Some may notice there has been mention of the Bernoulli Principle in

my postings in this thread. It has no relevance to the main

principles. There is a discussion of this in section of my web pages

entitled 'What are the biomechanics of swimming?' at URL

http://www.ozemail.com.au/~ohn/swim/2.html#1

John

: Point of clarification: Effective propulsive energy generated, over a

: given distance, can be simplistically equated to resistive force by

: overall distance travelled. Assuming resistance and rate of effective

: propulsive energy (or propulsive power) does not change in example

: below then the distance travelled per unit time, or pace, will not

: change.

: Resistance probably varies proportionally but crudely, over a narrow

: change of velocity range, according to k times v to the power of a,

: where k is a constant of proportionality that varies according to

: resistance profile, v is velocity and a lies between 2 and 3.

: John Heenan

: : Suppose a swimmer swims a 1500 meters aerobically in 1,000 seconds

: : using 10,000 arbitrary units of metabolic energy (as measurable

: : through oxygen consumption) using a late hip rotation against a

: : constant average resistance of 100 arbitrary force units with a

: : metabolic energy to effective mechanical propulsive energy efficiency

: : conversion factor of 10%. Ignore energy effects of dives and turns.

: : Suppose his optimal metabolic energy consumption is at this rate (that

: : is 10,000/1,000 = 10 metabolic energy units per second). Suppose

: : changes in style have no effect on his capacity to convert the

: : metabolic energy into effective propulsive energy at the same

: : efficiency. (It may even be more efficient for a swimmer to shorten

: : their stroke as stretching out stroke can result in utilising energy

: : less efficiently, early hip rotation or not). Suppose he takes 1000

: : complete stokes in the 1500 metres. That is one complete stroke per

: : second. Hence 10 metabolic energy units are being consumed in each

: : stroke cycle. Suppose, for simplicity, he stretches out his stroke

: : and times hip rotation earlier to obtain a more 'effective catch'

: : earlier. Suppose he expends 20 arbitrary units of energy per stoke

: : cycle. He is still consuming 10 metabolic units of energy per second.

: : Since energy conversion efficiency is the same and resistive force is

: : the same and he now completes the distance in the same time of 1000

: : seconds. But what is his stoke rate? He takes 20/10 = 2 seconds to

: : complete stoke. So nothing has changed in terms of time to complete

: : the distance. Although he generates more propulsuive energy per stoke

: : and slows stroke down, his overall swimming efficiency has remain

: : unchanged. However the liklihood of the following six factors

: : remaining the same is nil:

: : 1. Rate of metabolic energy consumed

: : 2. Metabolic to bodily mecahnical energy conversion efficiency

: : 3. Bodily meachanical energy to effective propulsive energy efficiency

: : 4. Metabolic to effective propulsive energy efficiency (involves both

: : of above)

: : 5. Resistive force

: : 6. Effective propulsive energy generated per stoke inversely

: : proportional to time to complete the stoke

: : While effective propulsive energy or metabolic to effective propulsive

: : efficiency energy may increase, it may be offset by an increase in

: : resistive force.

--

John Heenan Tel:(+612 or 02) 9580 3027 Fax:(+612 or 02) 9383 8064