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Hi netters,
Much has been said about the work done by a swimmer tethered at the
waist swimming _stationary_ in a pool. In this case I would like
to echo Paolo de Leva's comments regarding the principle of work.
> ... the concepts of work ... in ... application to the study of
> human motion is so complex that deserves either:
> a) a lot of study and a humble, doubtful attitude.
> or
> b) a lot of study, tons of effective thinking, and a good mind.
For practical reasons, I would suggest that it is safer to stick to
(a) :-)
As for the _study_ here are some useful references.
1. Knuttgen HG. Force, work, power and exercise. Medicine and
Science in Sports (and Exercise), 10(3):227-228, 1978.
Here the basic distinction is drawn that work has a particular
definition which is often confused with exercise or "effort".
Work = force x displacement.
Displacement is a vector quantity therefore in cyclic movements the
work should be zero. (Note the _should be_ :-)
The mechanical definition of the term work differs from the common
usage of the term work; for example to "work-out" in the gym.
If the weight-lifter returns the weights to the rack where he found
them, he (should have done) done zero work. He may have performed
many hours of exercise, but has (probably) done zero work. It is
perhaps unwise to insist too loudly/repeatedly that this is only a
"small semantic technicality", particularly within earshot of a
steriod-filled weight-lifter. (This is where the humble attitude
comes into it :-).
> Peter Davidson wrote:
> > ...Regarding your question on the amount of work done
> > during tethered swimming, I believe the answer is zero.
> Paulo de Leva wrote:
> I totally disgaree. It is true that the work done BY THE SWIMMER
> ON THE WEIGHT is zero, because the weight does not move. However,
> there's a lot of positive work done BY THE SWIMMER ON THE WATER.
> Peter wrote:
> > But the swimmer moves the water, so is not the swimmer doing work
> > against the water? To determine this work, you would need to know
> > the flow rate (volume (mass) and velocity)
This brings in the second point of confusion about work -- it is time
independant. Power is work x time. Again from the reference
material, it is better to refer to power when time is involved. By
introducing time (flowrate, velocity, instantaneous dislacements...)
we have digressed, and are no longer discussing work, but power.
The distinction needs to be borne in mind. Taken to its logical
conclusion imagine the swimmer swimming so slowly that the water is
hardly disturbed. The water that is pushed aside returns to fill
the gap. The _water_ has not displaced but individual molecules
have. You therefore you have to consider whether the swimmer is doing
work on the homogeneous _water_ or on the water molecules! The work
done on the _water_ is zero because it has not displaced (except for
that splashed out of the pool, of course ;-). However, this IS
measureable as a displacement of the weight.
The ultimate end point of any work is motion between perfectly
frictionless movements between molecules, which has another
name - - HEAT. Heat seems to come into it quite a bit (resulting in
heated debates, hot and sweaty exercises, people getting hot under
the collar, etc etc..) therefore let's look at the thermodynaic
definition of work as contained in the article:-
2. Webb P, Saris WHM, Schoffelen PFM, Van Ingen Schenua GJ,
Ten Hoor F. The mechanical work of walking: a calorimetric
study. Medicine and Science in Sports and Exercise, 20(4):331-
337, 1988.
Work = the energy transferred from a system NOT in the form of heat.
Now things get complicated because we cannot easily determine what
portion of the energy content of any given system ultimately
downgrades to heat (the term ultimately is safely used here because
we do know that work in independant of time). We also do
not know how much energy is stored in the system as body
fat, muscle glucogen etc. For this purpose, a thorough energy
balance here is essential; if one term is neglected or erroneously
estimated, then the whole calculation may be invalidated. (This is
where the tons of thinking and a good mind become necessary!)
I will pass on that one, but refer to another reference which
contains as complete an energy balance as I have seen anywhere.
3. Ward-Smith AJ. A mathematical theory of running, based on the
first law of thermodynamics, and its application to world-class
athletes. Journal of Biomechanics, 18(5):337-349, 1985.
The measurement of these quanties can be estimated or measured in a
whole-room calorimeter over a period of days (which allows the
energies to reach equilbrium).
The interesting conclusion of study [2] is that work IS done
during walking, but it is not done during cycling (please excuse any
misinterpretations here, as I am working (sic) from memory).
These results imply that not all the energy released from the human
body reappears as heat while walking; but all the energy reappears as
heat during cycling. Work can be seen as the mechanical transfer
of work across a boundary; it probably will dissipate as heat
within the receiving body, but may not :-).
At this stage, based on all this evidence -- and a great deal more
that I have not discussed -- I would hazard a guess that the work
done during swimming is also zero.
I base this assessment (in very, very, very, very broad terms on
the fact that cycling consists of cyclic motions as does swimming,
whereas walking is an oscillating movement :-). This conclusion is
based entirely on speculation -- and the wise reader should treat it
with the utmost sceptism... however I believe it to be correct.
If you want to test this assumption on a swimmer, you would have to
dress them in a thermal wetsuit and do the whole body calorimeter
experiment. The emersion of the body in water is so well suited
(sic) to a calorimetry experiment, that it would not surprise me if
it has not been done already.
