Backpacks are used by more than 90% of schoolchildren worldwide and over 40 million students in the United States on a regular basis. The carriage of loaded backpacks is associated with kinematic and physiological changes, as well as complaints of neck and back pain. Since a history of backpain in childhood is the strongest predictor of having musculoskeletal discomfort and back pain as an adult, development of back pain due to backpack use is of prognostic concern. The purpose of this dissertation was to examine the effects of backpack weights (up to 20% body weight (BW)) on children’s posture, subjective complaints of pain and perceived exertion, and walking endurance. A secondary goal was to examine the data to identify and recommend a weight limit for backpacks carried by elementary school children based on the results. In Chapter 2, we performed a preliminary study designed to examine the effects of loaded backpacks on forward head posture in school children. The results of this study found that forward head posture increased with both backpack weight and condition. The greatest differences were noted at the 15% and 20%BW backpack loads with initial loading, but after 6 minutes of walking the forward head posture was similar for all backpack loads. In Chapter 3, we conducted a study to evaluate multiple postural angles and the subjective complaints of pain and perceived exertion/fatigue in children to determine the effects of both the weight and time spent carrying loaded backpacks up to 20%BW. Subjects showed significant changes in all measures including the Six Minute Walk Test (6MWT), OMNI Walk/Run Scale of perceived exertion/fatigue and subjective complaints of pain, as well as the postural angles of Craniovertebral Angle, Forward Trunk Lean, and Pelvic Tilt. Subjects demonstrated immediate and significant changes in forward head posture, forward trunk lean, and pelvic tilt while wearing backpacks weighing 10%, 15% and 20%BW, but the 10%BW backpack resulted in the least amount of change. This study also found that these postural angles changed additionally after walking 6 minutes while carrying the loaded backpacks. Subjects also demonstrated decreased 6MWT distances and increased reports of perceived exertion and pain after carrying backpacks weighing 10%, 15% and 20%BW. In Chapter 4, we discussed the clinical implications of this research. It was determined that backpack loads weighing 10%, 15% and 20%BW of a child’s body weight result in immediate changes in posture, which continue to increase after walking six minutes with the loaded backpack. The backpack loads significantly impacted the children’s walking endurance as well as their reports of perceived exertion/fatigue and regional pain. This study found that of the loads tested, the 10%BW resulted in the least amount of change in all outcome measures. However, the 10%BW load was not innocuous, as it still created significant changes in posture and subjective complaints. Backpack weight limit guidelines need to be written to protect children from carrying backpacks weighing more than 10% body weight.