Many horses in training show motion asymmetries, but it is not known if these are due to pain caused by training; or due to individual biological variations. The aim of this project is to initiate three cohort studies where changes in motion symmetry will be monitored over time in riding horses and trotters. The prevalence and degree of motion asymmetry will be studied in young horses before and after training is initiated and in adult riding horses competing on advanced level. The project will give us important information on when asymmetries arise and how they develop over time. If horses have mild motion asymmetries that do not change over time, with different types of training, this could indicate natural persistent asymmetries. The proposed study is also highly useful for future studies where detailed information on training and management may lead to identification of risk factors for development of orthopedic lesions and improve interpretation of clinical use of motion symmetry.