1. A method comprising, by one or more computing devices: accessing a first athletic-performance model of a first user, wherein: the first athletic-performance model is generated based on a first plurality of sets of action-parameter values of a plurality of action parameters and on a first plurality of outcomes of the first user, each of the first plurality of sets of action-parameter values being associated with a respective outcome of the first plurality of outcomes, the first plurality of sets of action-parameter values are determined based on biomechanical data of the first user performing a first plurality of actions of a first action-type, the first plurality of outcomes correspond respectively to the first plurality of actions, and the biomechanical data of the first user is received from one or more sensors comprising a first sensor, the first sensor being positioned on the first user to detect the biomechanical data of the first user while the first user is performing the first plurality of actions of the first action-type; determining a current skill level of the first user based on the first athletic-performance model of the first user, wherein the current skill level is determined based on a measure of one or more variances associated with one or more action parameters of the plurality of action parameters; computing one or more target ranges of action-parameter values for one or more selected action parameters of the plurality of action parameters based on the first athletic-performance model, wherein each target range is computed for the first user based on an analysis of the first plurality of sets of action-parameter values and of the respective first plurality of outcomes of the first user; and generating a report of athletic-performance feedback, the report comprising information related to the current skill level of the first user and the one or more target ranges of action-parameter values.