LS2.Lecture29.gaits

LS2.Lecture29.gaits - LS 2 Lecture 29: HUMAN GAITS...

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LS 2 Lecture 29: HUMAN GAITS Professor Daniel E. Lieberman November 15, 2010 My office hours: Tuesdays 1-2 Peabody 53 (and other times by appt )
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Today When and why did we become bipedal? How do we walk? How do we run?
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Bipedalism: key distinguishing feature of the human lineage! Australopithecus Homo erectus 0 1 2 3 4 5 7 6 Millions of years ago Homo sapiens 8 Chimps Gorillas Knuckle-walking Sahelanthropus Orrorin ? ? ? bipedalism Ardipithecus
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See over tall grass? Carry things? Wading? Why be a biped?
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Cost of Transport ( ml O 2 /kg/m) Chimps=0.20 Humans=0.05 Save energy! Sockol et al., 2007 Stand when feeding
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Stride = full cycle from heel strike (HS) to heel strike HS FF………. HO TO SWING…… BASIC TERMINOLOGY
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8% 43% 62% 100% STANCE PHASE SWING PHASE In a walk, the foot is on the ground for more than 50% of the time HS FF HO TO WALKING
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The inverted pendulum model PE KE
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0 10 20 30 40 50 60 70 80 90 100 0 50 100 150 Ground Reaction Force (% body mass) % stride cycle HS TO Single support Double support Double support 0 10 20 30 40 50 60 70 80 90 100 % stride cycle Potential energy Kinetic energy Energy
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Biomechanical challenge: move Center of Gravity (COG) forward economically and with stability COG: 2 cm anterior to 2nd sacral vert. 5 cm Oscillations of COG during walking = distorted figure of 8 4.5 cm
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DETERMINANTS OF GAIT* FUNCTION: minimize oscillations of COG vertical displacements (5) lateral displacements (3) anterior-posterior displacements (2) 4.5 cm 5 cm *Saunders et al., 1953 not today (take HEB 1420) }
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Determinant #1: Medial rotation Stance side hip rotates ! 4° medially (towards midline) about a vertical axis Increases stride length Effectively elongates leading and trailing legs at heelstrike, thus decreasing nadir of COG at heelstrike ! 1 cm
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This note was uploaded on 03/29/2012 for the course LS 2 taught by Professor Andrewa.biewener,petert.ellison,anddaniele.lieberman during the Fall '10 term at Harvard.

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LS2.Lecture29.gaits - LS 2 Lecture 29: HUMAN GAITS...

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