The effect of shoulder strap width and load placement on shoulder-backpack interface pressure.

Abstract

Pressure on the shoulder can be a major limiting factor to backpack use and poor design can lead to pain and injury. To evaluate the effect of shoulder strap width and load placement in a backpack on the shoulder and axilla. A manikin fitted with a backpack load of 20 kg mass and four different width straps (5, 6, 7, and 8 cm) was used. The load was placed high or low. Interface pressure sensors were placed over the shoulder and chest wall at the axilla. A significant interaction was observed between shoulder strap width and load placement. The positive effect of wide straps on shoulder pressure is greater with high load placement and the benefit of wide straps on axillary pressure is improved with low load placement. Interface pressure decreased significantly from narrow to wide straps. A large difference was noted between interface pressure on high and low load placement with narrow straps; however, as shoulder strap width increased, the difference between the two load placements decreased. The least amount of interface pressure was observed with 8 cm shoulder straps and high load placement. These findings should influence design and use of backpacks.