Despite the well-recognized role of lifting in low back injuries, the literature on safer lifting techniques remains controversial.
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Compression force limits have been recommended for safer manual material handling (MMH) maneuvers based on the premise that excessive compression loads could cause injury. Search for a safer lifting technique has attracted considerable attention due to the high risk of injury and low back pain (LBP) associated with frequent lifting in industry. Musculoskeletal impairments occur frequently and have a substantial impact on the health and quality of life of the population as well as on the health care resources. Results, for the tasks considered, advocate squat lifting over stoop lifting as the technique of choice in reducing net moments, muscle forces and internal spinal loads (i.e., moment, compression and shear force). Moreover, posterior shift in the position of the external load in stoop lift reaching the same lever arm with respect to the S1 as that in squat lift did not influence the conclusion of this study on the merits of squat lifts over stoop ones. For the relatively slow lifting tasks performed in this study with the lowering and lifting phases each lasting ∼2 s, the effect of inertia and damping was not, in general, important. These were due to significantly larger thorax, lumbar and pelvis rotations in stoop lifts. Net moments, muscle forces at different levels, passive (muscle or ligamentous) forces and internal compression/shear forces were larger in stoop lifts than in squat ones. Results satisfied kinematics and dynamic equilibrium conditions at all levels and directions. A dynamic kinematics-driven approach was employed accounting for the spinal synergy by simultaneous consideration of passive structures and muscle forces under given posture and loads. The model accounted for nonlinear properties of the ligamentous spine, wrapping of thoracic extensor muscles to take curved paths in flexion and trunk dynamic characteristics (inertia and damping) while subject to measured kinematics and gravity/external loads. Measurements were performed on healthy subjects to collect segmental rotations during lifts needed as input data in subsequent model studies.
In vivo kinematics measurements and model studies are combined to estimate trunk muscle forces and internal spinal loads under dynamic squat and stoop lifts with and without load in hands. The applicability of this method depends significantly on the type of firearm, ammunition, human factors, environment and other factors.Despite the well-recognized role of lifting in back injuries, the relative biomechanical merits of squat versus stoop lifting remain controversial. With a blind set of 6 cartridge cases, the errors were shown to average 122 cm from the known firing position. It was found that with an increasing number of cartridge cases used for shooter position estimation, the errors and standard deviation decreased, improving estimation results.
The blind testing sets ranged between 1 and 6 ejected cartridge cases with a known direction of fire.
The proposed method used the statistical data from the reference sample set and was tested on blind data sets to determine the errors and precision using “unknown” shooters. A reference sample set of more than 312 cartridge cases was collected from various people firing the same gun and ammunition from a known position and at different heights using a double-handed grip. Understanding the errors associated with shooter position estimation may give investigators a standardized method for establishing a reference set of cartridge cases which reflect the behavior of ejection patterns under controlled variables, while having a more reliable method when estimating a shooter’s position. This research is significant as there are no blind studies that determine the precision or errors when estimating a shooter’s position based on cartridge case ejection patterns. The purpose of this study is to propose a method to approximate a shooter’s position based on a reference sample set of cartridge case ejection patterns. Ejected cartridge cases in shooting incidents are useful in crime scene reconstruction to approximate the location of a shooter and the dynamics of an encounter.