Craig Nevin
Biomedical Engineer
Department of Physiology/Sports Science
University of Cape Town, South Africa
CNEVIN@anat.uct.ac.za
Much has been said about the work done by a swimmer tethered at the
waist swimming _stationary_ in a pool. In this case I would like
to echo Paolo de Leva's comments regarding the principle of work.
> ... the concepts of work ... in ... application to the study of
> human motion is so complex that deserves either:
> a) a lot of study and a humble, doubtful attitude.
> or
> b) a lot of study, tons of effective thinking, and a good mind.
For practical reasons, I would suggest that it is safer to stick to
(a) :-)
As for the _study_ here are some useful references.
1. Knuttgen HG. Force, work, power and exercise. Medicine and
Science in Sports (and Exercise), 10(3):227-228, 1978.
Here the basic distinction is drawn that work has a particular
definition which is often confused with exercise or "effort".
Work = force x displacement.
Displacement is a vector quantity therefore in cyclic movements the
work should be zero. (Note the _should be_ :-)
The mechanical definition of the term work differs from the common
usage of the term work; for example to "work-out" in the gym.
If the weight-lifter returns the weights to the rack where he found
them, he (should have done) done zero work. He may have performed
many hours of exercise, but has (probably) done zero work. It is
perhaps unwise to insist too loudly/repeatedly that this is only a
"small semantic technicality", particularly within earshot of a
steriod-filled weight-lifter. (This is where the humble attitude
comes into it :-).
> Peter Davidson wrote:
> > ...Regarding your question on the amount of work done
> > during tethered swimming, I believe the answer is zero.
> Paulo de Leva wrote:
> I totally disgaree. It is true that the work done BY THE SWIMMER
> ON THE WEIGHT is zero, because the weight does not move. However,
> there's a lot of positive work done BY THE SWIMMER ON THE WATER.
> Peter wrote:
> > But the swimmer moves the water, so is not the swimmer doing work
> > against the water? To determine this work, you would need to know
> > the flow rate (volume (mass) and velocity)
This brings in the second point of confusion about work -- it is time
independant. Power is work x time. Again from the reference
material, it is better to refer to power when time is involved. By
introducing time (flowrate, velocity, instantaneous dislacements...)
we have digressed, and are no longer discussing work, but power.
The distinction needs to be borne in mind. Taken to its logical
conclusion imagine the swimmer swimming so slowly that the water is
hardly disturbed. The water that is pushed aside returns to fill
the gap. The _water_ has not displaced but individual molecules
have. You therefore you have to consider whether the swimmer is doing
work on the homogeneous _water_ or on the water molecules! The work
done on the _water_ is zero because it has not displaced (except for
that splashed out of the pool, of course ;-). However, this IS
measureable as a displacement of the weight.
The ultimate end point of any work is motion between perfectly
frictionless movements between molecules, which has another
name - - HEAT. Heat seems to come into it quite a bit (resulting in
heated debates, hot and sweaty exercises, people getting hot under
the collar, etc etc..) therefore let's look at the thermodynaic
definition of work as contained in the article:-
2. Webb P, Saris WHM, Schoffelen PFM, Van Ingen Schenua GJ,
Ten Hoor F. The mechanical work of walking: a calorimetric
study. Medicine and Science in Sports and Exercise, 20(4):331-
337, 1988.
Work = the energy transferred from a system NOT in the form of heat.
Now things get complicated because we cannot easily determine what
portion of the energy content of any given system ultimately
downgrades to heat (the term ultimately is safely used here because
we do know that work in independant of time). We also do
not know how much energy is stored in the system as body
fat, muscle glucogen etc. For this purpose, a thorough energy
balance here is essential; if one term is neglected or erroneously
estimated, then the whole calculation may be invalidated. (This is
where the tons of thinking and a good mind become necessary!)
I will pass on that one, but refer to another reference which
contains as complete an energy balance as I have seen anywhere.
3. Ward-Smith AJ. A mathematical theory of running, based on the
first law of thermodynamics, and its application to world-class
athletes. Journal of Biomechanics, 18(5):337-349, 1985.
The measurement of these quanties can be estimated or measured in a
whole-room calorimeter over a period of days (which allows the
energies to reach equilbrium).
The interesting conclusion of study [2] is that work IS done
during walking, but it is not done during cycling (please excuse any
misinterpretations here, as I am working (sic) from memory).
These results imply that not all the energy released from the human
body reappears as heat while walking; but all the energy reappears as
heat during cycling. Work can be seen as the mechanical transfer
of work across a boundary; it probably will dissipate as heat
within the receiving body, but may not :-).
At this stage, based on all this evidence -- and a great deal more
that I have not discussed -- I would hazard a guess that the work
done during swimming is also zero.
I base this assessment (in very, very, very, very broad terms on
the fact that cycling consists of cyclic motions as does swimming,
whereas walking is an oscillating movement :-). This conclusion is
based entirely on speculation -- and the wise reader should treat it
with the utmost sceptism... however I believe it to be correct.
If you want to test this assumption on a swimmer, you would have to
dress them in a thermal wetsuit and do the whole body calorimeter
experiment. The emersion of the body in water is so well suited
(sic) to a calorimetry experiment, that it would not surprise me if
it has not been done already.
Craig Nevin
Biomedical Engineer
Department of Physiology/Sports Science
University of Cape Town, South Africa
CNEVIN@anat.uct.ac.za