether sprint
or distance

With running there is up and down
motion as well as forward motion.

A good runner doesn\'t bounce, the center of mass remains
mostly level, that\'s a small loss.

The runner is supporting his mass, against gravity,
100% of the time he is running. He is constantly
accelerating downward by gravity, and counteracting
that acceleration by accelerating upward with
muscle usage. That is NOT a small loss, whether or
not there is large perceptible bounce.

A human supports his mass all day long, and hardly
feels it. That isn\'t a factor here, in this question of
athletic performance.

The legs pump up and down, as the calf muscles cushion
the landings, that\'s a loss Still, in the larger picture, it\'s a minor factor.

The real energy expenditure, and loss, is in FORWARD motion,
not bouncing. Think about it: at higher speeds, the runner
fatigues, more than the biker, duh. Is there any difference in
the bounce?

The biker\'s mass is supported, against gravity,
by the bike. Yes - since you mentioned it - he
does use some muscle power to raise the mass of
his legs but that is small in comparison to
supporting his entire mass.
Wind resistance can certainly reduce efficiency in a moving
bike. resistance is not a factor.

Once again, you misquote. I guess you\'re only here to
argue.

Wind resistance doesn\'t \"reduce efficiency\", it\'s the primary drag,
to be overcome. Efficiency measures how well that\'s accomplished.

If you wish to ignore losses, good luck in understanding efficiency.

To avoid those losses - and make efficiency
such a small factor that it can be ignored, consider bike
vs running speed at the gym - a treadmill vs a stationary
bike. You can go MUCH faster on the bike than on the treadmill,
and wind resistance is not a factor.

You\'re confused. Efficiency isn\'t a factor to be ignored, it\'s central!

So, using the example I posted - the gym comparison - please
show where efficiency _with regard to wind resistance_ is
central. I get the impression once again - I hope I\'m wrong -
that you only want to argue.

Ed

The point is, if a runner traveled at 25 mph, like a bike, he\'d face the
same wind resistance. But he CAN\'T run that fast, he can\'t overcome
those losses like the biker! Which is the whole point of the question:
why not?

By definition, the bike is more efficient. The runner is less efficient,
he suffers greater losses, in converting ATP into forward motion.
What/where are the losses?

No one in my experience has yet answered correctly. Of course it\'s
simple - after you see it -

 

[Don Y]

On 3/3/2023 4:36 PM, ehsjr wrote:

I\'d claim that the inelastic foot-striking-ground was a major energy
loss for the usual gaits, and the cushioning in running shoes does get
quite a workout.

I used to get only about 300 -400 miles out of my running
shoes, and that includes the extra 50 (??) miles I got by
using hot glue to restore the \"nubs\" on the soles after each
run, once I was somewhere over about 200 total.  I was doing
about 30 - 40 miles per week, so it got expensive.

I recall asking my MD (specialized in sports medicine) about the
\"costs\" of running (vs. walking); I figured if I *ran* (instead of
walked) I could meet my \"exercise quota\" in a third of the time!
And, it seemed only logical that the impact forces were greater
than during walking (standing BALANCED on two feet, each leg sees
a load of 50% of the body mass; walking, that rises to 100%
as the other leg floats; running, this increases to ~250-300%).

[Note that this ignores the \"unloaded\" time]

Running isn\'t claimed to be \"harder on your joints\" than
for non-runners (though it could also be that non-runners
likely includes a larger proportion of an overweight,
out-of-shape population!).

But, like you, I\'ve noticed I go through shoes at an alarming
rate (I walk ~19 miles/week). And, it\'s not just a wearing out
of the \"treads\" on the underside of the shoe; rather a complete
failure of the sole and the cushioning material therein.

[UNLIKE you, though, I don\'t bother to repair them. I just buy
three or four identical pair each time I shop for shoes so I
am not tempted to \"replace them tomorrow\" (and tomorrow becomes
next week/month/etc.). Instead, I toss them once I notice they are
looking pretty bad :-/ ]

Kangaroo locomotion uses special tissues for
spring-like efficiency.

