Computational Model for Load Carriage Systems Optimization

Soldiers and recreational backpackers are often required to carry heavy loads on their body during military operations or hiking. Shoulder strain appears to be one of the limiting factors of load carriage, probably due to higher susceptibility to short-term injuries such as soft tissue damage and trapped nerves or obstruction of blood vessels. The aim of the current study was to develop a versatile model for various loads and strap materials and structures in order to better simulate real life loading scenarios and to help in optimizing load carriage systems design and guidelines.Open-MRI scans were used for reconstructing a 3D geometrical model of an unloaded shoulder and for measuring the soft tissue deformations caused by a 25 kg backpack; subsequently, a subject-specific finite element (FE) stress-strain analyses was developed. Loads were applied at the strap-shoulder contact surfaces of the model by pulling the strap towards the shoulder until the desired load was reached. Increasing the loads up to 35 kg resulted in further increase in strains of the underlying soft tissues: The maximal tensile strain in the brachial plexus for a 25 kg backpack was 12%, and while carrying 35 kg, the maximal tensile increased to 16%. The lateral aspects of the brachial plexus were found to be more vulnerable to a deformation-inflicted injury, because there is less protection there against the compressive loads applied during load carriage. The newly developed model successfully enabled predictions of soft tissue deformations in the brachial plexus for different backpack loads. In addition, it allows further development of new strap structures and materials for alleviating the strains applied on the shoulder soft tissues.