Plantar Pressure Responses to Backpack Load in Long-Distance Hikers: A Cross-Sectional Observational Study

Background: Long-distance hiking usually requires carrying a backpack, adding external load to the lower limbs and modifying plantar loading patterns. Excessive loads may contribute to overuse injuries, but quantitative evidence to support current recommendations on backpack weight is still scarce. This study aimed to examine how different backpack loads influence plantar pressure in long-distance hikers. Methods: A cross-sectional observational study was conducted in adults who had walked at least 20 km during the previous 24 h. Sociodemographic and clinical variables were recorded, and barefoot plantar pressure was assessed using the Podoprint® system under four conditions: without a backpack, with the habitual backpack, and with backpacks loaded to 10% and 20% of body weight. Static and dynamic plantar pressure parameters were analyzed using repeated-measures comparisons. Results: A progressive increase in plantar force was observed in both feet as backpack load increased. Compared with the unloaded condition, static forefoot pressure rose by 5.41% with a 10% load and by 8.73% with a 20% load (p = 0.005); rearfoot pressure increased by 5.01% and 10.17% (p = 0.015); and total foot pressure by 5.04% and 9.61% (p = 0.002). Loads above 10% of body weight significantly modified static plantar pressures and were associated with measurable changes during dynamic assessment. Conclusions: In long-distance hikers, carrying a backpack that exceeds approximately 10% of body weight leads to a clear, load-dependent increase in plantar pressure. These findings provide biomechanical support for recommendations that advise limiting backpack load to around 10% of body weight to reduce plantar stress during hiking.