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Re: Definitions of running (was RE: RE: Complaining)



Sorry, forgot I was stuck in rich-text mode. Wondered why no-one was
replying. Anyways - walking and running. An animal moving at steady
speed on swinging legs must place it's leg in front of it's centre of
mass for the first part of the stance period, and it's leg behind it
for the last part of the stance period. To stay upright and balanced,
this means that forces applied by the feet are pointing backwards
(i.e. braking) in the first part of stance, and pointing backwards
(i.e. accelerating) in the last part. To increase efficiency, it makes
sense to try and recover the energy lost in braking and re-use to
assist in accelerating. Walking and running are two separate classes
of energy recovery mechanism. In walking, you use the energy lost in
braking to raise your centre of mass upwards, turning your forwards
speed (ke) into potential energy (pe), vaulting over a relatively
stiff limb. In the last part of stance, you let you centre of mass
fall fowards on a relatively stiff limb, turning your pe back into
fowards speed, into ke. Hence ke and pe are out of phase with each
other in a walk - a 'pure' walk would have pe and ke fluctuating in
exactly opposite patterns, so 180 degrees out of phase (antiphase).

In a run, a different mechanism is used. Here, both the ke AND the pe
are used to compress biological springs (tendons) during the braking
phase, and it is the release of these springs that helps power the
accelerative phase. So in the braking phase, the body boths slows and
falls downwards, both of which compress the forwards/downwards facing
contact limb and stretch out it's springy tendons. In the accelerative
phase the limb recoils, speeding the body up and projecting it
forwards AND upwards. This is the 'bounce'. Hence ke and pe, working
together to compress the springs in the limb, are acting in phase with
each other. Again, a 'pure' run would have ke and pe exactly in phase
(0 degrees phase difference).

So, this phase-difference implies that there is a continuum between
walking and running, with two 'pure' endstates and a infinite variety
of intermediate states. This is true, theoretically you could use any
gait between a walk and a run, using different proportions of
gravitational vs elastic energy storage to transfer braking energy to
accelerating energy. However, at different speeds, given the size of
the animal, limb length, tendon properties etc, it will be
energetically more efficient to use one or the other. The maths can
get a bit involved, and I would be lying if I said I perfectly
understood gait transitions, but it is generally a case that animals
will switch from gravitational to elastic storage quite quickly over a
narrow range of speed differences. One thing that seems to be involved
is simply that at high speeds, at high ke, you would begin leaving the
ground if you use a walking gait anyway - the forwards energy is
greater than body weight, and so when you vault over a stiffened limb,
the energy exchange between ke and pe is enough to counteract gravity
through centripetal acceleration. Once you have left the ground, you
have a landing to collision to deal with, and it probably makes sense
to switch to a running gait and store that landing impact in springy
tendons.

But anyway, that is the biomechanically agreed-upon definition of
walking and running. Unlike footfall patterns it describes grounded
and aerial running accurately, as it is energy patterns and mechanical
limb use that is key, not whether or not you 'bounce' high enough to
leave the ground.

