Fig. 2.
Graphical representation of the calculation of shoulder torques and the method used to evaluate the constancy of torque direction. A, The left andcenter plots show 1.5 sec of force (Fx, Fy) and torque (Tx, Ty,Tz) traces recorded at the transducer during the stimulation of MD at a single arm posture. Data from five consecutive trials aligned at stimulation onset are shown. These traces were averaged and combined using Equation 4 (see Materials and Methods) to obtain the traces on the right, representing the components of torque at the shoulder (Mx, My,Mz) in an arm-fixed frame of reference. Force units are Newtons (N), and torque units are Newton-meters (N-m). B, A three-dimensional torque trace obtained from AD during the ramp period of stimulation. The SD of the torque direction during this period had to be within the bounds of the 10° cone depicted here to be included in subsequent analyses.