The body stores (potential) energy in the tendons (and other \"elastic
structures\") to be converted to kinetic energy propelling the body.
But, the relative phases of these vary based on whether one is
walking (out of phase) or running (in-phase). Observations of how
the *body* (not just the legs) behaves in each gives insight into
how/where the energy is stored.

Of course, there are people who make careers out of studying this
sort of thing. <shrug> I can think of more interesting diversions
but, I guess, to each his own?

 

[RichD]

On March 3, ehsjr wrote:

One: why is a bicyclist faster than a runner, whether sprint
or distance?

The real energy expenditure, and loss, is in FORWARD motion,
not bouncing. Think about it: at higher speeds, the runner
fatigues, more than the biker, duh.

If you wish to ignore losses, good luck in understanding efficiency.

You\'re quite confused.

Last chance, Ed. Here\'s a big hint: race a runner vs. roller skater,
side by side. It isn\'t close. What explains the skater\'s advantage?
Or, the runner disadvantage?

Same answer for the bicyclist.

If you continue to flop around, without content, I have
to conclude you\'re just here to argue -

The point is, if a runner traveled at 25 mph, like a bike, he\'d face the
same wind resistance. But he CAN\'T run that fast, he can\'t overcome
those losses like the biker! Which is the whole point of the question:
why not?

--
Rich

 

[ehsjr]

On 3/5/2023 7:18 PM, RichD wrote:

On March 3, ehsjr wrote:
One: why is a bicyclist faster than a runner, whether sprint
or distance?

The real energy expenditure, and loss, is in FORWARD motion,
not bouncing. Think about it: at higher speeds, the runner
fatigues, more than the biker, duh.

If you wish to ignore losses, good luck in understanding efficiency.

You\'re quite confused.

Last chance, Ed. Here\'s a big hint: race a runner vs. roller skater,
side by side. It isn\'t close. What explains the skater\'s advantage?
Or, the runner disadvantage?

Are you dense? The skater is never airborne. The
runner is. I have to spoon feed you? Very well.
Each time the runner\'s foot lands - due to up and down
motion - that kinetic energy goes to zero. It has to be
replaced to keep the runner from falling flat on his
face, as the forward kinetic energy (while reduced) is
not totally lost.

The skater or cyclist or walker does not have the loss of
the same amount of kinetic energy, because he/she is never
airborne. His/her mass is supported by direct contact with
the ground 100% of the time. Most of the energy expended
goes to creating lateral motion. A runner spends energy
with every stride getting the body airborne - energy not
expended by the skater/walker/cyclist.

Compare sitting and standing. All other things being equal,
it is a whole bunch easier to sit than to stand. Why?
Because in standing your legs must support 100% of your
mass, which takes muscle and energy. In sitting, your
legs support a portion of you mass, but the greater
portion is supported by your butt. Think about it.
A cyclist is sitting. A runner isn\'t. You don\'t see a
difference?? When you understand the difference you
can visualize the force vectors involved and see where
energy must be spend. You can understand the obvious
losses that are inescapable. If you had accurate
measurements you could quantify how much of 1/2mv^2
energy was lost in each direction, how that reduced the
speed, how much energy had to be replaced and so forth.

But first, you have to recognize the difference in
motion between cycling and running, which you don\'t.
In fact, you first seemed to indicated that wind
resistance was the reason the cyclist went faster
than the runner. It had to be pointed out to you that
the cyclist faced greater wind resistance than the
runner.

Now, I\'m glad you mentioned \"Last chance, Ed.\"

Thanks.
Ed

Same answer for the bicyclist.

If you continue to flop around, without content, I have
to conclude you\'re just here to argue -


The point is, if a runner traveled at 25 mph, like a bike, he\'d face the
same wind resistance. But he CAN\'T run that fast, he can\'t overcome
those losses like the biker! Which is the whole point of the question:
why not?

