The Nature of Movement Symmetry: Implications for Function and Injury Risk

Human movement requires an equipoise of mobility, strength, and neuromuscular control for optimal performance and injury protection. When certain movement asymmetries are present they create functional impairments that can negatively impact an individual’s performance and increase the likelihood for injury. This results in decreased quality of life due to missed time from work, sport, or social interaction and increased financial burden. There is limited evidence addressing what degree of asymmetry impacts functional performance or increases injury risk. Some activities such as throwing are naturally asymmetrical, thus asymmetry of the upper extremity may be beneficial in specific occupations or sporting professions. However, literature regarding asymmetries impact on injury risk in these populations is currently lacking. In sports such as basketball or soccer literature suggests that asymmetry may decrease performance and increase risk for injury. Current literature frequently cites an asymmetry of 10% or more as the predictor of increased injury risk. The purpose of this literature review is to identify movement asymmetries that warrant physical therapy intervention in an effort to improve functional performance and minimize injury risk. Movement asymmetries during functional activities can present in various ways, including range of motion, neuromuscular control or force production differences between limbs or within muscle groups. A review of the literature was completed to identify the implications for various movement asymmetries. Excluded were studies of leg length discrepancies, structural spinal conditions, or neurological conditions, as well as studies that included prepubescent children. Emerging literature trends suggest lower extremity symmetry is important for function and reducing injury risk. Movement asymmetries are most significant for tasks that demand bilateral weightbearing or for identifying readiness for return to sport. Asymmetry in the upper extremity has less of an impact on function or injury risk and appears to be acceptable when a task requires asymmetrical patterns or the demand remains within tissue tolerance