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382 P. A. WILLEMS, G. A. CAVAGNA AND N. C. HEGLUND

JEB9434 fig1

Walk Run

Upper arm

Lower arm

Thigh

Shank

Foot

Centre of mass

20J

100J

Upper arm

Lower arm

Thigh

Shank

Centre of mass

Mechanicale

nergy

0 20 40 60 80 100 0 20 40 60 80 100

Time (% of stride period)

Foot

Fig. 1

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