Integrating a hip belt with body armour reduces the magnitude and changes the location of shoulder pressure and perceived discomfort in soldiers

Walking Slope and Heavy Backpacks Affect Peak and Impulsive Lumbar Joint Contact Forces

Heavy load carriage is associated with musculoskeletal overuse injury, particularly in the lumbar spine. In addition, steep walking slopes and heavy backpacks separately require adaptation of torso kinematics, but the combined effect of sloped walking and heavy backpack loads on lumbar joint contact forces is unclear. Backpacks with hip belt attachments can reduce pressure under the shoulder straps; however, it is unknown if wearing a hip belt reduces lumbar spine forces. We used a musculoskeletal modeling and simulation approach to quantify peak and impulsive L1L2 and L4L5 lumbar joint contact forces in the anterior/posterior shear and compressive directions during walking on 0 deg and ±10 deg slopes, with no backpack and with 40% body weight backpack load using two different backpack configurations (hip belt assisted and shoulder-borne). Both walking slope and backpack load significantly affected shear and compressive peak and impulsive forces. The largest peak shear and compressive forces of 1.57 and 5.23 body weights, respectively, exceed recommended limits and were observed during uphill walking with shoulder-borne loads. However, only impulsive force results revealed differences due to the backpack configuration, and this effect depended on walking slope. During downhill walking only, the hip belt-assisted configuration resulted compressive impulses lower than during shoulder borne by 0.25 body weight seconds for both L1L2 and L4L5. These results indicate that walking uphill with heavy loads causes high shear and compressive lumbar forces that may increase overuse injury risk. In addition, our results suggest it is especially important to wear a hip belt when walking downhill.

The effects of shoulder morphology on the distribution of shoulder pressure during load carriage

To enhance the prevention of shoulder pressure injuries in various load-bearing populations, the effects of shoulder morphology on pressure distribution were investigated. In this study, 69 participants underwent three-dimensional scanning, and based on shoulder morphological characteristic indicators, they were classified into four shoulder types. From these, 28 participants were selected to have the pressure within shoulder regions measured using a pressure-sensing vest while carrying a backpack load equivalent to 15% of their body weight. The results indicated that variations in shoulder morphology significantly impact pressure distribution. The greater bumpiness of the shoulder surface contributed to pressure concentration at specific points, resulting in uneven pressure distribution. The enhanced fullness of the shoulder surface promoted even pressure dispersal across the area. This study provided a theoretical basis for developing more effective shoulder injury prevention and management strategies tailored to load-bearing populations with different shoulder types.

Electromyography and range-of-motion measurements in German soldiers wearing different types of body armour while marching

INTRODUCTION

In this study, we used surface electromyography (EMG) electrodes in order to measure and compare activity in the neck, back and thigh muscles of soldiers wearing two different types of body armour. A secondary objective was to analyse shoulder and hip ranges of motion using inertial motion sensors.

METHODS

Fourteen male soldiers were instructed to march 6 km on a treadmill while wearing different types of body armour. All participants wore shorts and a T-shirt and the same size vest regardless of their body size. We measured back and thigh muscle activity as well as shoulder and hip ranges of motion at regular intervals during the march.

RESULTS

Over the course of a 6 km march, muscle activity was already increased to 1.3 to 2.0 times after putting on the vest and increased by up to 13 times during the march with equipment. The new vest with hip belt required higher levels of muscle activity.

CONCLUSIONS

Body armour with hip belt placed higher levels of stress on back and neck muscles during a 6 km march than without. There was no major difference between the two types of body armour in terms of thigh muscle activity.

TRIAL REGISTRATION NUMBER

DRKS00016005.

Coupled effect of load weights and belt use on male shoulder pressure redistribution

Shoulder pressure redistribution is jointly affected by backpack loads and belt support. However, the combined effect of both factors has rarely been fully evaluated. Here, we studied the coupled effect of backpack loads and belt support on shoulder pressure redistribution. All twenty-eight healthy male subjects underwent eight loading conditions with both chest and hip belts fastened (CH) and unfastened (CON) in four conditions where the backpack weighed 7.5, 15, 22.5, and 30% of body weight (BW). Shoulder pressure distribution was quantified through a pressure-sensing vest mat. The results showed that using the hip belt and chest belt was effective in relieving the high pressure in the lateral clavicle and medial trapezius region and strengthening the load-bearing capacity of shoulder. However, the assistance in pressure relief of using belt was weakened when load increased to 30% BW. This study also showed that the belt use can be effective in improving pressure asymmetry on both sides.