--
Rich

 

[Lasse Langwadt Christensen]

torsdag den 2. marts 2023 kl. 23.21.40 UTC+1 skrev RichD:

On February 25, Lasse Langwadt Christensen wrote:
One: why is a bicyclist faster than a runner, whether sprint
or distance? Nobody yet has answered correctly - they
only spew word salads containing \'efficiency\' in multiple forms -

when running every time you land and have to lift you body again up
again some energy is lost
This is a relatively minor effect.

if it was minor running on a thread mill would be easy ...

because of the weight of you legs there is a limit to how fast
you can swing them back and forth
Same for bicycling.
Anyway, swinging the legs faster, while running, would
merely burn more power, it wouldn\'t increase efficiency.
on a bike all the energy goes into moving you forward and you can pick
a gear that keeps the optimum speed of your legs for the speed you are
going, as long as you can produce enough power to do so
Again, that doesn\'t explain the efficiency/speed difference.

it explains the speed difference, if you have the power to go faster but can\'t
move your legs any faster you need a gear

 

[Don Y]

On 3/6/2023 4:50 PM, ehsjr wrote:

Are you dense?  The skater is never airborne. The
runner is.  I have to spoon feed you?  Very well.
Each time the runner\'s foot lands - due to up and down
motion - that kinetic energy goes to zero. It has to be
replaced to keep the runner from falling flat on his
face, as the forward kinetic energy (while reduced) is
not totally lost.

The walker also expends energy in motions that aren\'t
*directly* producing forward motion -- e.g., spine twists,
arms swinging, etc. The rider (skater) also benefits from
inertia; a walker/runner can\'t really capitalize on his
inertia once his feet are planted -- the body has to absorb
(and dissipate) that energy.

If cycling was more efficient, then it wouldn\'t matter the grade,
eh? Yet, walking is more efficient (than cycling) for even
shallow inclines (e.g., 10%, IIRC, is the break-even point...
I see more incline on my ~FLAT street than that!). The cyclists
posture (and cadence) changes (uphill) making it less effective
to convert energy into motion.

You ride a cycle if you want to move long distances ON FLAT
(or, at least, not UPhill) TERRAIN. Some people like the
sensation of speed/distance covered. If you\'re planning on
any significant changes in elevation, then best to walk
(and leave the bike by the side of the road as that\'s extra
mass that you\'ll have to transport at an increase in energy
consumption).

If you\'re looking for exercise, then just put on your shoes and
go for a stroll -- but not at a \"leisurely pace\" (and, if you
REALLY want to burn calories, dig a hole and refill it -- many
times). If you can substitute a walk (or run) for a drive in
a car, then \"credit\" yourself with the time that would have
been spent \"riding\" to effectively increase the benefits of
the \"stroll\"

The skater or cyclist or walker does not have the loss of
the same amount of kinetic energy, because he/she is never
airborne. His/her mass is supported by direct contact with
the ground 100% of the time.  Most of the energy expended
goes to creating lateral motion.  A runner spends energy
with every stride getting the body airborne - energy not
expended by the skater/walker/cyclist.

And that is transferred into the sole of his feet when he
impacts the ground -- instead of being conserved in momentum.

Compare sitting and standing. All other things being equal,
it is a whole bunch easier to sit than to stand.  Why?
Because in standing your legs must support 100% of your
mass, which takes muscle and energy.  In sitting, your
legs support a portion of you mass, but the greater
portion is supported by your butt.  Think about it.
A cyclist is sitting. A runner isn\'t.  You don\'t see a
difference??  When you understand the difference you
can visualize the force vectors involved and see where
energy must be spend. You can understand the obvious
losses that are inescapable.  If you had accurate
measurements you could quantify how much of 1/2mv^2
energy was lost in each direction, how that reduced the
speed, how much energy had to be replaced and so forth.

But first, you have to recognize the difference in
motion between cycling and running, which you don\'t.
In fact, you first seemed to indicated that wind
resistance was the reason the cyclist went faster
than the runner. It had to be pointed out to you that
the cyclist faced greater wind resistance than the
runner.

