Project Summary First responder, military, and law enforcement personnel regularly carry backpack loads of up to 60% body weight. Use of the hands and fingers is often needed during or immediately after load carriage, but loads applied via backpack straps can constrict blood flow and compress the brachial plexus nerves of the upper limb. These factors can potentially lead to pain, injury and impaired use of the upper limbs. Understanding the acute effects of heavy load carriage on upper limb physiology will aid development of field-based functional measures to reduce the risk of injury and prevent long-term loss of hand function. Persons who regularly carry heavy backpack loads for occupational purposes report incidences of pack palsy, a disability causing lack of sensation and weakness in the hands. The proposed work aims to investigate relationships among physiological changes, manual functional deficits during pack carriage, and pack palsy. It is unclear how the magnitude and duration of backpack carriage affects acute changes in grip strength, pinch strength, manual dexterity and light touch sensory threshold. The overall hypothesis is that walking with backpack load will cause changes in upper limb blood flow, edema, and nerve conduction. Further, we expect these physiological changes will result in measurable differences in manual dexterity, strength, and light touch sensory threshold that will change with increasing load in the backpack and duration of time walking with load. To address the hypotheses, I will determine the relative acute changes in upper limb blood flow, edema and nerve conduction before and after walking with heavy backpack load. I will also identify quantitative changes in blood flow, grip strength, pinch strength and manual dexterity at load levels of 15% and 30% body weight as compared to a control condition. I will explore the effects of walking time with backpack load on upper limb blood flow and light touch sensory threshold of the fingers which may be affected by nerve compression from backpack straps. This much needed research will improve understanding of upper limb physiological and neuromuscular changes with backpack carriage. The innovative methodology will allow study of multiple upper limb physiological changes simultaneously. Increased understanding of backpack carriage could improve prevention of brachial plexus injury and therefore reduce incidences of weakness or loss of hand function. Application of this work could lead to early diagnosis of brachial plexus compression by means of functional measures. Results of this work may improve hand function, injury prevention, and treatment of the upper extremity for those who carry heavy backpacks in an occupational or recreational setting.