Military load carriage: an innovative method of interface pressure measurement and evaluation of novel load carriage designs

This thesis is concerned with the measurement and effects of pressure on the body as a result of military load carriage. High skin pressures are associated with impaired blood flow, brachial plexus disorders and user pain and discomfort. Load carriage research has largely overlooked this issue, mainly due to the lack of an appropriate methodology. The thesis consists of two parts. The aim of part I was to develop and validate a novel method of measuring on-body interface pressures underneath military load carriage equipment. The Tekscan system was used, which provides 954 individual sensing elements over a total sensing area of 238.5cm2. A number of small experiments were undertaken to establish appropriate calibration and measurement error. A five-point rating scale was developed, and included within the experimental procedure; to measure user discomfort at the shoulder area where was 'no discomfort' and 5 was 'unbearably uncomfortable'. Following a pilot study the method was shown to produce reliable data that was sensitive to differences in design of load carriage systems within a comparative experimental design. [Continues.

The effect of weighted body armor on close combat reaction time and core muscle activation

The purpose of this study was to measure the choice reaction time and myoelectric activity of the right and left rectus abdominus, and right and left external obliques required to initiate movement in response to a visual stimulus that signaled performance of four different closecombat movements (left or right cross and left or right dodge). Reaction time and myoelectric activity were then compared with performing the movements in response to the visual stimulus while wearing a weighted vest that simulated wearing tactical body armor. Myoelectric activity was measured as the average root mean square (RMS) of the surface electromyography (sEMG) values. The hypotheses were that average time to react to the visual stimulus for each movement and average myoelectric activity to initiate the movement would be greater under the weighted vest condition. The participants were 10 active martial arts/boxing performers from different disciplines with a minimum one year experience in their discipline. During two separate sessions, the participants completed eight warm-up trials and 24 measured trials, with the first four trials deleted. The stimuli were activated in a random order with foreperiods ranging from 10 to 20 seconds between trials. The sessions were randomly chosen to be either loaded or unloaded conditions. Surface EMG electrodes detected the myoelectric activity of the right and left rectus abdominus, and right and left external oblique muscles. The electrodes pre-amplified the myoelectric signals by a factor of 35. The sEMG signals of the four muscles were treated with a 20 Hz low cut/high pass filter, amplified by a factor of 20,000, and the RMS of the filtered signals were derived using an 11.75 ms time window. The analog RMS sEMG was sampled at 1020 Hz and converted to digital form. The reaction time for each movement was determined from the initiation of the stimulus to the point at which myoelectric activity iv reached the threshold of 0.5 volts. A two-tailed paired samples t-test was run to determine differences between the average reaction time and average RMS sEMG for each core muscle during each movement for the unweighted and weighted conditions. A one-way ANOVA with repeated measures was run to determine significant differences in average reaction time and average total muscle activity between the unweighted and weighted conditions for the group. Alpha was set at 0.05. Significant differences were found between the unweighted and weighted conditions for reaction time while performing the left dodge, right cross, and right dodge with slight significance for the left cross (p = 0.047, p = 0.014, p = 0.002, and p = 0.059, respectively). Further, group average reaction time was significantly greater in the weighted condition (p = 0.001). No significant differences were found in initial muscle activity between the conditions. These results support the first hypothesis that mean reaction time would significantly increase when performing close-quarters combat movements in response to a visual stimulus while wearing a loaded vest. Combatives instructors, specifically military and law enforcement, can use this information as a means to further protect the armed forces by training them in the protective gear that they will be wearing out in the field. This will hopefully acclimatize the armed forces to a point where performance will not hinder to complete missions in hostile environments

Schoolbag Weight Carriage in Children: The Analysis of Ground Reaction Forces during Walking, Running and Jumping

