View Full Version : Conversion of tethered swimming force to displacement

Lounsbury, David
05-06-2003, 06:25 AM
Greetings BIOMCH-L subscribers,

I am new to this group, but would like to pose what is, in my opinion, a
challenging research question.

For my M.Sc. project, I am studying the relative effectiveness of various
survival strategies for individuals who have been accidentally immersed in
cold (10 deg C) water. Subquestions relate to pacing strategies for
swimming, and the implications for swimming performance and thermal status
with or without a novel insulative device.

Unfortunately, practical restrictions have obliged me to adopt a tethered
swimming (TS) model. I will be able to rent an Olympic-sized pool to assess
baseline measures of swimming performance in my subjects, but I would not be
able to chill the water to 10 deg C. Also, my research facility lacks a
swimming flume. Therefore, I will need to use a 10 x 10 x 10 ft^3 cubic
tank that is equipped with a temperature controller. I plan to create a
harness that attaches to the subjects' waist, and to which a steel cable
(i.e. the tether) can be fixed.

I could only find a handful of studies that attempt to use a TS model for
training or measurement of swimming performance in the work physiology /
biomechanics literature. After browsing through Bonen et al (1980),
Rinehardt et al (1990), Kimura et al (1990), Lyttle et al (2000), and Yeater
et al (1981), I decided to base my system on the Yeater model, although I am
debating whether it is important to include the tension adjustable nylon
line that acts as a second tether between the subject and the pool side in

I then read a lot of studies by Dr. Huub Toussaint (a renowned swimming
biomechanist), who was kind enough to respond to an E-mail request for
information. He basically said three things: 1) 'natural' swimming
kinematics would likely be greatly affected by tethering, 2) it would be
difficult or impossible to differentiate between tether-manifested
propulsive force that would have been used to overcome active drag and
induce motion vs. that which would have been 'wasted' to accelerate masses
of water, and 3) the problem would be further complicated by the fact that
drag increases in proportion to (at least) the square of human swimming

As a third source of information, I browsed the topic 'tethered swimming'
within this newsgroup. There was apparently a rather heated debate on this
topic in 1995, but it mostly focussed on the calculation of work performed
during TS. My question (converting tether force to forward velocity, and
ultimately, swimming distance), is arguably even more difficult.

Besides the problems mentioned by Dr. Toussaint (above), the swimming
performance of the subjects in my study will also be directly affected by
the cold, in a manner that is difficult to quantify (Tipton et al, 1999;
Wallingford et al, 2000).

My current strategy (which is filled with holes) is as follows:

- test swimming performance during thermoneutral conditions in a pool where
subjects are free swimming (measure 'maximal' and 'endurance' velocities,
and make gross approximations of swimming efficiency by observation of
stroke rate and calculation of stroke length).
- test swimming performance during thermoneutral conditions in the tank
where subjects are performing tethered swimming (measure 'maximal' and
'endurance' tethered forces, which can be integrated over time and converted
to mean impulse). Stroke rate could still be measured to give one 'quick
and dirty' comparison to pool swimming. Here is the first big assumption:
swimming kinematics and propulsive force will be similar between
thermoneutral pool free swimming and thermoneutral tank tethered swimming.
Now for the second big assumption: knowledge of the mean impulse during
both maximal and self-selected endurance swimming can be directly compared
to measured maximal and self-selected endurance pace swimming performance
such that later, interpolations of these two impulse points can predict a
non-tethered swimming velocity.
- test swimming performance during cold (10 deg C) conditions in the tank
where subjects are performing tethered swimming (compare to thermoneutral
tethered swimming trial, given above). Based on differences between the
thermoneutral and cold tethered swimming regression equations (probably
subject specific) will be generated to predict swimming performance during
subsequent cold trials...a third big assumption.

- I am also hoping that certain anthropometric variables that will be
measured (e.g. body surface area, %BF, arm span, limb volumes) could help
predict interindividual differences in swimming velocity that would be
present for a given level of measured propulsive force. Unfortunately,
technical ability would probably be even more important for assessing
interindividual swimming velocity, but this is extremely hard to quantify.
- Also, we will be able to use indirect calorimetry (from expired gas
collections), to give more input into interindividual differences for
swimming efficiency, but practical issues dictate that we would only be able
to use intermittent measurements.

I know I have rambled on a fair bit, and my ignorance is probably apparent
on multiple levels. However, I am by no means a physicist (nor even a
biomechanist), and I am really hoping that I have been able to state my
problem clearly enough that some of you may be able to at least point me in
the right direction. ANY advice at all, however critical, would be much

Thanks for your time,

- Dave Lounsbury (University of Toronto/DND)

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