Download comparison of subacromial volume in shoulder impingement test

WAVELET-EMG-ANALYSIS OF SHOULDER MUSCLES DURING A POWER BACKWARD
GIANT SWING ON HIGH BAR
Frère J. 1, Göpfert B. 2, Slawinski J. 3, Tourny-Chollet C. 1
CETAPS laboratory EA 3832, Faculty of Sports Sciences, University of Rouen, France, 2 Laboratory of
Biomechanics & Biocalorimetry, University of Basel, Switzerland and 3 Research Center for Expertise, Scientific
Department of Team Lagardère, Paris, France
1
Abstract – The execution of a Power Backward Giant
Swing (PBGS) mainly involved the shoulders
muscles. The aim of this study was to analyse the
EMG activity of shoulder muscles during a PBGS.
Eight shoulder muscles were recorded while the
wavelets transformation was used to analyze the raw
EMG signal. The PBGS was divided into four phases
of 90°. The analysis was divided into a qualitative
approach from the intensity pattern of the muscles
and quantitative approach from the peak of
intensity in each phase of the PBGS. Both
approaches indicated that small muscles were
recruited when tensile loads on the shoulder were
low, while large muscles were activated during the
most demanding phases before bar release.
axis of the bar and covered a sufficient range to
record the entire body of the gymnast during the
movement. A marker placed at the femoral greater
trochanter was used to identify key events to
define the phases. The PBGS has been analyzed
according to the standard of a previous study [1],
where the movement has been divided into four
phases corresponding to four areas of 90° (Figure
1).
1. INTRODUCTION
During a Power Backward Giant Swing (PBGS),
the energy interaction between the gymnast and
the high bar resulted in a significant increase of the
gymnast’s energy allowing dismounts and releaseregrasp elements [1]. Simulations by forward
dynamics of the PBGS were using a shoulder joint
modeled by a parallel spring and damper [2, 3].
Thus, it is commonly accepted that the muscular
actions around the shoulder joints are the most
important to achieve a PBGS, especially just
before the bar release [1, 4]. However, the
shoulder muscles activations during such
movement are currently lacking. This study is
based on the EMG recording of shoulder muscles
and aims to analyze their activation during the
different phase of a PBGS. It is expected that
muscles activations increased significantly in the
most demanding phases for the shoulder joint.
2. MATERIALS AND METHODS
Six gymnasts with a national level participated in
this study and performed five times a PBGS which
corresponds to a complete and accelerated swing
around the high bar to prepare a dismount. Finally,
28 PBGS have been recorded by a video camera in
the sagittal plane with a sampling frequency of 50
Hz. The camera was placed along the longitudinal
Figure 1: Averaged MMP of the group during a
PBGS.
During the experiment, the gymnast wore an
embedded EMG device (Biovision). The surface
EMG recordings were made using self-adhesive
Ag/AgCl pairs of electrodes (SENIAM-Standard).
The activity of eight muscles of one side was
recorded (Figure 1). The non-linear scaled
wavelets transformation of the EMG signal (WTEMG) was performed with a MATLAB® toolbox
(http://atoc.colorado.edu/research/wavelets/) [5].
The EMG signal processing was divided into two
steps, including a qualitative approach and a
quantitative approach. The first step was the
creation of an averaged multi muscle pattern
(MMP) from the intensity pattern of each muscle
during a PBGS. This averaged MMP allowed a
qualitative analysis on the times and durations of
muscular activation. The quantitative approach
was done from the WT-EMG, in which the total
intensity was calculated by summing the intensity
of all the wavelets [6]. For each muscle and in
each phase of the PBGS, the peak value of the
total intensity was recorded to determine the
degree of muscle activation. The values were
subsequently averaged for the whole group. The
conditions for the use of parametric tests being not
affected, the Wilcoxon rank test was used for
inter-phases comparisons of EMG intensities. The
Kruskal-Wallis was used to test the effect of
phases on the signal intensity. The threshold of
significance was set at P<0.05.
3. RESULTS
The Figure 1 is reflecting the qualitative approach.
Except the triceps brachii muscle which has a
relative constant activity throughout the PBGS,
two groups of muscles present an “as one”
activity. The both parts of the deltoideus, the
trapezius, and the infraspinatus muscles form a
group mainly active in the two firsts phases, while
the second group containing the biceps brachii, the
pectoralis major, and latissimus dorsi muscles is
mainly active during the two lasts phases. The
Figure 2 is reflecting the quantitative approach.
With the exception of the infraspinatus muscle, all
the muscles undergo a significant phases effect
(P<0.05) on the peak of total intensity during a
PBGS. The latissimus dorsi and pectoralis major
muscles appear to be solicited in synergy since the
total intensity of these two muscles is significantly
lower (P<0.05) in phase 2 of the PBGS relative to
the phases 1 and 4 whereas deltoideus pars
clavicularis and spinalis, and trapezius muscles
have a significant opposition between the total
intensity of phases 1 and 2 and that of phases 3
and 4.
4. DISCUSSION AND CONCLUSIONS
All the muscular activities increased, except the
triceps brachii muscle, when the gymnast reduced
his gyration radius to improve his angular velocity
around the bar. Indeed, Holvoet et al. [4]
calculated that along the PBGS, the effort on the
bar was always in traction, with the highest values
in the two lasts phases before bar release. In
consideration of the results of this previous study
associated with EMG data, it appears that the
muscles faced up to tensile loads to stabilize the
scapulo-humero-thoracic joint complex. When the
handstand position on the bar is approaching the
deltoideus (both parts), infraspinatus, and
trapezius muscles group was mostly recruited. Due
to small traction on the bar in these two firsts
phases, small and scapular muscles were recruited.
During the two lasts phases, the traction on the bar
increased, involving the activation of larger
muscles, such as pectoralis major and latissimus
dorsi
muscles.
This
synergy
latissimus
dorsi/pectoralis major was therefore specific to
brachiation, in which the latissimus dorsi muscle
revealed its anti-gravitational function and
generated the humeral extension while the
pectoralis major muscle had a stabilizing action on
the shoulder joint complex.
The functions defined in this wavelet-EMGanalysis of shoulder muscles were consistent with
the shoulder joint model already used for
simulations [2, 3] and agreed with previous
biomechanics findings about the most demanding
phases of the PBGS [1, 4]. Also, the strengthening
of large muscles, such as latissimus dorsi and
pectoralis major, is of primary importance to
perform powerful brachiation movements.
5.
Figure 2: Averaged normalized peak of intensity
among the four phases of the PBGS.
REFERENCES
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Biomech. 31:1083-1092.
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[3] Sheets A.L. & Hubbard M., (2009), J.
Biomech. 42:1685-1691.
[4] Holvoet P. et al., (2002), Sci. Sports. 17:26-30.
[5] Torrence C. & Compo G.P., (1998), Bull. Am.
Meteorol. Soc. 79:61-78.
[6] von Tscharner V., (2000), J. Electromyogr.
Kinesiol. 10:433-445.