Technical report | Load Carriage Capacity of the Dismounted Combatant- A Commander's Guide

Abstract

There is a universal requirement for military personnel to carry an external load. The load of military personnel is typically comprised of clothing, protective ensemble (i.e. body armour, helmet), combat equipment (i.e. webbing, weapon systems, ammunition, power sources, radio) and sustainment stores (i.e. food and water). In addition, military operations often requires dismounted personnel to move, on foot, through various climates and terrains for long and continuous periods. The total load varies dependant upon factors such as mission requirements and threat profile. Recent evidence suggests that the individual's load is increasing with advancing technologies and personal protective equipment. Excessive external load may adversely impact upon an individual's physical capability (e.g. mobility, lethality) and health (e.g. survivability, thermal burden). It is therefore important we consider (likely) individual load carriage capacity in mission planning. An individual's load carriage capacity is influenced by a multitude of factors that can broadly be categorised into three groups; 1) personnel characteristics (e.g. fitness, body mass, gender, age, injury profile, load carriage experience), 2) task characteristics (e.g. total external load, distribution of load, load carriage equipment design, movement speed, march duration, work to rest ratio) and 3) environment (e.g. terrain, heat, humidity, altitude) in which the task is performed. Some of these factors may in some situations be controlled (e.g. marching speed) whilst others are not (e.g. ambient temperature). There is a dynamic interaction between these factors which ultimately impact on an individual's load carriage capacity. When undertaking mission planning it is important for commanders to consider the factors influencing load carriage capacity and identify the likely burden.

Such information will guide amongst other things, duration of operations, work to rest schedules, total load limits, replenishment and logistical support requirements. This planning is critical to the maintenance of dismounted personnel's operational effectiveness, battlefield performance and ultimately mission success. This document reviews existing scientific literature and established work physiology models for the development of evidence-based load carriage guidelines. These guidelines will place emphasis upon critical task elements and human factors with the intent of assisting commanders' in making decisions about tasks involving load carriage. It is important to understand however that load carriage guidelines are not definitive nor can they be generically applied to all load carriage scenarios, rather they establish general principles to assist the commander in mission planning. Furthermore setting maximum absolute load limits or maximum intensity limits may be difficult to implement in the field and may not always be operationally possible. It is understood that mission requirements, operational constraints and threat profile dictate load carriage requirements. However mission planning needs to balance, to some degree, the requirements of the operational environment against the various physical considerations of personnel load carriage ability. Therefore, mission planners and commanders alike need to understand the impact of various load carriage variables on an individual's load carriage capacity and operational effectiveness.

Executive Summary

There is a universal requirement for military personnel to be capable of moving their body mass plus an external load. The load carried by military personnel is typically comprised of clothing, protective ensemble (i.e. body armour, helmet), combat equipment (i.e. webbing, weapon systems, ammunition, power sources, radio) and sustainment stores (i.e. food and water). In addition, the diversity and complexity of military operations often requires dismounted personnel to carry mission-specific equipment and move, on foot, through various climates and terrains for long and continuous periods.

The total load varies dependent upon factors such as mission requirements and threat profile. While the equipment carried is often crucial for mission success and survival, there are numerous examples through history demonstrating the adverse effect of heavy load carriage on soldier performance and operational success. Recent evidence suggests that the individual's load is increasing with advancing technologies and personal protective equipment. During current operations in Afghanistan anecdotal reports suggest that 50 kg is a common load carried by dismounted personnel whilst patrolling. Excessive external load may adversely impact upon an individual's physical capability (e.g. mobility, lethality) and health (e.g. survivability, thermal burden). It is therefore important we learn the lessons of the past and duly consider load carriage in mission planning involving dismounted personnel.

