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. 2009 Apr 22;4(4):e5176. doi: 10.1371/journal.pone.0005176

Figure 3. Schematic explanation of the setup and the three simulated tasks.

Figure 3

Representation of the simulated arm and its two antagonist muscles. F1: force developed by muscle 1. F2: force developed by muscle 2. R: radius of the sprocket. Black arrow: gravitational torque (GT) exerted on the segment. First row: Session I. Initial position (green circle) at 0°; Required movements: upward (red arrow), downward (blue arrow). Traces to the right: gravitational torque over time as a function of target movement amplitude and direction (upward: red, downward: blue). For all movements of session I, the gravitational torque varies monotonically and is independent of movement direction. Second row: Session II. Initial positions at 20° and −20°. The gravitational torque varies monotonically but depends on movement direction. Third row: Session III. Initial positions at 20° and −20°. For each movement (amplitudes: 40° and 60°) the gravitational torque varies non-monotonically.