Relation between Forward Lean and Ground Reaction Forces during Carrying Heavier Loads on Level Ground

Abstract

Load carriage is one of the key elements in dismounted military operations and is generally mission specific. Soldiers need to carry increasingly heavier occupational loads that may alter their gait mechanics, commonly affecting lower back, shoulders and lower limbs. Such responses, on long run, may impact on force generation and force sustainment, thus increasing the risk of injury. The loads are mostly carried in ensembles like backpacks (BP, 10.7kg) on back, haversack (HS, 4.4kg) and web (Wb, 2.1 kg) on waist and rifle (4.2kg) in hand or on shoulder, making a total of about 21.4kg. At times, depending on the operational requirement, they need to carry extra load in the BP. Present study measured the forward lean and ground reaction force responses in soldiers while they carried extra loads in the same BP designed for lower load. Twelve healthy male Indian Infantry soldiers with mean (SD) age 31.6(3.6)yrs, height 179.4(11.0)cm and weight 71.1(7.01)kg, volunteered for the study. They walked on a 10m walkway at self selected comfortable speed, without load and with carrying 21.4kg (existing load carriage ensembles, ELCe), 28.4kg (7kg added in BP) and 35.4kg (14kg added in BP), respectively. Their gait data were collected using 6 Camera based 3D Motion Analysis System and a pair of Kistler force plates. Results showed that forward lean and vertical ground reaction forces significantly increased when data for ELCe was compared with heavier loads carried in same BP. It may be concluded that putting more loads in the existing BP increases stress on musculoskeletal system leading to increased injury risk potential.