Figure 3.

Overview of experimental methods used to produce known hand counts. (A): Screenshots of movie showing two of the desired hand postures that participants had to mimic during the hand-only exercises. (B) Apparatus used for movement emulation. For wrist flexion and extension, the wrist joint was emulated, and the acrylic piece represented the hand and index finger together. For finger flexion and extension, the metacarpo-phalangeal (MCP) joint of the index finger was emulated and the acrylic piece represented the index finger only. (C) Measurements used for defining the emulated hand sizes in centimeters. The Manumeter was aligned with the wrist crease baseline and the magnetic ring was placed touching the interdigital folds of the index and middle finger. Dimension #1 is from the wrist crease baseline to the intersection of the distal transverse palm crease with the ulnar edge of the palm. This is the best approximation to the center of rotation for the MCP joint of the index finger. Dimension #2 goes from wrist crease baseline (which closely aligns with the center of rotation of the wrist) and the interdigital folds of the index and middle finger.