The book "Optimization-based dynamic human gait prediction" by Yujiang Xiang presents an innovative methodology for simulating human walking using a spatial digital human model. This model features 55 degrees of freedom, with muscle actions at a joint summarized by the torque at each degree of freedom. The work employs cubic B-spline interpolation for time discretization and the established Denavit-Hartenberg method for the kinematic analysis of the mechanical system. The equations of motion are developed through a recursive Lagrange formulation, while the ground reaction forces are determined using a novel two-stage active-passive algorithm. A standout feature of this methodology is that the equations of motion are not explicitly integrated but evaluated within the optimization process through inverse dynamics. In addition to normal walking, various scenarios are considered, such as walking with a shoulder backpack of different weights, walking at varying speeds, asymmetric step lengths, and reduced torque limits.