The paper deals with modeling of human-like reaching movements using optimal control theory. Typically, in the construction of optimization models, capturing the invariant features of human movements, the main emphasis is placed on the form of the optimality criterion. However, the boundary conditions are also an important part of the optimization problem. Considering reaching movements in the manipulation of flexible objects, we first show that the conventional imposition of the boundary conditions does not always produce a good match to the experimental data featuring the acceleration jumps in highly dynamic tasks. To explain the acceleration jumps, we reformulate the problem, using the concept of natural boundary conditions, and show that it improves the prediction of the experimental data. Finally, it is suggested how not only the acceleration but all the boundary conditions can placed in a natural way.