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 aTIFF (Uncompressed) decompressor

are needed to see this picture.

Glut Max

SM/ST

Draw the FBD for: a) Forces acting on the runnerb) Forces acting on the ground

ground

FFvv

FFhh

BWBW

Free Body Diagram(FBD)

Mass Acceleration Diagram(MAD)

F h = m*ah

F v = m*av

mamahh

mamavv

Global Coordinate System

CMxCMx

Foot CMxFoot CMx

CMxCMx

Foot CMxFoot CMx

TBCM location is determined by the relative massdistribution and segment orientation

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.

Loading

Each Dive Can Be Separated Into Phases, Each with it’s Own Goal

Tipping Pushing FlightEntry

preparation

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

“tip” “push”

Controlling shank motion to re-orient TBCM position

relative to COP during a “quick first step”

Draw the FBD for: a) Forces acting on the runnerb) Forces acting on the ground

ground

Calculating individual segment CM location

Segment CM location coordinates (x, y)Xcm = xprox - (segment length x) * CM% from proximalYcm = yprox - (segment length y) * CM% from proximal

Total Body Center of Mass location coordinates (x, y)X tbcm = (mixi) / TB MassY 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.

Segment Proximal EndpointDistal Endpoint Female Male Female Male

Head vertex C7 6.68 6.94 58.94 59.76Trunk C7 hip jt center 42.57 43.46 49.64 51.38Upper Arm shoulder jt center elbow jt center 2.55 2.71 57.54 57.72Forearm elbow jt center wrist jt center 1.38 1.62 45.59 45.74Hand wrist jt center tip 3rd finger 0.56 0.61 74.74 79.00Thigh hip jt center knee jt center 14.78 14.16 36.12 40.95Shank knee jt center ankle jt center 4.81 4.33 44.16 44.59Foot heel toe 1.29 1.37 40.14 44.15

99.99 100.00

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 massSegment CM positions are referenced either to proximal or cranial endpoints (origin)

Segment Mass (% TB Mass) CM Position (% length)

Gait Analysis Parameters

• Events - define phases– 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 double-

support phase• Running includes flight-

phase / non-support phase• Average Velocity

(SL * SR)

Walking Gait

Running Gait