Abstract
Investigating the effects of load carriage on military soldiers using optical motion capture is challenging. However, inertial measurement units (IMUs) provide a promising alternative. Our purpose was to compare optical motion capture with an Xsens IMU system in terms of movement reconstruction using principal component analysis (PCA) using correlation coefficients and joint kinematics using root mean squared error (RMSE). Eighteen civilians performed military-type movements while their motion was recorded using both optical and IMU-based systems. Tasks included walking, running, and transitioning between running, kneeling, and prone positions. PCA was applied to both the optical and virtual IMU markers, and the correlations between the principal component (PC) scores were assessed. Full-body joint angles were calculated and compared using RMSE between optical markers, IMU data, and virtual markers generated from IMU data with and without coordinate system alignment. There was good agreement in movement reconstruction using PCA; the average correlation coefficient was 0.81 ± 0.14. RMSE values between the optical markers and IMU data for flexion-extension were less than 9°, and 15° for the lower and upper limbs, respectively, across all tasks. The underlying biomechanical model and associated coordinate systems appear to influence RMSE values the most. The IMU system appears appropriate for capturing and reconstructing full-body motion variability for military-based movements.
Highlights
Load carriage is an important component of typical occupational activities for military soldiers.When in the battlefield and during training, soldiers wear bulky clothing, stiff armour, and carry heavy backpacks
To better understand the demands placed on the body by typical military loads, researchers have studied the effects of load carriage on joint kinematics using optical motion capture
Between 4 and 9 principal component (PC) were retained for each movement to explain >90% of the variance for a total of 48 PCs across all movement types
Summary
Load carriage is an important component of typical occupational activities for military soldiers.When in the battlefield and during training, soldiers wear bulky clothing, stiff armour, and carry heavy backpacks. The items a soldier carries are lifesaving and operationally-relevant. They may lead to musculoskeletal injuries over time [1,2,3] and impair overall performance (e.g., movement speed and exposure time) [4,5]. To better understand the demands placed on the body by typical military loads, researchers have studied the effects of load carriage on joint kinematics using optical motion capture. Operationally-relevant loads increase trunk flexion, lower limb flexion range of motion (ROM), and walking speed during gait [6,7]. Optical motion capture requires line of sight between the cameras and body-mounted markers, which makes it challenging to study the effects of wearing military equipment as the markers must not be covered
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