Biomech_DYN_2010 [Compatibility Mode]

Biomechanics
Dynamics
J. Paulo Vilas-Boas, Ph.D
Leandro Machado, Ph.D
Filipa Sousa, Ph.D
jpvb@fade.up.pt; lmachado@fade.up.pt; filipas@fade.up.pt
Dynamics
Dynamics
Forward dynamics:
∑ F = ma
F
Forward dynamics:
a
Inverse dynamics:
x
••
x
∑ F = ma
a
Force and pressure transducers:
- Strain gauges
••
mx = ∑F
F
F
- Dynamometers
- Force Plates
- Isokinetic dynamometers
- Pressure transducers
- Isometric dynamometers
- Dynamic dynamometers
1
Dynamics
Force transducers
Strain gauges
Dynamics
(Bartlett, 1997)
Force transducers
Force plates
Force and torque components
which act on the performer
Dynamics
Dynamics
Force transducers
Force plates
Force plates
Data examples
Vertical RF
Resultant vector
Acceleration
Horizontal RF
Deceleration
Pronation
CP migration
Lateral-medial RF
Supination
Ground contact forces in walking (3D)
(from Amadio et al., 1996)
2
Dynamics
Force plates
Dynamics
Force plates
Naide Gomes - componente vertical 3 passagens
Naide Gomes - componente médio-lateral 3 passagens
12
3
10
2
Força / Peso
Força / Peso
8
6
4
1
0
2
0
-1
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0
20
40
60
80
100
t norm
t (s)
Naide Gomes - componente vertical 3 passagens
Naide Gomes - componente antero-posterior 3 passagens
12
1
0
10
-1
Força / Peso
Força / Peso
8
6
4
-2
-3
-4
-5
2
0
-6
0
20
40
60
80
100
-7
0
20
40
t norm
Force plates
Dynamics
60
80
100
t norm
Force plates
Dynamics
Nelson Évora - componente antero-posterior 4 passagens
4
0
t apoio =paulo1
0.167
s
Paulo
-2
componente médio-lateral
1
0
0
20
40
60
80
3
2
1
100
3
-1
-2
-3
0
-0.5
-4
0
-1
Nelson Évora - componente médio-lateral 4 passagens
força normalizada
4
t norm
Nelson Évora - componente vertical 4 passagens
força normalizada
0.5
-6
15
paulo1 Paulo
componente antero-posterior
1
5
-4
-8
paulo1 Paulo
componente vertical
6
força normalizada
Força / Peso
2
0
20
40
60
tempo normalizado
80
-5
100
Vertical:
Máx: 5.95 * Peso = 4422.2 N, aos 0.025 s
0
20
40
60
tempo normalizado
80
100
-1
0
20
Antero-posterior:
Máx: 4.60 * Peso = 3419.2 N, aos 0.022 s
40
60
tempo normalizado
80
100
Médio-lateral:
Máx: 0.91 * Peso = 675.2 N, aos 0.029 s
2
marisa1 Marisa
componente vertical
4
3
2
1
0
0
20
40
60
t norm
80
100
-2
0
20
40
60
t norm
80
100
-1
-2
-3
1
0.5
0
-4
0
-1
força normalizada
-1
componente médio-lateral
1.5
0
5
0
marisa1 Marisa
componente antero-posterior
1
6
força normalizada
5
1
força normalizada
Força / Peso
Força / Peso
t apoio =marisa1
0.154
s
Marisa
7
10
0
20
40
60
tempo normalizado
80
Vertical:
Máx: 7.00 * Peso = 3797.0 N, aos 0.013 s
100
-5
0
20
40
60
tempo normalizado
80
100
Antero-posterior:
Máx: 4.38 * Peso = 2376.6 N, aos 0.015 s
-0.5
0
20
40
60
tempo normalizado
80
100
Médio-lateral:
Máx: 1.17 * Peso = 636.4 N, aos 0.022 s
3
Dynamics
Force plates
Force and torque components
which act on the performer
(Bartlett, 1997)
Dynamics
Force plates
Force plate
transducers
They detect force and converts
(transduce) it into electrical signal
Strain gauges
Vectorial expression of forces
with location (and migration)
of the centre of pressure
No insight on force distribution
along the contact surface
Used for foot strike patterns, balance, input for inverse dynamics
Whole-body measurements
Material which electrical resistance
changes with its deformation (strain)
- sensitive to temperature
- less expensive and easier to install
- more suitable for statical situations
Piezoelectric
They rely on the development of a electrical
charge by a crystal (e.g. Quartz) when subject
to a force
- drift disadvantage for static analysis
Dynamics
Force plates
Operational characteristics:
- high sensitivity
- low force detection threshold
- high linearity (a)
- low hysteresis (b)
- low cross-talk
- no cable interference, electrical
inductance, temperature and humidity
variations
- good dynamic response (c)
- low amplitude ratio
- low phase lag
4
Dynamics
Dynamics
Force plates
Force plates
Data examples
Data examples
Vertical GRF in standing vertical jump
(Bartlett, 1997)
Different surfaces
Different foot strike
Different shoes
Ground contact forces in running (vertical component).
