Effect of a load distribution system on mobility and performance during simulated and field hiking while under load

Abstract

This study was conducted to test a modular scalable vest–load distribution system (MSV-LDS) against the plate carrier system (PC) currently used by the United States Marine Corps. Ten Marines engaged in 1.6 km load carriage trials in seven experimental conditions in a laboratory study. Kinematic, kinetic, and spatiotemporal gait parameters, muscle activity (electromyography), heart rate, caloric expenditure, shooting reaction times, and subjective responses were recorded. There was lower mean trapezius recruitment for the PC compared with the MSV-LDS for all conditions, and muscle activity was similar to baseline for the MSV-LDS. Twenty-seven Marines carrying the highest load were evaluated in the field, which measured an increase in energy expenditure with MSV-LDS; however, back discomfort was reduced. The field evaluation showed significantly reduced estimated ground reaction force on flat-ground segments with the MSV-LDS, and the data suggest both systems were comparable with respect to mobility and energy cost.

Practitioner summary: This study found that a novel load distribution system appears to redistribute load for improved comfort as well as reduce estimated ground reaction force when engaged in hiking activities. Further, hiking with a load distribution system enables more neutral walking posture. Implications of load differences in loads carried are examined.

Abbreviations: AGRF: anterior-posterior ground reaction forces; CAREN: Computer Assisted Rehabilitation Environment; GRF: ground reaction forces; HR: heart rate; ML-GRF: mediolateral ground reaction forces; MOLLE: Modular Lightweight Load-carrying Equipment; MSV-LDS: modular scalable vest–load distribution system; NHRC: Naval Health Research Center; PC: plate carrier; PPE: personal protective equipment; RPE: rating of perceived exertion; SAPI: small arms protective insert; sEMG: surface electromyography; USMC: United States Marine Corps; VGRF: Ground reaction forces in the vertical.

Keywords:

• Load carriage
• gait
• virtual environments
• back pain
• body armour

Acknowledgements

The authors wish to acknowledge the significant contributions of Joseph Hudak, MSG, U.S. Army; Andrew Jensen; Amanda Markham; Kathrine Haluch; Laura Arrington; LCDR Seth Reini, MSC, USN; Dr. Weimin Zheng; and Dr. Jennifer Neugebauer during this investigation.

Disclosure statement

I am an employee of the U.S. Government (KR Kelly). This work was prepared as part of my official duties. Title 17 U.S.C. § 105 provides the “Copyright protection under this title is not available for any work of the United States Government.” Title 17 U.S.C. § 101 defines a U.S. Government work as work prepared by a military service member or employee of the U.S. Government as part of that person’s official duties.

This data was supported by Program Manager Infantry Combat Equipment, Marine Corps Systems Command, under work unit no. N1310. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of the Army, Department of the Air Force, Department of Veterans Affairs, Department of Defense, or the U.S. Government. Approved for public release; distribution unlimited.

Human subjects participated in this study after giving their free and informed consent. This research has been conducted in compliance with all applicable federal regulations governing the protection of human subjects in research (Protocols NHRC.2013.0022 and NHRC.2014.0021). No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors wish to thank Product Manager Infantry Combat Equipment, U.S. Marine Corps Systems Command, for the financial support, as well as 1st Reconnaissance Battalion and 1st Marine Regiment, 1st Marine Division, for their assistance in subject recruitment.