Public society and international scientific community have shown concern about the heavy scholar backpacks carried by children. The possible adverse effects on children’s health of carrying those heavy loads have been in the base of that concern. Thus, the purpose of this thesis was to improve the understanding of school backpacks problem and to contribute to a solution. Specifically, it was our aims: (i) review the existing evidence concerning the characterization of backpack carrying, the known impacts and the solutions; (ii) characterize the loads that students in Portugal carry on their backpacks; (iii) understand how those loads influences the GRF acting on subjects and; (iv) propose modifications on backpack design that do not significantly modifies the main design but can attenuate the GRF magnitude increments. The main conclusions were: (i) scientific community still couldn’t clearly and consistently identified the effects of carrying backpack loads on children health. There are several body structures been studied as they could be affected. Also, there are not a consensus around the load limit that children should carry, however, the limit that seems to be more often recommend is the 10% of the body weight; (ii) the population analysed, students in Portugal, often carried more load than the recommended 10% of body weight. 5th grade students carry more absolute load than the 9th grade students; (iii) the load carried influenced the ground reaction forces. That influence was different in function of the mean of locomotion and the age/school grade, and (iv) with the backpack modification, the introduction of elastic material on the backpack straps, were verified changes on the influence of the backpack carrying in GRF, mainly the decrease of force peaks and loading rate. The main findings of this study confirmed the idea that children in Portugal may be carrying heavier loads on their backpacks than they should, especially the younger ones, and that it influences the ground reaction forces acting on them. However, we saw that is possible to introduce discrete modifications on typical backpacks than can attenuate that effect. It is needed to study, in the future, the way that benefits can be maximized and should not be forgiven the organization/pedagogical measures that may reduce the backpack load.A comunidade científica internacional e a sociedade em geral, têm manifestado preocupação relativamente às elevadas cargas transportadas pelos alunos diariamente para a escola. Os possíveis efeitos adversos do transporte dessas cargas na saúde das crianças têm estado na base da preocupação. Assim, o intuito deste trabalho foi melhorar o conhecimento acerca do problema das mochilas escolares e contribuir para uma solução. Especificamente, foram nossos objetivos: (i) rever as evidências existentes concernentes à caracterização do transporte das mochilas, os impactos conhecidos e as soluções propostas; (ii) caracterizar as cargas que os alunos em Portugal transportam; (iii) perceber como essas cargas influenciam as forças reativas do solo que atuam sobre as crianças, e (iv) propor e estudar modificações no design das mochilas que não o alterem significativamente mas que consigam atenuar o incremento da magnitude das forças reativas do solo. As principais conclusões foram: (i) a comunidade científica ainda não identificou de forma clara e consistente os efeitos do transporte das mochilas na saúde das crianças. São várias as estruturas do corpo que estão a ser estudadas como pudendo ser afetadas, mas os resultados não são consistentes. Também não existe consenso acerca do limite de carga que as crianças devem transportar, porém, o limite que mais é recomendado na literatura é 10% do peso corporal; (ii) a população analisada, alunos em Portugal, transportam frequentemente cargas superiores aos 10% recomendados. Os alunos mais novos, do 5º ano de escolaridade, transportam cargas absolutas superiores aos alunos do 9º ano; (iii) a carga transportada influenciou as forças reativas do solo. Essa influência variou em função do tipo de locomoção e do ano de escolaridade, e (iv) com a modificação proposta para a mochila, a introdução de material elástico nas alças, verificaram-se alterações na influência sobre as forças reativas do solo, principalmente a diminuição da magnitude dos valores de pico e da taxa de carga. Estas conclusões confirmaram a noção de que as crianças podem estar a transportar cargas demasiado elevadas para a escola, especialmente os mais novos, e que isso influencia as forças reativas do solo que atuam sobre eles. Contudo, vimos que é possível realizar alterações discretas nas mochilas escolares típicas, que podem atenuar esse efeito. Será necessário estudar a forma como essa vantagem poderá ser maximizada, sem esquecer as medidas organizacionais e pedagógicas que podem reduzir a carga a ser transportada

Laboratory investigation of a load carriage task observed in forestry

The objective of the present study was to investigate and compare the human responses to two load carriage tasks performed with three different load masses and on three different gradients. The task of carrying hydrogel in one hand was observed in a silviculture industry and crude physiological and perceptual responses were measured. This task was simulated in a laboratory setting together with a suggested intervention of backpack carriage. Eighteen conditions were established which consisted of the two modes of carriage and a combination of three load masses (9kg, 12kg and 15kg) and three gradients (5%, 10% and 15%). Twenty eight Rhodes University female students comprised the sample and the experimental procedures were conducted on a Quinton treadmill. Each participant was required to complete nine of the eighteen conditions which were each four minutes in duration. Postural changes were assessed using lateral and posterior digital images taken at the second and fourth minute and compression and shearing forces were estimated with the ErgolmagerTM Physiological responses (heart rate, ventilation and metabolic responses) were measured continuously with the Quark b² and perceptual responses ('central' and 'local' RPE) were measured every minute during the experimentation and body discomfort was rated at the completion of each condition. Overall responses revealed that hand carriage (146 bt.min⁻¹ , 25.09 mIO₂. kg-l.min⁻¹) was generally found to be more physiologically stressful than backpack carriage (130 bt.min⁻¹, 22.15 mIO₂.kg⁻¹ .min⁻¹) independent of load mass and gradient. Physiological responses were higher (113 bt.min-1 to 174 bt.min⁻¹ ) in responses to increasing gradient as opposed to increasing load mass (104 bt.min-1 to 153 bt.min⁻¹ ) for both backpack and hand carriage. Categorisation using the guidelines of Sanders and McCormick (1993) allowed for classification of conditions, with respect to physiological responses, into 'moderate', 'heavy' and 'very heavy' stress. For almost all of the physiological responses the majority of conditions which were classified as 'moderate' were backpack carriage conditions and the conditions classified as 'very heavy' were mostly hand carriage conditions. In terms of postural responses hand carriage resulted in more strain and greater compression and shearing forces on the spine. In terms of the compression forces increasing gradient had a greater affect on backpack carriage (681 N to 935 N) compared to hand carriage (570N to 793N). In contrast, increasing load mass had a larger affect on hand carriage postures and compression forces (751 N to 935N) in comparison to backpack carriage (723N to 780N). Shearing forces were found to be worse in hand carriage conditions overall. Although participants generally underrated perceived exertion in relation to cardiorespiratory responses, these perceptions revealed that backpack carriage, with a mean 'central' RPE of 12 compared to 11 for hand carriage, was somewhat preferred to hand carriage and that increasing gradient was perceived to be marginally more straining than increasing load mass

