The work presented in this thesis is concerned with the measurement of gait and posture parameters and their variation due to load weight, gender and load carriage duration when carrying military loads. In particular it examines the load carriage system as a whole rather than the backpack alone, which has been the concentration of previous biomechanical load carriage research.

There were two main aims to the thesis: (1) to develop a mobile 'in-field' pressure measurement system to assess pressure at Body-Load Carriage System (LCS) interfaces (shoulders and hips). (2) To evaluate and compare prototype LCS designs in-field and to provide human factor requirements for design improvement. To satisfy the aims of the thesis in-field trials were carried out in a realistic military context. The purposes of these trials were to: (1) compare the standard issue British military LCS against a prototype LCS design in terms of pressure and subjective comfort; (2) increase the understanding of the properties of the shoulder and hip interfaces; (3) assess the relationship between loading at the shoulder and hip; and (4) identify whether other ergonomic issues are also important to consider. By assessing these areas human factors requirements for design were then determined. An additional (minor) aim was to develop a new prototype LCS with a greater degree of compatibility between the components of a military LCS (backpack and webbing), incorporation of material advances, and with a greater consideration for fit and posture. Four main experimental trials were performed the first (n = 11) assessedth e affect of clothing layers at the body-LCS interface on transmitted pressure. Results showed that clothing layers even worn in multiple have no effect on pressure transmission. Thus, no relief from pressure exists for the user. This highlighted the importance of the materials in the shoulder and hip straps. The second trial (n = 10) was a laboratory based comparison of two backpacks, the first the standard issue British military pack, the second a new prototype. Results found significant difference in subjective comfort and also peak pressure at the shoulder interface. The prototype backpack being associated with reduced peak pressure and increased comfort. The third trial (n = 10) assessed whole LCSs (backpack + webbing) in field with civilian participants. The standard issue LCS was compared against a prototype LCS. No significant difference in pressure was identified between the two LCSs, although differences in subjective comfort ratings were still significant indicating a preference for the prototype LCS. The final trial (n = 30) was military in-field trial. Military personnel and loadings were utilised. Again no significant difference in pressure data was identified although differences in subjective ratings remained significant with the prototype LCS design being preferred. Research findings highlighted the continued need for subjective assessment. The relationship between pressure loading at the shoulder and hip interfaces, along with locations of peak pressure within each interface were found to be important factors affecting comfort. Increased pressure distribution at the interfaces via new materials and design was also associated with increased comfort. Other areas which appeared important were the effect of posture and other physical forces not measured (i.e. shear and friction). Human factors guidelines were created for finiher LCS designs and future research ideas were presented.

This thesis consisted of two main research themes: 1) The biomechanics of military load carriage, and 2) injuries and discomfort caused by load carriage. Although different in their methodological approaches, the two sections are linked and integral to each other. Harman et al (2000) suggest that the biomechanical analysis of military load carriage, and in particular the study of ground reaction forces (GRF), is relevant to the understanding and prevention oflower extremity injuries. The general aims of the biomechanical analysis of load carriage were to determine the effect that heavy load carriage, rifle carriage and load distribution has on GRF parameters. In addition to determining the mechanisms behind these potential changes, base-line data for British military load carriage systems (LCS) were also established. An important factor for the thesis was to consider the LCS as a single unit (where possible) and not its individual components, for example the backpack alone. The final biomechanical study involved a 3D, bi-Iateral gait analysis of load carriage; with this type of analysis being rare in the published literature. Results from the biomechanical studies showed that GRF parameters increased proportionally to applied load, even when heavy loads of up to 40 kg were carried. Also seen was an increase in mediolateral impulse and stance time with greater carried load. Another area which has received little or no attention in the literature is the effect of rifle carriage on gait. This thesis showed that rifle carriage changed basal gait patterns as observed in the GRF parameters. The most noteworthy results were an increase in impact peak and mediolateral impulse. The mechanism behind these changes is most likely to be a restriction of natural arm swing induced by rifle carriage. Distributing load more evenly around the body had limited effect on the GRF parameters measured. However, some important changes were observed. These were an increase in force minimum and a decrease in maximum braking force at the heaviest load. The latter effect has been strongly linked to an increase in the incidence of foot blisters within the literature. Finally, the gait analysis study showed significant increases in joint moments and torques with carried load. Also observed was a decrease in stride length and increase in percentage double support and stance. The main kinematic differences were a decrease in range of motion at the knee and pelvis rotation, and an increase in pelvis tilt as load is added. Four further studies were conducted in an effort to determine the discomfort and injury caused by load carriage. The first 3 studies collected sUbjective discomfort data via interviews, questionnaires and the use of comfort ratings. All of which were collected either during or after a prolonged period of load carriage by military personnel. Results gleaned from these studies showed that the upper limb is susceptible to short term discomfort following load carriage, whereas the lower limb is not. The lower limb may be at an increased risk of developing medium to long term injuries such as joint degradation and stress fractures. However, foot pain was rated as the most uncomfortable skeletal region of the body following a 1 hour field march with load, and blisters were experienced by around 60% of participants. Shoulder discomfort commences almost as soon as load is added and increases steadily with time. However, foot discomfort seems to increase more rapidly once the discomfort first materialises. This early development of shoulder or foot pain may be a risk factor for severe pain or non-completion of a period of prolonged load carriage. Finally, females experienced more discomfort in the hip joint and feet compared to males. (Continues...).