Biomedical Engineering Reference
In-Depth Information
2
Methods
2.1
Sample
Twenty-four subjects (n
24) divided in two groups were studied: the throwers
group with three volleyball players (height
D
D
181
˙
4,7 cm; age
D
22
˙
4,0 years;
body
mass:
75
˙
7,6
kg)
and
six
handball
players
(height
D
184
˙
3,7
cm;
age
D
22
˙
0,9 years; body mass
D
81
˙
5,6 kg); and the non-thrower group
with 12 non-thrower athletes (height
D
176
˙
4,7 cm; age
D
26
˙
2,9 years; body
mass
D
73
˙
7,5 kg).
2.2
Kinematic Proceedings
Humeral and scapular 3D positions were recorded by means of a 6DOF electromag-
netic tracking device (Hardware: “Flock of Birds system” Ascension Technology;
Software: Motion Monitor v 7.0) which allowed simultaneous tracking of four
sensors at a sampling rate of 100 Hz per sensor. This system allows the registration
of the position and orientation of the sensors in space always when they are inserted
in an extended electromagnetic field.
The static accuracy of these sensors with an Extended Range Transmitter is up
to 0.76 cm RMS/0.5 degrees RMS at a 1.52 m distance from the transmitter. The
static resolution is 0.08 cm/0.1 degrees RMS at 1.52 m from the transmitter. On data
collection a four sensors setup was used. Thorax sensor was attached over T1 using
double faced tape assuring its fixation. The arm sensor, placed just below the deltoid
attachment, by mean of a cuff firmly adjusted to the arm. Finally the scapular sensor
was attached to the superior flat surface of the acromion process, using the same
kind of tape (Table
1
).
Tabl e 1
Bony landmarks
used on the definition of the
local coordinate system of the
thorax, scapula and humerus,
according with Wu et al. [
50
]
Segment Bony landmark Abbreviations
Thorax T8 spinous process T8
Xiphoid process of the sternum PX
C7 Spinous process C7
Incisura Jugularis of the sternum IJ
Scapula Angulus acromialis AA
Trigonum Spinae Scapulae TS
Angulus Inferior Scapulae AI
Humerus Epicondylus medialis EM
Epicondylus lateralis EL
Glenohumeral rotation centre
a
GH
a
Estimated by motion recordings, calculating the pivot point of
instantaneous helical axes of GH motion [
51
,
52
]