Barefoot vs. Shod: Effects of Trunk Loading and Body Mass Index on Walking Mechanics

In this dissertation, the impacts of increased mass and footwear on walking mechanics and energetics were investigated. In the first study, non-obese individuals were asked to walk on a treadmill with added load to the trunk (~15% of body mass) and with and without shoes. Metabolic costs of walking increased ~12% with added load, but walking barefoot did not significantly change metabolic costs. Trunk loading increased knee and hip range of motion but failed to alter spatiotemporal measures. In study 2, non-obese individuals were asked to complete the same tasks, but this time they walked overground instead of on a treadmill. The focus of this study was on lower extremity kinetics, which were not addressed in the first study. Loading increased stance and double support times, ground reaction forces, and joint moments and powers. Walking barefoot decreased spatiotemporal measures and ground reaction forces, but increased hip and knee moments and powers. Finally, in study three, rather than increasing body mass artificially by adding an external mass to the trunk, obese individuals with BMIs greater than 30 kg∙m-2, but less than 40 kg∙m-2, were recruited. Similar to Study 2, walking barefoot reduced stride length, stance time, and double support time. Barefoot walking also decreased vertical and anteroposterior ground reaction forces. However, joint moment and power responses to footwear conditions were dependent on body morphology, as the Obese and Non-Obese groups responded differently to these footwear conditions. Therefore, footwear condition should be reported and considered when comparing conclusions of multiple studies. Statistical outcomes for kinetic dependent measures also differed with normalization. Four joint kinetic measures (including ankle dorsiflexor and hip extensor moments, and knee and hip powers), were larger in the Non-Obese group than the Obese group after normalization, but did not differ when considered in absolute units. On the other hand, ten joint kinetic measures, including ankle, knee, and hip joint moments and powers, were larger in the Obese group in absolute terms. All ten of these were not different from the Non-Obese group after normalization. Varying normalization schemes partially explains differing outcomes reported in the literature regarding obesity’s impact on gait mechanics. Based on outcomes of the three studies presented here, ground reaction forces appear to scale with total weight, whether this is an external load (Study 2) or a consequence of obesity (Study 3). Walking barefoot decreased stride length, stance time, and double support time and ground reaction forces regardless of loading or obesity. However, joint kinetic responses to footwear appear to be dependent on body morphology, as the Obese and Non-Obese groups responded differently to these conditions

THE EFFECTS OF BODY ARMOR ON LOWER BACK AND KNEE BIOMECHANICS DURING BASIC AND MILITARY INSPIRED TASKS

With increased military personal protection equipment, body armor, comes the addition of carried load. Such person protection in recent history has been instrumental in combating the imminent threats (e.g., improvised explosive devices) of hostile environments, preventing otherwise lethal injuries. However, body armor has been suggested to degrade warfighters’ performance and compound the risk of musculoskeletal injuries. Both performance and risk of injury are intensely related to joint biomechanics. Therefore the objective of this project was set to determine the immediate and prolonged effects of wearing body armor on biomechanics of the lower back and knee. A randomized cross-over study design, wherein 12 sex-balanced, physically fit, young participants completed a series of tests before and after 45 min of treadmill walking with and without body armor. Tests included two simple tests (i.e., toe-touch and two-legged squat), two military inspired tests (i.e., box drop and prone to standing) and four knee torque tests (i.e., maximum isometric contraction of knee flexors and extensors, and concentric and eccentric isokinetic contraction of knee flexors and extensors. During these tests, kinematic, kinetic and torque measurements were used to investigate the immediate and prolonged effects of exposure to body armor on several measures of knee and lower back mechanics related to performance and risk of injuries. For the simple tests, the immediate effects of body armor were an increase of \u3e 40 ms (p ≤ 0.02) in flexion duration of the dominant joint and an ~1 s (p ≤ 0.02) increase in overall test duration as well as an ~18% (p = 0.03) increase in the lumbopelvic rhythm ratio near mid-range trunk flexion. For the military inspired tests, the immediate effects of body armor were an increase of ≥ 0.02 s (p ≤ 0.001) in temporal test durations and an increase of ~158 N (p = 0.01) box drop peak ground reaction force. Finally during the dynamometer testing, the BA condition was found to cause a greater reduction, ~10 N•m, in the maximum isometric strength of knee flexors (p = 0.04) and an increase (p ≤ 0.03) of strength ratios compared to the no armor condition

Examining the impact of protective clothing on range of movement

This chapter will address another of the possible contributors to the increased metabolic rate observed when wearing protective clothing. The nature of the protection required in industries where workers are exposed to extreme cold, heat and fire often means garments are constructed of thick, heavy, insulative material. The impact of these garments on ease of movement, range of motion and work efficiency has been referred to in the literature using various terms; clothing bulk, movement restriction and hobbling effect. But the effects have been hard to measure and quantify and so the possible involvement of clothing bulk in increasing energy cost in the wearer is still not clear