Effect of Load Carriage on Upper Limb Performance

Carrying heavy backpacks are often associated with shoulder discomfort or pain, loss of sensorimotor functions, and brachial plexus injuries that might hamper performance. On the basis of previous research, the cause of these symptoms could be tissue deformations of the brachial plexus and the subclavian artery caused by the shoulder straps. Purpose: This study aimed to evaluate the changes in the upper extremity hemodynamic and neural function and to assess how they are associated with brachial plexus tissue deformation during heavy load carriage. Methods: Ten young healthy adults carried for 45 min a backpack load (40% of their body weight) while standing freely, followed by 15 min of recovery (unloaded). Indexfinger microvascular flow and sensorimotor function were measured before and after carrying the load, and after recovery. The following sensorimotor functions were measured: light touch thresholds by the index finger and little finger, forearm thermal sensation thresholds, and gross motor function. In addition, marksmanship accuracy, as an indication for fine motor function, was tested. Results: Load carriage resulted in an average decrease of similar to 40% in microvascular flow and a significant decrement in light touch sensation (P < 0.05), but not in thermal sensation and gross motor functions. An increase in the light touch threshold was highly correlated with a reduced index-finger microvascular blood flow (r = 0.79, P = 0.007). These physiological effects were associated with a functional 34% decrement in the accuracy of target acquisition. Conclusion: Heavy load carriage resulted in impaired light touch sensitivity and fine motor function, which were associated with reduced finger microvascular blood flow.