Now, I\'m glad you mentioned \"Last chance, Ed.\"

Thanks.
Ed






Same answer for the bicyclist.

If you continue to flop around, without content, I have
to conclude you\'re just here to argue -


The point is, if a runner traveled at 25 mph, like a bike, he\'d face the
same wind resistance. But he CAN\'T run that fast, he can\'t overcome
those losses like the biker! Which is the whole point of the question:
why not?
--
Rich

 

[Don Y]

On 3/7/2023 12:12 AM, Don Y wrote:

If cycling was more efficient, then it wouldn\'t matter the grade,
eh?  Yet, walking is more efficient (than cycling) for even
shallow inclines (e.g., 10%, IIRC, is the break-even point...
I see more incline on my ~FLAT street than that!).  The cyclists
posture (and cadence) changes (uphill) making it less effective
to convert energy into motion.

<https://pedalchile.com/blog/cycling-vs-walking> claims the
break-even point to be \"2-3%\". That sounds ridiculously low!

\"During uphill cycling, speeds generally slow to such an extent
that aerodynamic drag is no longer a factor. The most significant
forces are gravity and the rider’s mass plus that of the bike.

Studies show that walking is more efficient than cycling once
a 2-3% gradient has been reached.

Cycling up a 10% gradients results in 800% more energy expended
than cycling on a smooth flat surface.

Mass of the rider, the bike, gravity and height gained all factor
in to how much energy is required to pedal up a specific hill. Once
a 2% grade is reached, even when pedaling in the lowest gear, it is
still more efficient to walk.\"

I will have to see if I can chase down his references (\"studies\")...

 

[RichD]

On March 6, Don Y wrote:

The skater is never airborne. The runner is.
Each time the runner\'s foot lands - due to up and down
motion - that kinetic energy goes to zero.

The walker also expends energy in motions that aren\'t
*directly* producing forward motion -- e.g., spine twists,
arms swinging, etc.
The rider (skater) also benefits from
inertia; a walker/runner can\'t really capitalize on his
inertia once his feet are planted -- the body has to absorb
(and dissipate) that energy.

Well, that\'s practically the whole story, finally.

Every time the runner\'s front foot plants, there\'s a huge
amount of kinetic energy lost. This dominates all other effects.
What happens when the skater\'s front foot lands? It\'s night
and day.

\"airborne\" is irrelevant, it\'s the lost FORWARD momentum
that\'s pertinent.

Interestingly, this effect is camouflaged, and reduced, by the
body\'s flexibility; i.e. the ankle and knee joints. Focus on his center
of mass, at his navel, and there\'s only a small loss of velocity.

If the body was stiff, the Tin Man, the effect would be obvious.
But as the body shifts shape, on each step, the center of mass also
shifts. Still, there\'s a big loss of energy on each step.

If cycling was more efficient, then it wouldn\'t matter the grade,
eh? Yet, walking is more efficient (than cycling) for even
shallow inclines (e.g., 10%, IIRC, is the break-even point...

Walking is a red herring. It\'s easy to believe that, at 4 mph, walking
is more efficient than cycling. That isn\'t the question. Obviously, at
low speed, there\'s less kinetic energy lost.

It\'s a comparison of athletic performance. A biker can easily do
20 mph. What happens when a runner attempts that?

--
Rich

 

[Don Y]

On 3/7/2023 5:02 AM, Don Y wrote:

On 3/7/2023 12:12 AM, Don Y wrote:
If cycling was more efficient, then it wouldn\'t matter the grade,
eh?  Yet, walking is more efficient (than cycling) for even
shallow inclines (e.g., 10%, IIRC, is the break-even point...
I see more incline on my ~FLAT street than that!).  The cyclists
posture (and cadence) changes (uphill) making it less effective
to convert energy into motion.

https://pedalchile.com/blog/cycling-vs-walking> claims the
break-even point to be \"2-3%\".  That sounds ridiculously low!

Hmmm... same blogger with different results:

<https://pedalchile.com/blog/uphill>

How to inspire confidence in your conclusions!