Cause-Effect ~ Total Body Level
 Total Body Center of Mass (TBCM)
 Free Body Diagram (FBD)
 Mass-Acceleration Diagram (MAD)
 General global coordinate system (up & to the right, (+) )
 Center of Pressure (COP)
 Ground Reaction Forces (GRF)
 Position of TBCM relative to COP, and influence on
GRF magnitude and direction
 Net Force (F)
 Body segment parameters
 Gait analysis parameters
 Course Reader: p. 7-11, 21-28, &Ch 5
Total Body Center of Mass (TBCM)
• Balance point of an object
• Center of an object of uniform
density
• Position is dependent upon
relative mass distribution &
segment orientation
• Can be located outside the
body
• During human gait, estimated
to be around the hip/pelvis &
between base of support (M-L)
• Position is controlled relative to
COP to change the orientation
of GRF - dependent upon the
mechanical objective of the
task
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Glut Max
SM/ST
ground
Draw the FBD for:
a) Forces acting on the runner
b) Forces acting on the ground
F h = m*ah
F v = m*av
Free Body Diagram
(FBD)
Mass Acceleration Diagram
(MAD)
mav
mah
BW
Fh
Fv
Global Coordinate System
TBCM location is determined by the relative mass
distribution and segment orientation
CMx
Foot CMx
CMx
Foot CMx
Note any between-athlete
differences in:
• stance thigh angle;
• swing leg position;
• trunk orientation;
• arm swing position;
that may contribute to the noted
difference in CM position relative
to COP.
Each Dive Can Be Separated Into Phases, Each with it’s Own Goal
Loading
Tipping
Pushing
Flight
During the Tipping phase, the center of mass is
positioned relative to the feet according to the
dive. The position of the CM relative to the force
generated during the Push phase will determine
rotation (angular momentum) during flight
Entry
preparation
Controlling shank motion to re-orient TBCM position
relative to COP during a “quick first step”
“push”
“tip”
ground
Draw the FBD for:
a) Forces acting on the runner
b) Forces acting on the ground
Calculating individual segment CM location
Segment CM location coordinates (x, y)
Xcm = xprox - (segment length x) * CM% from proximal
Ycm = yprox - (segment length y) * CM% from proximal
Total Body Center of Mass location coordinates (x, y)
X tbcm = (mixi) / TB Mass
Y tbcm = (miyi) / TB Mass
EX: segment CM calculation
Body Segment Parameters for calculating TBCM location
From: de Leva P. "Adjustments to Zatsiorsky-Seluyanov's segment inertia parameters." J Biomechanics, 29(9), p 1223-30.
Se gm e nt
Head
Trunk
Upper Arm
Forearm
Hand
Thigh
Shank
Foot
Proxim al Endpoint Dis tal Endpoint
vertex
C7
C7
hip jt center
shoulder jt center
elbow jt center
elbow jt center
w rist jt center
w rist jt center
tip 3rd finger
hip jt center
knee jt center
knee jt center
ankle jt center
heel
toe
Se gm e nt M as s (% TB M as s )
Fe m ale
M ale
6.68
6.94
42.57
43.46
2.55
2.71
1.38
1.62
0.56
0.61
14.78
14.16
4.81
4.33
1.29
1.37
99.99
100.00
CM Pos ition (% le ngth)
Fe m ale
M ale
58.94
59.76
49.64
51.38
57.54
57.72
45.59
45.74
74.74
79.00
36.12
40.95
44.16
44.59
40.14
44.15
Body Segment parameters for females (BM=61.9 kg, Height=173.5 m) and males (BM=73.0 kg, Height=1.741 m)
Segment masses are relative to total body mass
Segment CM positions are ref erenced either to proximal or cranial endpoints (origin)
Gait Analysis Parameters
• Events - define phases
Walking Gait
– Foot-Strike, Toe-Off
• Phases - fall between
adjacent events
(e.g. single support, double
support, swing, non-support)
• Step length (m)
• Step rate (/s)
Walking vs. Running Gait
• Walking includes doublesupport phase
• Running includes flight-phase
/ non-support phase
• Average Velocity
(SL * SR)
Running Gait