1. A system for estimating motion parameters corresponding to a user, the system comprising: a Global Position System (GPS) receiver operable to receive GPS signals; an inertial sensor operable for coupling with the user and including one or more linear accelerometers arbitrarily oriented relative to the direction of user motion for generation of a signal corresponding to user motion; and a processing system in communication with the GPS receiver and inertial sensor, the processing system operable to— at least once, utilize the GPS receiver signals to estimate a first user speed parameter, utilize the inertial sensor signal to estimate a first user cadence parameter, at least once, generate a user-specific speed-to-cadence motion model to correlate user speed to user cadence using at least the estimated user speed and user cadence parameters, utilize the inertial sensor signal to estimate a second user cadence parameter, and at least once, utilize the motion model and the second user cadence parameter to estimate a second user speed parameter independent of the GPS receiver signals, wherein the second user speed parameter is estimated by the processing system by referencing the motion model without utilizing the GPS receiver signals such that the second user speed parameter may be estimated by the processing system when GPS signals cannot be received by the GPS receiver.