The Effect of Body Armor on Pulmonary Function Using Plethysmography

Military tactical athletes face the unique task of performing physically demanding occupational duties, often while wearing body armor. Forced vital capacity and forced expiratory volume measured using spirometry have been shown to decrease, while wearing plate-carrier style body armor, little is known about the comprehensive effects of wearing body armor on pulmonary function, including lung capacities. Further, the effects of loaded body armor vs. unloaded on pulmonary function are also unknown. Therefore, this study examined how loaded and unloaded body armor affects pulmonary function. Twelve college-aged males performed spirometry and plethysmography under three conditions (basic athletic attire [CNTL], unloaded plate carrier [UNL], and loaded plate carrier [LOAD]). Compared to CNTL, LOAD and UNL conditions significantly reduced functional residual capacity by 14% and 17%, respectively. Compared with CNTL, LOAD condition also showed a small but statistically significant lowered forced vital capacity (P = .02, d = 0.3), a 6% lower total lung capacity (P < .01, d = 0.5), and lowered maximal voluntary ventilation (P = .04, d = 0.4). A loaded plate-carrier style body armor exerts a restrictive effect on total lung capacity, and both loaded and unloaded body armor affects functional residual capacity, which could impact breathing mechanics during exercise. Resulting endurance performance decreases may need to be factored based on the style and loading of body armor, especially for longer-duration operations.

Evaluating the intra- and inter-day reliability of output measures for the VALD HumanTrak: dynamic movements and range of motion of the shoulder and hip with body armour

The HumanTrak captures human movement through markerless motion tracking and can be a crucial tool in military physical screening. Reliability was examined in eighteen healthy participants who completed shoulder and hip ROM, and dynamic tasks in three body armour conditions. Generally, for all conditions, good to excellent reliability was observed in shoulder abduction and flexion, hip abduction and adduction, and dynamic squats knee and hip flexion (ICC ≥ 0.75 excluding outliers). Shoulder adduction and hip flexion demonstrated moderate to excellent reliability (ICC ≥ 0.50). Shoulder and hip extension and the drop jump were unreliable (ICC: 0.10-0.94, 0.15-0.89, and 0.30-0.82, respectively) due to the large distribution of ICC scores. Tasks with ROM values ≥ 100° involving movement towards or perpendicular to the HumanTrak camera tended to have greater reliability than movements moving away from the camera and out of the perpendicular plane regardless if body armour was worn.Practitioner summary: The HumanTrak analyses ROM in a time-efficient manner in a military setting. This study established that shoulder abduction and adduction (no body armour) and shoulder, hip, and knee flexion were the most reliable measurement for all conditions. Further work is required for movements across different planes.Abbreviations: ROM: range of motion; NBA: no body armour; BA: unloaded body armour; BA9: body armour with 9 kg; RGB: red, green, blue; ICC: intra-class correlation; SEM: standard error of measurement; MDC: minimal detectable change: MSE: mean square error; r: pearson correlations; N: sample size.

Does the fit of personal protective equipment affect functional performance? A systematic review across occupational domains

OBJECTIVE

To explore the effect of personal protective equipment (PPE) fit on functional performance across a range of occupational domains.

BACKGROUND

PPE introduces an ergonomic, human systems integration, and mass burden to the wearer, and these factors are thought to be amplified if PPE is ill-fitting. However, few studies have considered the role of fit (static, dynamic, and cognitive) when evaluating PPE-related performance detriments in occupational settings.

METHOD

A systematic literature review was conducted to identify relevant studies, which were then critically appraised based on methodological quality and collated to compare key findings and present evidence-based recommendations for future research directions across a range of occupational domains.

RESULTS

16 published studies met the inclusion criteria, 88% of which found that the fit of PPE had a statistically significant effect on occupational performance. Poorly sized PPE resulted in slower or increased reaction time; decreased range of motion or mobility; decreased endurance or tolerance; decreased pulmonary function; and altered muscle activation. Limited research met the inclusion criteria and those that did had risks of bias in methodology quality.

CONCLUSION

Future research evaluating the effect of PPE on performance in occupational settings should aim to recruit a more representative population; consider sex as a covariate; quantify and evaluate PPE fit and performance when integrated with all relevant equipment items; include outcome measures related to all three categories of fit (static, dynamic, cognitive); and assess performance of operationally relevant tasks.

Isolated Mononeuropathy From Rucksack Palsy: A Case Series

Although there is increasing awareness of brachial plexopathy secondary to rucksack use, isolated mononeuropathies have been less well described. Three cases of mononeuropathy secondary to rucksack use in military personnel are presented, including injuries to the long thoracic and spinal accessory nerves. We also review several different factors in the proper construction, components, and fitting of the rucksack that should be considered in order to prevent rucksack palsy and provide a concise suggestion for rucksack use and education.

Are female soldiers satisfied with the fit and function of body armour?

