Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
Joint Torque Request for Different Fin Uses
Gouvernet, G. 1,2 , rao, G. 2 , Barla, c. 1 , Baly, l. 1 , Grélot, l. 2 ,
Berton, e. 2
1 Oxylane Research, Lille, France
2 Institut des Sciences du Mouvement “E.J. Marey”, Marseille, France
The purpose of the present study was to examine the joint torques of
different fin swimming activities using different fins. Three different fin
uses were in focus: body-board, swimming, and snorkelling. Inverse dynamics
was used to estimate the joint torque of the lowers body joints
(knee and hip). For each practice we recorded the three-dimensional
kinematics with underwater camcorders. Apart from the kinematics inputs,
the forces and torques were measured by a robot which reproduced
mean kinematics of each practice and measured the forces and torques
components at the ankle. Thus, joint torques was measured at the ankle
and computed at the knee and hip joints. Joint torque pattern and peak
values differed for the ankle and knee joints but were not statistically
different at the hip whatever the practice. This method allows to measure
torques and forces on ankle and in this way precisely quantify the effect
of fin blade on human joints.
Key word: swimming-fin, Fin, Muscular request, snorkelling, Bodyboard
IntroductIon
Depending on the fin sport, swimmers expectations are not the same
(acceleration, endurance, or muscular gain). Therefore, fin design with
a specific shape and material has been designed for each specific sport.
For the last few years, sophisticated numerical model have enabled
for modelling propulsive and drag forces for a swimmer without fins.
The numerical model (SWUM) of Nakashima (2007) considers a fullbody
musculoskeletal model guided by different kinematics of swimming
styles (crawl, breast) and compute global swimming forces. But
this last model regards segments as rigid bodies, and the fin blade cannot
be simplified as rigid part. Thus, this previous model can not be used to
quantify the effect of a deformable fin blade.
Moreover, at the same speed, swimming with a large and stiff fin
blade requires less energy than with a short and flexible fin (Zamparo
2006). So, fin structure (shape and stiffness) entails a modification of fin
forces on foot and consequently of the energetic expenditure. The aim of
this study was thus to investigate the influence of different fin types on
joint torques during fin swimming activities.
Methods
In order to assess joint torque, an inverse dynamic model is used where
joint kinematics and hydrodynamics fin forces have to be described for
each activity.
Mean kinematics of each fin swimming activities were determined
from experimentation. Six male and 2 female skilled participants of all
activities were asked to practice the three activities in usual conditions.
Subject’s average (±SD) body mass, stature, and age were respectively
71±7.2 kg, 1.73±0.13 m, and 27±3.2 years. For swimming, subjects swim
holding out their arms on a board, and their heads in water. Bodyboarders
were told to adopt the same velocity as when they go to the
reach, with their chests lifted-up and their elbows on the body-board
flexed at 90°. And for snorkelling, they practise with masks and snorkel,
arms along the body, swimming only with legs. Each subject swims 2
pool lengths for each of the 3 practices. For each practice, standard DE-
CATHLON fins were used (Figure 1).
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Figure 1. Fins for body-board (a), swimming (b), and snorkelling (c).
Eleven markers were positioned on the left lower limb. The tri-dimensional
motion of lower limbs was simultaneously recorded by four
cameras, on full frame with 800x650 pixels at 50 Hz (DALSA Falcom
1.4M100). A sufficient calibration space (4m long) was placed on
the swimming pool. The picture definition allowed a good precision
of tracking. The three-dimensional positions were computed by the
DLT method (SIMI Motion Systems GmBh, Germany ). Data were
smoothed using a Butterworth lower pass filter at 6Hz. During each
swim, three cycles were selected. The cycles were cut at the higher position
of the subject’s foot. Then, the cycles were averaged to obtain a
representative kinematical cycle per subject per and swimming activities
(body-board, swimming, or snorkelling).
For each activity recorded, the foot motions averaged over the subjects
were reproduced using a custom-made robot. This twice-fin robot
reproduces the kinematics of the two feet by velocity control. Ankle
angle and vertical kicking were controlled (Figure 2). Also, the distance
of the robot from the water surface could be adjusted, in order to reproduce
the good kicking depth too. The foot motion on sagittal plane was
used as an input parameter of the robot. A waterproof six-component
sensor is located on the foot form of the robot, at the same position as
the ankle joint; in this way forces and torques produced by fin on foot are
measured. Moreover, the robot moved forward at the velocity measured
in each fin swimming activities. Thus, sagittal ankle motions reproduced
the foot motion of each activity with a matching velocity. This simulation
of fin swimming activities allowed us to consider measured forced
as close to real forces encountered during swimming as possible.
Three-dimensional force and torque measurements were made on
the foot robot which reproduced mean motion of each activity. Inverse
dynamics computations were carried out to estimate the threedimensional
net forces and torques at the knee and hip joints. Net joint
moments were estimated taking into account gravity, inertial body parameters,
as well as Archimedes thrust (FA=ρ water .V.g), the volume (V)
being assessed as a function of body mass and segment density (Zatiorsky
1990). This force was applied at the segment centre of mass.
Both swimming (frequency, amplitude and depth of the kick), and
muscle torque variables were analyzed.