Vv

On 1 May 2013 10:01, Vivian Allen <mrvivianallen@googlemail.com> wrote:
> So, in more detail. An animal moving at steady speed on swinging legs must
> place it's leg in front of it's centre of mass for the first part of the
> stance period, and it's leg behind it for the last part of the stance
> period. To stay upright and balanced, this means that forces applied by the
> feet are pointing backwards (i.e. braking) in the first part of stance, and
> pointing backwards (i.e. accelerating) in the last part. To increase
> efficiency, it makes sense to try and recover the energy lost in braking and
> re-use to assist in accelerating. Walking and running are two separate
> classes of energy recovery mechanism. In walking, you use the energy lost in
> braking to raise your centre of mass upwards, turning your forwards speed
> (ke) into potential energy (pe), vaulting over a relatively stiff limb. In
> the last part of stance, you let you centre of mass fall fowards on a
> relatively stiff limb, turning your pe back into fowards speed, into ke.
> Hence ke and pe are out of phase with each other in a walk - a 'pure' walk
> would have pe and ke fluctuating in exactly opposite patterns, so 180
> degrees out of phase (antiphase).
>
> In a run, a different mechanism is used. Here, both the ke AND the pe are
> used to compress biological springs (tendons) during the braking phase, and
> it is the release of these springs that helps power the accelerative phase.
> So in the braking phase, the body boths slows and falls downwards, both of
> which compress the forwards/downwards facing contact limb and stretch out
> it's springy tendons. In the accelerative phase the limb recoils, speeding
> the body up and projecting it forwards AND upwards. This is the 'bounce'.
> Hence ke and pe, working together to compress the springs in the limb, are
> acting in phase with each other. Again, a 'pure' run would have ke and pe
> exactly in phase (0 degrees phase difference).
>
> So, this phase-difference implies that there is a continuum between walking
> and running, with two 'pure' endstates and a infinite variety of
> intermediate states. This is true, theoretically you could use any gait
> between a walk and a run, using different proportions of gravitational vs
> elastic energy storage to transfer braking energy to accelerating energy.
> However, at different speeds, given the size of the animal, limb length,
> tendon properties etc, it will be energetically more efficient to use one or
> the other. The maths can get a bit involved, and I would be lying if I said
> I perfectly understood gait transitions, but it is generally a case that
> animals will switch from gravitational to elastic storage quite quickly over
> a narrow range of speed differences. One thing that seems to be involved is
> simply that at high speeds, at high ke, you would begin leaving the ground
> if you use a walking gait anyway - the forwards energy is greater than body
> weight, and so when you vault over a stiffened limb, the energy exchange
> between ke and pe is enough to counteract gravity through centripetal
> acceleration. Once you have left the ground, you have a landing to collision
> to deal with, and it probably makes sense to switch to a running gait and
> store that landing impact in springy tendons.
>
> But anyway, that is the biomechanically agreed-upon definition of walking
> and running. Unlike footfall patterns it describes grounded and aerial
> running accurately, as it is energy patterns and mechanical limb use that is
> key, not whether or not you 'bounce' high enough to leave the ground.
>
> Vv
>
>
> On 1 May 2013 08:46, Vivian Allen <mrvivianallen@googlemail.com> wrote:
>>
>> Dudes, seriously. Its the degree to which there is congruence between ke
>> and pe. This was settled a while ago.
>>
>> Vv
>>
>> On May 1, 2013 6:24 AM, "Jaime Headden" <qi_leong@hotmail.com> wrote:
>>>
>>> Ah, so now you need a "bounce" (elephants have this), and a "suspension
>>> phase" (elephants lack this, but gallopers have this). Gosh, your argument
>>> is JUST AS ARBITRARY as theirs. However, unlike yours, their use of the
>>> definition is founded on kinematic and biomechanical forces entirely. Yours
>>> required a slam on Muybridge (deserved or otherwise) to make -- in your
>>> ineffable manner.
>>>
>>> It's becoming clear that whatever the needs, here, what the bounce
>>> describes (which alters how mass is moved even in a stable movement pattern
>>> such as a walk) and what the suspension phase describes are two entirely
>>> different things. In a biomechanical sense, these are two separate things,
>>> but you are trying to conflate them. You fail to consider a neat, useful and
>>> generally elegant pattern because it allows an animal you don't like to
>>> think about as "running" to be classified as a runner. What you seem to want
>>> is that an animal has to "gallop" to "run," and this is an unshakable
>>> premise. Nothing runs unless it "gallops."
>>>
>>> Cheers,
>>>
>>>   Jaime A. Headden
>>>   The Bite Stuff (site v2)
>>>   http://qilong.wordpress.com/
>>>
>>> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>>>
>>>
>>> "Ever since man first left his cave and met a stranger with a
>>> different language and a new way of looking at things, the human race
>>> has had a dream: to kill him, so we don't have to learn his language or
>>> his new way of looking at things." --- Zapp Brannigan (Beast With a
>>> Billion Backs)
>>>
>>>
>>> ----------------------------------------
>>> > Date: Tue, 30 Apr 2013 21:46:08 -0400
>>> > From: GSP1954@aol.com
>>> > To: dinosaur@usc.edu
>>> > Subject: Re: Definitions of running (was RE: RE: Complaining)
>>> >
>>> > "We do find evidence that elephants run in a sense,"
>>> >
>>> > said first author John Hutchinson, a Stanford
>>> >
>>> > postdoctoral research fellow in the Department of
>>> >
>>> > Mechanical Engineering. "It's an intermediate
>>> >
>>> > sort of gait, but it looks like what we
>>> >
>>> > biomechanically would call running. They don't leave
>>> >
>>> > the ground, which is the classical definition, but
>>> >
>>> > they do seem to bounce
>>> >
>>> > definition."
>>> >
>>> > The problem with saying that elephants can run is that elephants cannot
>>> > really run the way most mammals can. Saying animals can either just
>>> > walk or can
>>> > run is to simplistic, there are as above notes transitional forms like
>>> > elephants that have barely some running attributes, but are much slower
>>> > than
>>> > most mammals and cannot even trot like hippos much less gallop like
>>> > rhinos (not
>>> > a simple size thing, an adult horse the same mass as a juvenile
>>> > elephant is
>>> > almost three times faster, its the flexed limbs and perhaps mass
>>> > dedicated
>>> > to locomotion that makes the difference).
>>> >
>>> > The way it should work is this.
>>> >
>>> > If an animal cannot achieve "a bounce" nor a suspended phase then it
>>> > cannot
>>> > run and is only walking (fits salamanders I think, turtles, maybe the
>>> > biggest sauropods since even just walking their long strides could have
>>> > gotten
>>> > them to the elephant max of 15 mph).
>>> >
>>> > If it can achieve a bounce in a least one set of limbs but cannot
>>> > bounce
>>> > enough to get all feet off the ground at the same time then it is
>>> > semirunning
>>> > or ambling (elephants, unitatheres, most sauropods, derived
>>> > stegosaurs).
>>> >
>>> > If it can achieve enough bounce to get all feet off the ground then it
>>> > is
>>> > achieving a full or true run (bipedal run, hopping, trot, pace, canter,
>>> > gallop) (most limbed reptiles, most all dinosaurs including giant
>>> > theropods,
>>> > giant ornithopods, giant ceratopsid, big ankylosaurs [albeit barely],
>>> > many
>>> > birds, most mammals including hippos [they can really haul all that fat
>>> > around on
>>> > those dinky limbs, no point in trying to outrun one], brontotheres,
>>> > indricotheres).
>>> >
>>> > GSPaul
>>> >
>>> > </HTML>
>
>