The graphs also illustrate how angular velocity, the rate of change in joint angle, reflects the instantaneous slope of the displacement curve. Likewise, angular acceleration, the rate of change in angular velocity, represents the instantaneous slope of the velocity curve.
The graphs illustrate data published in Winter, D.A. (1987). The biomechanics and motor control of human gait. (1st ed.). Waterloo, Ontario: University of Waterloo.
Text version of a SAS program that produced the graphs.