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THE UNIVERSITY OF CALGARY Eric Snively A ... - Ohio University

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This quantity approximates the vertical ground-reaction force acting upon the foot<br />

during fast linear locomotion, when the metatarsus is perpendicular to the ground<br />

(Figure 4.1).<br />

With the metatarsus at 90 degrees to the substrate, most of the ground-<br />

reaction force would be channeled vertically through the proximal phalanges and<br />

metatarsals. The proportion of FG channeled through a given metatarsal is<br />

directly proportional to the area of ground undemeath the element.<br />

To detemine relative areas, the metatarsus of TMP 94.1 2.602 was inverted,<br />

and the distal surface of each metatarsal was photographed from above. A<br />

plumb bob, hanging from the camera to the visual center of each distal surface,<br />

ensured that the three elements were photographed from the same distance. The<br />

photographs were scanned, and the relative areas determined by Object-Image<br />

for Macintosh software, from the United States Nationai Institutes of Health.<br />

Metatarsal III accounted for 0.4 of the total area; MT II and MT IV accounted<br />

for 0.3 each. These quantities and FG from equation 7 were substituted into the<br />

following equation:<br />

(8) FGMTX= (FG) (MTx%),<br />

where x is the number of the metatarsal and MTxOlb is me relative area. Figure<br />

4.1 diagrams the resulting axial forces on each metatarsal:<br />

FGmi=(37873 N)(0.3)=11362 N<br />

Fcmi~(37873 N)(0.4)=15149 N<br />

F~~nv=(37873 N)(0.3)=11362 N.

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