Design and development of contemporary military body armour has traditionally focused primarily on male soldiers. As the anthropometric body dimensions of male and female soldiers differ, we aimed to determine whether current body armour was meeting fit and functional requirements of female soldiers. One-hundred and forty-seven female Australian Defence Force soldiers completed a 59-item questionnaire regarding the fit and function of current body armour. Most (68%) participants reported wearing ill-fitting body armour, which was associated with increased total musculoskeletal pain and discomfort, as well as pain at the shoulders, abdomen, and hips. Body armour that was too large was more likely to interfere with task performance when it was integrated with a combat belt, as well as when female soldiers performed operationally representative tasks. Modifying body armour design and sizing to cater to the anthropometric dimensions of female soldiers is recommended.

Static, Dynamic, and Cognitive Fit of Exosystems for the Human Operator

OBJECTIVE

To define static, dynamic, and cognitive fit and their interactions as they pertain to exosystems and to document open research needs in using these fit characteristics to inform exosystem design.

BACKGROUND

Initial exosystem sizing and fit evaluations are currently based on scalar anthropometric dimensions and subjective assessments. As fit depends on ongoing interactions related to task setting and user, attempts to tailor equipment have limitations when optimizing for this limited fit definition.

METHOD

A targeted literature review was conducted to inform a conceptual framework defining three characteristics of exosystem fit: static, dynamic, and cognitive. Details are provided on the importance of differentiating fit characteristics for developing exosystems.

RESULTS

Static fit considers alignment between human and equipment and requires understanding anthropometric characteristics of target users and geometric equipment features. Dynamic fit assesses how the human and equipment move and interact with each other, with a focus on the relative alignment between the two systems. Cognitive fit considers the stages of human-information processing, including somatosensation, executive function, and motor selection. Human cognitive capabilities should remain available to process task- and stimulus-related information in the presence of an exosystem. Dynamic and cognitive fit are operationalized in a task-specific manner, while static fit can be considered for predefined postures.

CONCLUSION

A deeper understanding of how an exosystem fits an individual is needed to ensure good human-system performance. Development of methods for evaluating different fit characteristics is necessary.

APPLICATION

Methods are presented to inform exosystem evaluation across physical and cognitive characteristics.

The effects of a loaded rucksack and weighted vest on metabolic cost and stride frequency in female adults

This study evaluated the metabolic cost and stride frequency during exercise while wearing an evenly distributed weight vest in recreationally fit women. Nine healthy women performed a modified Balke treadmill test until volitional fatigue in one of three conditions; (1) unloaded (2) rucksack and (3) weighted vest. Wearing a weighted vest did not show improvement of V̇_O2peak, HR_peak, peak stride frequency or average stride frequency (all p ≥ 0.05). However, total time of exercise was significantly longer in the evenly distributed weight vest condition compared to the rucksack condition (p = 0.024) despite similar V̇_O2peak and HR_peak. These results may provide practical information when females in tactical populations are preparing for missions in which heavy loads must be carried. Practitioner summary: This study compared the effects of load carriage mode on metabolic cost and stride frequency during graded exercise in females. The weighted vest showed significantly longer exercise time despite similar V̇_O2peak and HR_peak. Development of standardised weight distribution mode may serve as an advantageous strategy for females in tactical settings. Abbreviations: HR: heart rate; V̇O2: oxygen uptake; RPE: rating of perceived exertion; V̇O2peak: peak oxygen uptake; HRpeak: peak heart rate.

Lower-limb joint work and power are modulated during load carriage based on load configuration and walking speed

Soldiers regularly transport loads weighing >20 kg at slow speeds for long durations. These tasks elicit high energetic costs through increased positive work generated by knee and ankle muscles, which may increase risk of muscular fatigue and decrease combat readiness. This study aimed to determine how modifying where load is borne changes lower-limb joint mechanical work production, and if load magnitude and/or walking speed also affect work production. Twenty Australian soldiers participated, donning a total of 12 body armor variations: six different body armor systems (one standard-issue, two commercially available [cARM1-2], and three prototypes [pARM1-3]), each worn with two different load magnitudes (15 and 30 kg). For each armor variation, participants completed treadmill walking at two speeds (1.51 and 1.83 m/s). Three-dimensional motion capture and force plate data were acquired and used to estimate joint angles and moments from inverse kinematics and dynamics, respectively. Subsequently, hip, knee, and ankle joint work and power were computed and compared between armor types and walking speeds. Positive joint work over the stance phase significantly increased with walking speed and carried load, accompanied by 2.3-2.6% shifts in total positive work production from the ankle to the hip (p < 0.05). Compared to using cARM1 with 15 kg carried load, carrying 30 kg resulted in significantly greater hip contribution to total lower-limb positive work, while knee and ankle work decreased. Substantial increases in hip joint contributions to total lower-limb positive work that occur with increases in walking speed and load magnitude highlight the importance of hip musculature to load carriage walking.