Re: How much weight are you really carrying?

The message <61tck9F1urbn8U1@xxxxxxxxxxxxxxxxxx>
from Peter Clinch <p.j.clinch@xxxxxxxxxxxx> contains these words:

The link to kinetic energy was related to motion. Stand still and you
are still fighting gravity.

Only because I have to balance. In other words, balancing takes energy,
even though work = force x distance and I'm not moving any distance in
gross terms.

Balance is not what takes the bulk of the energy. Relax your muscles and
you will collapse in a heap.

Let us assume for a moment

<snip>
But how safe are all of these assumptions? We don't /really/ know, is
what I'm saying.

The assumptions are all of the right order of magnitude and could be
refined much further. We would need to quantify the kinetic energy loss
in the limbs to get a better idea of the energy needed to lift body mass
but I don't have enough information to do that reliably. In any event
the calculation was made to give a possible scenario. In a real
investigation the height rise would be established by modelling or
observation and the information used to compute the mechanical energy
required to overcome the losses.

As to the other figures used the 1.5 and 6.5 Kcals were derived by
experimentation and published in The Climber over 40 years ago and 20%,
apart from being a nice round number, is approximately middle of the
range of values that can be found on the Internet.

I have
already assumed that the arms don't take enough energy to worry about

As I've said a couple of times, I think the arm swings are a mere
by-product of something I'm not sure you can so easily rule out. Lots
of things are moving in cycles with plenty of friction and probably not
enough elasticity to rule things straight off the map.

ISTM that the friction you are thinking of is largely within the muscles
and thus cannot be distinguished other than as muscle inefficiency.

Since writing the above I have been googling to try and make sure the
efficiency I used was reasonable. I didn't find anything more but I did
come across the following:

"We sought to understand how leg muscle function determines the
metabolic cost of walking. We first indirectly assessed the metabolic
cost of swinging the legs and then examined the cost of generating
muscular force during the stance phase. Four men and four women walked
at 0.5, 1.0, 1.5, and 2.0 m/s carrying loads equal to 0, 10, 20, and 30%
body mass positioned symmetrically about the waist. The net metabolic
rate increased in nearly direct proportion to the external mechanical
power during moderate-speed (0.5-1.5 m/s) load carrying, suggesting that
the cost of swinging the legs is relatively small. The active muscle
volume required to generate force on the ground and the rate of
generating this force accounted for >85% of the increase in net
metabolic rate across moderate speeds and most loading conditions.
Although these factors explained less of the increase in metabolic rate
between 1.5 and 2.0 m/s (~50%), the cost of generating force per unit
volume of active muscle [i.e., the cost coefficient (k)] was similar
across all conditions [k = 0.11 ± 0.03 (SD) J/cm3]. These data indicate
that, regardless of the work muscles do, the metabolic cost of walking
can be largely explained by the cost of generating muscular force during
the stance phase."

2 metres per second is approximately 4.5 mph which is a fast walk in
most peoples book and just about flat out in mine.

I also came across an article that suggested that the "bobbing" of the
body during walking includes some pendular recovery which I had
previously discounted.

The more I read on the subject (unfortunately I can't access most of the
detail) the more I think that what I am suggesting has already been
calculated to the nth degree and it is only Nicks closed mind that has
prevented him from noticing the wealth of investigation that has
produced results.

--
Roger Chapman
Nearest Marilyn still to be visited - Great Orme.
89 miles as the crow flies,
considerably more as the walker drives.
.

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