Transcript motion capture

BIOMECHANICS
Motion Capture
The mean values of max moment of force
MUSCLE
GROUP
X [Nm]
Wojtek
M
260
241
F
180
M
590
F
420
M
145
F
70
EX SH M
110
F
56
M
90
F
50
M
60
F
30
FL T
EX T
T – trunk,
El – elbow,
SH – shoulder,
Fl – flexion
EX extention
FL SH
FL El
EX El
Lucia
Li-Ting
Samuel
Andrew
504
L 143/
R 133
L 93,5 /
R 105
L 81 /
R 76
L 93,5 /
R 78,6
L 92,7 /
R 88,5
L 58 /
R 77
L 44,2/
R 48,6
L 57,5 /
R 59,2
L 38,2/
R 37
The mean values of hand grip
HAND
GRIP
X [N]
Wojtek
M
600
L 616 /
R 639
(20 sec)
endurance
F
endurance
350
Maria
Lucia
L 322/
R 380
R 346
(145 sec)
Endurance = fatigue resistance
Karolina
R 380
(96 sec)
Conclusions
 To prevent from loose of your strength try to avoid extreme
joint angles! (muscle will be close to its limit – see figure).
 For the slow movements of large amplitudes use arm, while the
fast ones of small amplitudes are best suited for the fingers!
 Practice should focus on complete repetitions of the whole skill
performed at submaximal speeds – improvement should occur
with many repetitions, while gradually increasing speed
(segmental interaction – acceleration of proximal segment (arm) ->
acceleration of the distal segment appears (hand with sticks).
 Listen to your body – there is a lot of signals coming from it
(receptors in the skin, muscles, joints, tendons), don’t ignore
them!
Muscle force vs. lenght of muscle
daily activities
Optimal length of the muscle
PROPRIOCEPTIVE SYSTEM
is responsible for collecting information
about the body itself: from within the body,
largely from the muscles and joints.
Skin receptors
Muscle spindles
Golgi Tendon Organs
4 degrees of freedom
Kopar
240 degrees of freedom
Degree of freedom –movement in a plane.
Human body = a system of body links which form
one or more kinematic chains.
 First PHOTOGRAPHY second part of XIX century =
a turning point in refers to human body movements.
 Photos of running horse (1872), E. MUYBRIDGE applied the
techique of sequential photography.
The next step was to take lots of pictures
by means of 1 camera - E.J.MAREY,
that initaited cinematography.
3D registration of movement by Braune & Fisher (XIX/XX cent.)
 Motion tracking or motion capture started as
a photogrametric analysis tool in biomechanics
research in the 1970s and 1980s, and
expanded into education, training, sports and
recently computer animation for cinema and
video games as the technology matured.
VICON
A performer wears markers
near each joint to identify
the motion by the positions
or angles between the
markers.
passive
marker
Vicon System
 Vicon automatically
records 3D location
of markers as points
and in very precise
way determines their
position in space
based on the data
achieved from
2D video picture.
JOINT ANGULAR CHANGES/ MUSCLES LENGHT CHANGES
Motion capture
 To register the movement - markers should be
located in the essential (from animating point
of view) places on the actor’s body.
Spatial trajectory of foot movement in the sequency
high legs techniques and stability evaluation based on COM
of
Archer
Hoovering
Race walker
Gollum’s body - about 300 muscles.
-> normal skeleton and system of the muscles;
-> motion capture recordings were done - Andy was wearing suit
covered with small points. He behaved then as if he was Gollum.
->
Andy Serkis - Gollum
 The biggest challenge was
Gollum’s face. Side by side shots
were shown with Andy and Gollum
showing exactly the same facial
expressions and speech
expressions.
 - Gollum is probably the most
similar to the real actor digital
creature, that ever appeared in
the film – said Jackson - the film
director.
skull caps fitted with a tiny camera
Electromyography (EMG)
EMG is a very valuable tool in measuring skeletal muscle
electrical output during physical activities.
Electromyography
= bioelectric activity of the muscles
Skin surface electrodes
 Due to their non- invasive character in most cases surface
electrodes are used in kinesiological studies.
 For deeper muscles (covered by surface muscles or bones) finewire or needle electrodes are inevitable. A free selection of
any electrode type is supported by an EMG – (pre-) amplifier.
The selection of an electrode type strongly depends on the given
investigation and condition.
General considerations
 The quality of an EMG measurement strongly depends on a
proper skin preparation and electrode positioning.
 The recommendations for skin preparation:
 to shave the patient if the skin surface at which the electrodes
have to be placed is covered with hair.
 to clean the skin with alcohol and allow the alcohol to vaporise so
that the skin will be dry before the electrodes will be placed.
The Motor Unit
 The smallest functional unit to describe the neural control of the
muscular contraction process is called a Motor Unit.
 Single motorneuron & muscle fibers it innervates
Raw EMG signal
The relationship between EMG input
and force output
 EMG activation is the preliminary condition for any force
development and one can expect a very close relationship
between both measures. Indeed, there is a very high
correlation between both parameters.
 Muscle Fatigue
 The surface EMG can also be used as measure of
muscle fatigue and recovery.
 A major point of interest is the measure of muscle
fatigue along with the electromyography.
 The change in median frequency of power spectrum
density is one of the factors that can be used as an
indicator of muscle fatigue (De Luca, 1993).
Force platform =? weight scale
Ground Reaction Force
Force platform is used to measure ground reaction force on
the base of Newton’s third law: law of reciprocal actions.
Reaction force
‘to every action there is always
an opposed equal reaction’
What does it mean?
the ground is coming back up to you and supporting you with a force equal to
that of gravity.