Description
Study Rationale: Disequilibrium while standing increases an individual's risk of injury, especially in the elderly population. To maintain upright posture, the body's center of mass must be stabilized in a central, equilibrium location over the feet, which act as the base of support (BOS) during standing. Segmental postural impairments such as forward head position, thoracic and lumbar kyphosis, misalignment of the knees, and foot/ankle abnormalities are all implicated in the literature as disrupting this relationship, subsequently contributing to instability and increased fall risk. These findings are equivocal, however, and certain individuals are better able to compensate for these imbalances than others. This suggests that a global approach to assessing postural alignment, accounting for any compensatory joint position changes, may provide a more accurate way to distinguish alignment imbalances that may lead to falls. To objectively identify and rehabilitate instability in patients and clients, health practitioners such as Physical Therapists and Personal Trainers require quantitative measures to determine how far these individuals have migrated from equilibrium positions. Purposes and hypotheses: The present study suggests a method for calculating global posture offset measures, using computerized posture analysis software, from coronal and sagittal view photographs of individuals during quiet standing. It was expected that these measures would accurately predict deviations of the line of gravity (LOG) (i.e., the ground projection of the body's center of mass measured with a force plate) away from an equilibrium position within the BOS. It was also expected that postural alignment abnormalities and/or deviations of the LOG would decrease the size of an individual's stability limits during a multi-directional leaning task, the NeuroCom Balance Master's Limits of Stability (LOS) test. To assess how physical activity behaviors may have affected the posture and balance relationship, participants responded to items on the Behavioral Risk Factor Surveillance System (BRFSS) questionnaire regarding physical activity and leisure time behaviors. It was expected that individuals who failed to meet the American College of Sports Medicine's 2011 minimum physical activity recommendations, and/or spent greater amounts of time watching television, would have greater deviations from ideal postural alignment and lesser balance control than those who reported meeting these recommendations and watched less television. Major findings: Healthy, adult participants (N=98, age range 18-75 years) with greater global coronal and sagittal posture offsets had greater deviations of the LOG away from an equilibrium position. These global posture offset measures predicted the location of the LOG (as estimated by center of pressure (COP) position) within 0.57cm in the medial/lateral direction and 1.33cm in the anterior/posterior direction. The resulting regression equations successfully predicted COP positions in an additional cross validation sample (N=20) of healthy adults with similar demographics. Postural offsets and COP positions were not significantly related to maximum excursions on the LOS test; however, postural offsets were inversely correlated with directional control scores, and both postural offsets and COP positions were positively correlated with movement velocity on this test. Demographic variables and BRFSS responses to neuromotor physical activity participation and TV-watching time were able to explain 42.8% of the maximum excursions participants attained on the LOS test. No relationships between physical activity behaviors or television-watching time and postural alignment were discovered. Conclusions: Overall, the findings in the present study suggest that postural alignment deviations are capable of influencing the location of the LOG during quiet standing. Global posture offset measures, provided by computerized posture analysis software, may offer health practitioners an objective, reliable method for identifying disequilibrium in their patients and clients. While the LOG location during quiet standing was not directly related to the maximum excursions participants achieved on the LOS test, it was related to the movement strategies participants employed when leaning toward targets, indicating that postural alignment may indirectly influence one's stability limits. Finally, physical activity and sedentary behaviors were poor predictors of postural alignment and balance performance. It is possible that no direct relationship exists between these measures, or, that self-reported physical activity behaviors are not the best measure to use when investigating the relationships between postural alignment, balance control, and fitness level.
