Carrying a rifle with both hands affects upper body transverse plane kinematics and pelvis–trunk coordination

Abstract

The purpose of this study was to assess how carrying a rifle in both hands affects upper body motion and coordination during locomotion. In total, 11 male soldiers walked (1.34 m/s) and ran (2.46 m/s) with a weapon (M4 condition) and without a weapon (NW condition) while kinematic pelvis and trunk data were collected. Two-way ANOVA was used to compare segmental ranges of motion (ROM), pelvis–trunk coordination (continuous relative phase) and coordination variability between gait mode and weapon combinations. Carrying a weapon decreased sagittal plane trunk ROM at both speeds and increased trunk rotation during running. Mean (±SD) transverse plane coordination was more in-phase while carrying a weapon (M4 = 83°±31, NW = 60°±36, p = 0.027) and transverse plane coordination variability decreased (M4 = 23°±3.6, NW = 15°±4.4, p = 0.043). Coordination differences between M4 and NW were similar to differences reported in the literature between individuals with and without back pain. Long-term injury implications due to decreased coordination variability are discussed.

Statement of Relevance: Knowledge of the effects of rifle carriage on pelvis–trunk coordination may provide insight into short-term protective strategies and long-term injury mechanisms. These should be considered in occupations requiring individuals to carry torso loads in combination with holding an object in both hands that restricts arm swing.

Keywords:

• biomechanics
• coordination
• locomotion
• relative phase
• rifle carriage

Acknowledgements

The authors would like to thank Sarah Conant for her substantial contributions to data collection and processing. The authors also thank Megan Coyne, Karen Gregorczyk and Albert Adams for assistance with data collection. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Army or the Department of Defense. Approved for public release; distribution is unlimited.