Biomechanics and Medicine in Swimming XI

The Acute Effect of Front Crawl Sprint-resisted
Swimming on the Direction of the Resultant Force of
the Hand
Gourgoulis, V. 1 , Aggeloussis, n. 1 , Mavridis, G. 1 , Boli, A. 1 ,
toubekis, A.G. 2 , Kasimatis, P. 1 , Vezos, n. 1 , Mavrommatis, G. 1
1 Democritus University of Thrace, Komotini, Greece
2 Kapodistrian University of Athens, Athens, Greece
The aim of the study was to investigate the acute effect of front crawl
sprint-resisted swimming on the direction of the resultant force of the
hand. Five female swimmers swam 25 m with maximal intensity with
and without added resistance. The underwater motion of the hand was recorded
using 4 cameras (60 Hz) and the Ariel Performance Analysis System
was used for the digitization. The results showed that the magnitude
of the drag and lift forces, as well as the magnitude of the resultant force
was not modified significantly during resisted swimming. However, the
angle formed between the resultant force and the axis of the swimming
propulsion was decreased significantly in the pull phase. Thus, it could be
speculated that sprint-resisted swimming could contribute to the learning
of a more effective application of the propulsive forces.
Key words: front crawl, resisted swimming, resultant force.
IntroductIon
In front crawl swimming, the propulsive forces generated mainly from
the arms. The way swimmers use their arms to apply these forces is decisive
for effective swimming propulsion (Arellano, 1999). The resultant
propulsive force produced by a swimmer’s hand is a combination of two
types of propulsive forces: the drag force and the lift force. For effective
swimming propulsion the resultant of these two forces should be aimed,
as much as possible, in the swimming direction (Rushall et al., 1994;
Schleihauf, 2004; Toussaint et al., 2000). In addition, in front crawl
swimming, which is a stroke with alternate arm movement, it is necessary
to avoid significant deviations of the resultant force vector from
the swimming direction, since this may cause undesirable sideways and
vertical deviations of the body, increasing the resistive forces (Vorontsov
& Rumyantsev, 2000).
Moreover, it is considered that training methods such as sprintresisted
swimming where the swimmers swim against a resistance in
addition to the natural water resistance are more effective for the improvement
of the swimming performance than dry land training methods
(Girold et al., 2007; Llop et al., 2006; Williams et al., 2001). In the
past, the acute effect of sprint-resisted swimming has been investigated
in various kinematic characteristics of the stroke, such as the time of the
underwater motion of the hand, the velocity of the hand, its medial –
lateral displacements, the stroke rate, the stroke length, the stroke depth
and the swimming velocity (Maglischo et al., 1984; Maglischo et al.,
1985; Williams et al., 2001).
However, there is a lack of data regarding the effect of the sprint-resisted
swimming on the direction of the resultant force. It could be speculated
that, if during sprint resisted swimming the angle between the
resultant force vector and the axis of swimming propulsion is decreased,
then this training method could probably contribute to the learning of a
more effective application of the propulsive forces. Therefore, the aim of
the present study was to examine the acute effect of front crawl sprintresisted
swimming on the direction of the resultant force of the hand.
Methods
Five female competitive swimmers participated in the study (age: 20.4
± 6.1 years, height: 1.73 ± 0.03 m, body mass: 59.1 ± 6.67 kg, best performance
in the 100 m front crawl swimming: 62.59 ± 2.88 s). Each
swimmer swam in randomized order two trials of 25 m front crawl with
chaPter2.Biomechanics
maximal intensity. One of the trials was performed without added resistance
and the other one was performed with an added resistance. A
bowl with a diameter of 32 cm and a capacity of 6 l was used as added
resistance. The bowl was pulled by its convex side and it was tethered on
a belt, which was around the waist of each swimmer, with a 1.5 m long
elastic tube (Mavridis et al., 2006). All trials were executed using a sixbeat
kick and without breathing in the middle of the distance, where the
underwater stroke was recorded.
The underwater motion of the right hand was recorded using four
camcorders (60 Hz), which were positioned behind four stationary periscope
systems. The synchronisation of the cameras was achieved using
a LED system visible in the field of view of each camera. A calibration
frame with dimensions of 1m x 3m x 1m for the transverse (X), the
longitudinal (Y) and the vertical (Z) directions, respectively, containing
24 control points, was used for the calibration of the recorded space in
the middle of the 25 m swimming pool (Gourgoulis et al., 2008a). Before
filming, selected points were marked on each swimmer’s skin corresponding
to the acromion of the right shoulder, the greater trochanter
of the right and left hip, and four points on the right hand: the center
of the wrist, the tip of the middle finger, the index and the little finger
metacarpophalangeal joints. These points were digitized using the Ariel
Performance Analysis System (Ariel Dynamics Inc., San Diego CA,
USA) and their three dimensional coordinates were calculated using the
direct linear transformation procedure.
For a detailed description and quantification, the underwater stroke
of the right hand was divided into three distinct phases: (a) entry and
catch, (c) pull and (c) push (Chollet et al., 2000). The hydrodynamic
coefficients and the methodology presented by Sanders (1999) were
used for the estimation of the drag force, the lift force and the resultant
force of the swimmer’s hand. Moreover, the component of the resultant
force in the swimming direction, defined as the effective propulsive
force generated from the swimmer’s hand, and the angle between the
resultant force and the axis of propulsion were calculated (Gourgoulis et
al., 2008c). The stroke length, the stroke rate and the mean swimming
velocity were also calculated (Gourgoulis et al., 2008b).
For the statistical treatment of the data, the t-test for dependent
samples was used. The normal distribution and the homogeneity of variance
were verified using the Kolmogorov – Smirnov test and the Levene
test, respectively. The significance level was set as p < 0.05.
results
During resisted swimming the stroke length, the stroke rate and the
mean swimming velocity were decreased significantly (Table 1).
Table 1. Stroke length (m), stroke rate (cycles⋅s -1 ) and mean swimming
velocity (m⋅ s -1 ) during front crawl swimming with and without added
resistance.
Without
added resistance
With
added resistance
t- value
Stroke length 1.88 ± 0.07 1.28 ± 0.08 13.155*
Stroke rate 0.84 ± 0.04 0.74 ± 0.06 5.188*
Mean swimming
velocity
* p < 0.05
1.57 ± 0.09 0.95 ± 0.13 26.750*
During the pull and the push phase, the magnitude of the mean drag
force, the mean lift force, the mean resultant force and the mean effective
propulsive force, were not altered significantly, in comparison with
free swimming. On the other hand, the angle between the vector of
the resultant force and the axis of swimming propulsion was decreased
significantly during the pull phase in the resisted swimming condition.
This modification was not observed during the push phase (Table 2).
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