An individual's load carriage capacity is influenced by a multitude of factors that can broadly be categorised into three groups; 1) personnel characteristics (e.g. fitness, body mass, gender, age, injury profile, load carriage experience), 2) task characteristics (e.g. total external load, distribution of load, load carriage equipment design, movement speed, march duration, work to rest ratio) and 3) environment (e.g. terrain, heat, humidity, altitude) in which the task is performed. Some of these factors may in some situations be controlled (e.g. marching speed) whilst others are not (e.g. ambient temperature). There is a dynamic interaction between these factors which ultimately impact on an individual's load carriage capacity. When undertaking mission planning it is important for commanders to consider the factors influencing load carriage capacity and identify the likely burden. Such information will guide amongst other things, duration of operations, work to rest schedules, total load limits, replenishment and logistical support requirements. This planning is critical to the maintenance of dismounted personnel's operational effectiveness, battlefield performance and ultimately mission success.

The purpose of this document is to review existing scientific literature and established work physiology models for the development of evidence-based load carriage guidelines. These guidelines will place emphasis upon critical task elements and human factors with the intent of assisting commanders' in making decisions about tasks involving load carriage. It is important to understand however that load carriage guidelines are not definitive nor can they be generically applied to all load carriage scenarios, rather they establish general principles to assist the commander in mission planning.

An established predictive model has been used throughout this document to predict the physiological burden (i.e. energy cost) of representative load carriage scenarios. As a general guide this model indicates that a 10 kg increase in external load is metabolically equivalent (i.e. energy cost) to an increase in walking speed of 0.5 km/hr or a change in terrain gradient from level to 1%. An additional model provides commanders with guidance as to how long a continuous load carriage task can likely be sustained. As an example, it predicts that an average soldier can carry 40 kg at 5.5 km/hr over hard flat terrain for approximately 14 km. If that external load is increased to 50 kg the distance decreases to 9 km. If the walking speed is increased to 6.5 km/hr (from 5.5 km/hr) the likely distance the task can be sustained for decreases to approximately 6 km. This guidance highlights that total external load may at times be over-emphasised, to the detriment of other important factors e.g. walking speed. Commanders and mission planners therefore need to consider (at the very least) walking speed in conjunction with total external load given the potential for walking speed to illicit larger increases in energy cost for a load carriage task.

The multi-factorial nature of human load carriage capacity makes it difficult to set maximum load limits. Furthermore setting external load and/or intensity limits may be difficult to implement in the field and may not always be operationally possible. It is understood that mission requirements, operational constraints and threat profile dictate load carriage requirements. However mission planning needs to balance, to some degree, the requirements of the operational environment against the various physical considerations of personnel load carriage ability. Therefore, mission planners and commanders alike need to understand the impact of various load carriage variables on an individual's load carriage capacity and operational effectiveness.

This report has been divided into two parts; Part A discusses in detail the scientific aspects of load carriage while Part B provides a brief summary of scientific findings and guidance to commanders for tasks requiring load carriage. Within Part A, Section 2 outlines the methods applied to assess the physiological demand of load carriage. Sections 3 to 6 outline the physiological and biomechanical considerations of load carriage, the potential adverse health outcomes and the impact on tactical performance of the dismounted combatant. Within Part B, Section 7 provides a brief summary of science relating to military load carriage and highlights key areas of consideration for the commander. Section 8 identifies strategies to mitigate the impact of load carriage. Section 9 brings together all key physiological considerations to assist commanders in a) understanding the burden of load carriage, and b) planning a load carriage task. This information has been packaged in a table (Table 6), which provides commanders with an appreciation for the ability of individuals to (continuously) sustain a given load carriage task, under various operationally relevant parameters. It is important to understand that continuous work sustainment time does not consider other factors such as muscle discomfort and muscle fatigue, load carriage equipment integration and load carriage conditioning. These factors are known to reduce load carriage capacity before physiological factors (e.g. energy depletion), under certain conditions.

Finally, this guide is then distilled into an overview of key considerations for the management (i.e. preparation, execution and recovery) of personnel undertaking repeated load carriage tasks.