Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
Comparison of Front Crawl Swimming Drag between
Elite and Non-Elite Swimmers Using Pressure
Measurement and Motion Analysis
Ichikawa, h. 1 , Miwa, t. 1 , takeda, t. 2 , takagi, h. 2 , tsubakimoto,
s. 2
1 Japan Institute of Sports Sciences, Tokyo, Japan
2 University of Tsukuba, Ibaraki, Japan
The purpose of the study was to suggest a methodology to quantify the
drag force during front crawl swimming and to compare the drag force
between elite and non-elite swimmers. Subjects were asked to swim
front crawl using arms only in swimming flume, which set the velocity
to 1.3 m/s. The pressure distribution on the swimmer’s hands and
the orientation of the swimmer’s hands were measured to calculate the
propulsive force. The position of the umbilicus was recorded using high
speed camera with 250 fps to calculate the swimming acceleration. The
drag force was estimated according to the equation of motion “ma = Fp +
Fd” along with swimming direction. The elite swimmer swam efficiently
with lower drag force (averaging at 21N) compared to the non-elite
swimmer (average 50N). Our methodology would be useful to compare
the dynamics and to discuss the performance of swimming.
Key words: drag force, propulsive force, inertial term, dynamics, front
crawl swimming
IntroductIon
The dynamics of swimming is expressed as a mass model,
ma + F
100
= Fgra
+ Fsta
dyn
(1)
where m and a are a swimmer’s mass and acceleration vector of the
swimmer’s whole body. F gra is downward force vector due to gravity, F sta
is upward hydrostatic force vector that is called buoyancy, and F dyn is
unsteady hydrodynamic force that Namashima (2006) was modelling as
tangential and normal resistive fluid force, which are proportional to the
local flow velocity, and inertial force due to added mass, which is proportional
to the local flow acceleration. The component on the swimming
direction of Equation 1 was expressed as,
ma +
= Fdyn−
swim = Fp
Fd
(2)
where a and F dyn-swim are the component along with swimming direction
of a and F dyn , respectively. The F dyn-swim is separated into forward force
F p , which is propulsive force, and backward force F d , which is drag force.
Many researchers have suggested some methodologies to quantify the
drag force in swimming as “active drag”, although it is difficult to quantify
the drag force in swimming (Di Prampero et al. 1974, Clarys et al.
1974, Hollander et al. 1986, Kolmogorov et al.1992). The methodologies
have some assumptions, such as “swimming velocity is constant” (Di
Prampero et al. 1974, Hollander et al. 1986), “propulsive and drag force
are in balance” (Clarys et al. 1974, Kolmogorov et al. 1992). Almost all
previous researches expressed the drag force as a single value, which was
a mean value during some strokes. The drag force is, however, changing
from moment to moment during swimming, so the assumptions and
the expression of drag force would make us overlook some information
of swimming dynamics. It is important to observe the dynamics
of the propulsive and drag forces during swimming quantitatively and
continuously, because it would lead to better discussion of the swimming
technique and performance.
In the present study, the drag force, which is changing during front
crawl swimming, was quantified with a methodology that is according
to the equation of motion (Eq.2) to discuss the dynamics of front crawl
during swimming quantitatively and continuously, because it wo
discussion of the swimming technique and performance.
In the present study, the drag force, which is changing d
swimming, was quantified with a methodology that is according
motion (Eq.2) to discuss the dynamics of front crawl swimming. T
study were to suggest a methodology to quantify the drag force d
swimming. The purposes of the study were to suggest a methodology to
swimming, and to compare the drag force between an elite (a com
quantify the drag force during front crawl swimming, and to compare
and a non-elite (a triathlete) swimmer.
the drag force between an elite (a competitive swimmer) and a non-elite
(a triathlete) swimmer.
METHODS
METHODS The subjects were a well-trained male competitive swimmer and a m
The profile subjects of were the a well-trained subjects is male shown competitive in Table swimmer 1. The and subjects a male were asked
triathlete. crawl The using profile arms of the only subjects in a swimming is shown in Table flume, 1. The which subjects was set the flow
were m/s. asked In to the swim experiment, the front crawl the pressure using arms distribution only in a swimming on swimmer's hands
flume, the which hands was and set the position flowing velocity of the at umbilicus 1.3 m/s. In the were experiment, measured during the
the pressure distribution on swimmer’s hands, the orientation of the
hands Table and 1. the Characteristics position of the umbilicus of the were subjects. measured during the trial.
Bes
Table Subject 1. Characteristics of the Height subjects. [m] Weight [kg] Age [yrs]
100
Best record for
Subject Competitive Height [m] Weight [kg] Age [yrs]
1.79 74.0 100m-Fr. 22.4 [sec] 49.6
swimmer
Competitive swimmer 1.79 74.0 22.4 49.6
Triathlete 1.70 1.70 68.0 68.0 22.7 82.022.7
82.0
Twelve small pressure sensors, 6 mm diameter and 0.7 mm thick, (PS-
05KC, Kyowa, Twelve Japan) small were pressure attached on sensors, the swimmer’s 6 mm both diameter hands. The and 0.7 mm
attaching Kyowa, positions Japan) were were the palmar attached and dorsal on the sides swimmer's at the metacarpo- both hands. The a
phalangeal were the (MP) palmar II joint, and the middle dorsal point sides of at MP the III metacarpophalangeal and IV joints, and (MP) I
MP point V joint of (Fig. MP 1). III The and pressure IV joints, values were and recorded MP V at joint 500Hz (Fig. to 1). The pre
calculate recorded the hydrodynamic at 500Hz to force calculate Fhand exerted the hydrodynamic on the swimmer’s hands force Fhand exerted
using hands the following using the equation, following equation,
3
hand ∑
i=
1
( p − p )
F = A w
Eq.3 , ,
hand
i
palm i
dorsum i
where where A Ahand was the plane area of the hand. The index i indicates a po
hand was the plane area of the hand. The index i indicates a position
pressure to attach sensor, the pressure that sensor, is i = that 1 is is MP i = 1 II is joint, MP II 2 joint, is the 2 is midpoint the of MP II
midpoint 3 is MP of MP V joint. III and The IV joints ppalm and and 3 is pdorsum MP V joint. were The the ppalm measured and pressure
pdorsum dorsal were sides the measured of the hand, pressure respectively. on the palmar The and dorsal wi is the sides weight of of divide
the sensor’s hand, respectively. position, The and wi is it the was weight defined of divided as w1
area = w3
on = the 0.25 each and w2 = 0.5 in
sensor’s And position, it was and assumed it was defined that as the w1 direction = w3 = 0.25 of and the w2 = hydrodynamic 0.5 in forc
the
perpendicular
present study. And
to
it
plane
was assumed
of the
that
hand.
the direction of the hydrodynamic
force on a hand was perpendicular to plane of the hand.
Figure 1. A photograph of a pressure sensor (top) and the positions to
be attached the pressure sensors on the palmar and dorsal sides of a left
hand (bottom). The sensors were also attached on the right hand of the
swimmer in a similar position as the illustration.