Biomechanics and Medicine in Swimming XI

was a definite peak associated with the left and right arms as they moved
through the cycle. The left arm peak occurred at 0.55s and the right at
1.07s. There was a secondary, lower peak that occurred prior to these, at
0.33s for the left, and 0.89s for the right arms.
The first phase was with the arm out in front of the head and appeared
to create an equal amount of drag for both arms of around -34N
to -38N; and lasted for between 0.09 and 0.11s. This is due to the drag
resulting from placing the arm into a zone of high moving water. The
hand was seen as the first point to start accelerating out of this extended
position when it begins to move at around 0.18s. This is followed by the
initial acceleration phase where the swimmer pushes out laterally from
the body and rapidly accelerates the hands and forearms; with a peak
force in this phase of between 50N and 100N. The force is governed initially
by accelerating the forearm and hand, and then slowly transitions
towards being more velocity based. The right hand had a 15% greater acceleration
and velocity in this phase, which partially explains the slightly
greater forces generated at this time.
The third phase appears to be a transition from the swimmer pushing
outwards by using mostly lateral muscles, and then begins to pull
inwards towards the midline of the body. The simulation showed considerable
deceleration by the forearm and hands at this point, and was
probably the reason for the decreased propulsion. Results indicated that
keeping this section of the pull-through at high acceleration and high
velocity would help improve the overall stroke technique.
The fourth phase was the main power pulling section of the stroke,
and achieved peak propulsive forces between 260N and 340N. It should
be noted that this peak force does not occur at either the peak acceleration
or velocity, of the hand or forearm. It also appears to occur just after
the swimmer exposes the best angle of the hand and forearm at 90º to
the direction of travel (see Figure 3). The swimmer’s peak instantaneous
velocity occurring just after this point substantiates that this force is a
true peak.
The fifth phase is the section where the arm exits the water and
is almost a point where drag is suddenly created. This could result from
the arm decelerating as it approaches the end of the stroke, or, also may
be due to some of the wave formation effects. The sixth phase is the
recovery where each arm, in turn, is out of the water.
Figure 3. Pressure graph depicting position of the peak net force during
the stroke.
conclusIon
The current study provided insight into how propulsion and drag forces
are generated throughout a full freestyle swimming stroke through the
use of CFD analysis. The resultant outcome of the analysis is both an
increased level of foundational knowledge related to the production of
propulsion and drag forces, as well as the provision of practical points
that may be used to improve freestyle performance.
reFerences
Bixler, B. & Riewald, S. (2001). Analysis of a swimmer’s hand and arm
in steady flow conditions using computational fluid dynamics. Journal
of Biomechanics, 35,713-717.
Bixler, B., Pearse, D. & Fairhurst, F. (2007). The accuracy of computational
fluid dynamics analysis of the passive drag of a male swimmer.
Sports Biomechanics, 6(1), 81-98.
chaPter2.Biomechanics
Loebbecke, A., Von Mittal, R., Mark, R. & Hahn, J. (2009). A computational
method for analysis of underwater dolphin kick hydrodynamics
in human swimming. Sports Biomechanics, 8(1),60-77.
Lyttle, A., & Keys, M. (2006) The application of computational fluid dynamics
for technique prescription in underwater kicking. Portuguese
Journal of Sport Sciences, 6(Suppl. 2), 233-35.
Sato, Y. & Hino, T. (2002). Estimation of Thrust of Swimmer’s Hand
Using CFD. Presented at 8th Symposium of Nonlinear and Free-Surface
Flows, Hiroshima, pp. 71-75.
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