(Adapted from Nigg, 1986, quoted by Bartlett, 1997)
Dynamics
Dynamics
Force transducers
Force transducers
Force plates
Dynamometrical parameters
a) ∆t
Force plates
b) Fy1
c) ∆t Fy1
d) Fy min
e) ∆t Fy min
F
f) Fy2
g) ∆t Fy2
Gaitway System (Kystler)
h) Deflection
i) Increment
j) Fx min
k) ∆t Fx min
l) Fx max
m) ∆t Fx max
n) Force Gradient 1 (FG = b/c)
o) Force Gradient 2 (FG = f/(g-e))
p) Vertical Impulse (Imp Y)
q) Negative Impulse (ImpN)
r) Propulsive Impulse (ImpP)
s) Impulses relationships (Imp Rel)
t
Based on Soares, R. (2005)
5
Dynamics
Dynamics
Force transducers
Force transducers
GRF vertical component (Fy)
Force plates
(bw)
Values of the first peak (PC)
Force plates
1st Vertical Peak
Slope (gradient)1
Intermediate minimal force
2nd Vertical Peak
75 ms vertical impulse (passive)
Total vertical impulse
Support time
18
16
14
12
10
8
6
4
2
0
Walking
Running
High J
Long J
Triple (step)
Walking Running
High J
Long J
Triple
(step)
Double support time
Adapted from BAUMMAN & STUCKLE (1980)
Based on Soares, R. (2005)
Statics
Dynamics
Force plates use for balance evaluation
Force plates and pressure transducers
Stabilogrametry
Rear foot
0%
15%
Midfoot
30%
0%
15%
Forward foot
30%
0%
15%
30%
Rambling and trembling assessment for neuro-motor balance analysis
Gait dynamometry of pre-pubertal children with different dorsal extra-loads
(from Vilas-Boas et al., 2002)
6
Dynamics
Pressure transducers
Dynamics
Pressure transducers
- Foot area of contact
- Qualitative assessment
of pressure
- Anthropometry of the foot
Based on Soares, R. (2005)
Dynamics
Data processing
Dynamics
Pressure transducers
- 2D “colour coded” displays
- 3D wire frame displays
- Force, maximal pressure and contact area
- Pressure-time integral for all regions of the foot
- Centre of pressure path
7
Dynamics
Dynamics
Capacitive pressure transducers
Conductive pressure transducers
N
(Bartlett et al, 1991)
Also a 3 layer construction :
A matrix of rows and columns of
conducting material, which sandwich a layer of resistive material
- Not sensitive to temperature
- Much thinner and inexpensive
3 layer construction:
A matrix of rows and columns of
conducting material, which sandwich a layer of capacitive (dielectric) material
r x c = number of capacitors
EMED
insoles
85, 170 or 256 sensors
- Calibration much more linear
but instable
- Flexible but fragile
AMTI conform (Derrick and Hamill, 1992)
F-Scan
insoles
100Hz, 50Hz and 20Hz
Accuracy = 5%; Hysteresis = 3%; Peak up to 1270 kPa
- Can be cut to foot size
960 sensors (5.1 mm2)
100Hz
Peak up to 1035 kPa
Dynamics
Dynamics
Piezoelectric pressure transducers
Pressure transducers
Also a 3 layer construction :
A matrix of rows and columns of
conducting material, which sandwich a layer of resistive material
- Sensitive to temperature
- Thick (3 to 4 mm) and expensive
- Each transducer requires individual connections
- Flexible
Developed by Henning et al, 1993)
Platforms
Insoles
Hand grip
Other transducers
499 sensors (23 mm2)
not
commercially 200 Hz
available
Accuracy = 2%; Hysteresis = 1%; Peak up to 1500 kPa
8
Dynamics
Pressure transducers
Dynamics
Pressure transducers
Dynamics
Pressure transducers
Dynamics
Pressure transducers
9
Dynamics
Data processing
Dynamics
Pressure transducers
Dynamics
Pressure
transducers
10