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Fig. 3. Apparatus used to rigidly restrict human ankle motion and control rolling
characteristics of the foot. (A) Subjects wore a boot and arc apparatus
bilaterally, each consisting of a rigid walking boot modified to accept wooden
arc shapes of varying radius. (B) `Arc foot' shapes of varying arc radius
(defined as fraction of leg length) were rigidly attached with pyramidal
prosthesis adapters. Arcs ranged in radius 0.020.40 m in absolute
dimensions, and each subtended a sufficient range of angles to ensure
continuous rolling ground contact throughout the stance phase. Arcs had
matched mass of 1.1±0.1 kg, and boots had mass 0.85 or 1.05 kg,
depending on size.