Modeling mechanical strains and stresses in soft tissues of the shoulder during load carriage based on load-bearing open MRI

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 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.

Effects of an exoskeleton on muscle activity in tasks requiring arm elevation: Part I - Experiments in a controlled laboratory setting

BACKGROUND

Long-term work with elevated arms, or overhead work, is a risk factor for musculoskeletal complaints and disorders. Upper-limb exoskeletons are a promising tool for reducing occupational workload when working with hands above shoulder level.

OBJECTIVE

The purpose of this study was to assess the effects of upper-limb exoskeleton on muscular and physical strain and perceived exertion during dynamic work at four different shoulder joint angles. Further, we evaluated if there are any negative effects associated with the use of exoskeleton.

METHODS

A total of 15 student participants performed dynamic work in laboratory setting with and without an exoskeleton at four different shoulder angles: 60, 90, 120 and 150 degrees. Muscle electrical activity from 8 muscles of the upper body, perceived exertion, and heart rate were measured during the work task, and grip strength, muscle stiffness, tone, and elasticity from six muscles, m. deltoideus physiological cross-sectional area and muscle fiber pennation angle, and nerve conduction velocity were measured before and after the work task.

RESULTS

Based on the results, the use of exoskeleton significantly reduced the muscle activity of the upper limb, shoulder, and back muscles. The reduction was most significant when the arm elevation was 120°, and in m. deltoideus muscle activity. RPE was also positively affected indicating reduction in workload when using exoskeleton.

CONCLUSION

The results suggest that the use of upper limb exoskeleton has potential to reduce physical workload during overhead work and, consequently, reduce the risk for work-related musculoskeletal disorders.

Comparison of In-service Reduced vs. Full Torso Coverage Armor for Females

INTRODUCTION

Body armor and torso-borne equipment are critical to the survivability and operational effectiveness of a soldier. Historically, in-service designs have been predominantly designed for males or unisex, which may be disadvantageous for females who are shaped differently and, on average, smaller in stature and mass than their male counterparts. This study assesses the biomechanical and performance impact of two Canadian in-service armors and fighting load conditions on females.

MATERIALS AND METHODS

Four tasks (i.e., range of motion, treadmill march [×2], and a wall obstacle) were performed in a Baseline condition and two in-service torso-borne equipment conditions; the full torso coverage (FTC) condition has full upper torso soft armor with the fighting load carried in a separate vest, while the reduced coverage (RC) has a plate carrier with fighting load integrated into the armor carrier, bulk positioned higher, and less torso coverage. Both used identical combat loads and front and back armor plates. Trunk range of motion, march lower limb kinematics, march shoulder and hip skin pressures, perceived discomfort after the march, and time to traverse a wall obstacle were captured. Data were collected to assess the biomechanics and usability of the systems for eight females, representative of military recruits. Linear mixed-effects models were created, and analysis of variances (ANOVAs) were then performed on all the outcome measures (P < .05). Tukey's post-hoc procedures were performed when appropriate (P < .05).

RESULTS

There were significant differences between the RC and FTC for the sit and reach test (P < .001), lateral bend test (P < .001), and wall traverse time (P < .01). In all cases, the RC outperformed FTC. There were no differences between the two in-service conditions with respect to hip, knee, and ankle flexion/extension. The RC average skin pressure was higher than the FTC at the left and right shoulders by 103% and 79%, respectively, and peak skin pressure at the left shoulder by 75%. Both in-service conditions showed decrements in performance from Baseline for sit and reach (P < .001), lateral bend (P < .001), and peak hip and knee flexion (P < .01) with the FTC showing decreases in trunk rotation (P < .001) and wall traverse time (P < .01).

CONCLUSIONS

Improved outcomes for the RC can be attributed to design differences. The lower placement of bulk in FTC may act as a physical barrier during range of motion tasks and the wall obstacle. The presence of shoulder caps on FTC provides another physical barrier that likely impedes full movement through the arms and shoulders. While the narrower shoulder straps of the RC remove the barrier, it causes more concentrated skin pressures on the shoulder that can lead to injury. The results suggest that the RC offers a potential for increased operational effectiveness in females (and potentially for males) compared to the FTC system. Shoulder pressure, an important predictor of discomfort and injury, is the only measure for which FTC outperformed the RC. Future torso-borne equipment designs targeting this outcome measure could help increase the effectiveness of the RC and other similar systems that reduce torso coverage, though survivability implications must also be considered.

Upper limb manual dexterity, strength and blood flow after walking with backpack load

This study aimed to characterize the effects of walking with backpack load on upper limb function. Fifteen males participated in 3 conditions: no load, 40% body weight loaded backpack (BP) and loaded backpack with simulated rifle (BRC). Pinch strength, grip strength, sensory threshold, blood flow volume, and a manual dexterity test were assessed before and after a 45-min walking trial. Pinch strength in the BP condition was significantly different than the control (p < 0.05). Grooved pegboard times were faster after a seated recovery (p = 0.026) than immediately after walking with load. Blood flow was significantly decreased to <53% of baseline (p ≤ 0.001) in BP and BRC immediately after donning the backpack. No significant changes in grip strength or sensory threshold were measured among conditions or time points. In conclusion, pinch strength, manual dexterity and blood flow were affected by backpack carriage, but other upper limb measures remained unaffected.

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.

Critical biomechanical and clinical insights concerning tissue protection when positioning patients in the operating room: A scoping review

An optimal position of the patient during operation may require a compromise between the best position for surgical access and the position a patient and his or her tissues can tolerate without sustaining injury. This scoping review analysed the existing, contemporary evidence regarding surgical positioning-related tissue damage risks, from both biomechanical and clinical perspectives, focusing on the challenges in preventing tissue damage in the constraining operating room environment, which does not allow repositioning and limits the use of dynamic or thick and soft support surfaces. Deep and multidisciplinary aetiological understanding is required for effective prevention of intraoperatively acquired tissue damage, primarily including pressure ulcers (injuries) and neural injuries. Lack of such understanding typically leads to misconceptions and increased risk to patients. This article therefore provides a comprehensive aetiological description concerning the types of potential tissue damage, vulnerable anatomical locations, the risk factors specific to the operative setting (eg, the effects of anaesthetics and instruments), the complex interactions between the tissue damage risk and the pathophysiology of the surgery itself (eg, the inflammatory response to the surgical incisions), risk assessments for surgical patients and their limitations, and available (including emerging) technologies for positioning. The present multidisciplinary and integrated approach, which holistically joins the bioengineering and clinical perspectives, is unique to this work and has not been taken before. Close collaboration between bioengineers and clinicians, such as demonstrated here, is required to revisit the design of operating tables, support surfaces for surgery, surgical instruments for patient stabilisation, and for surgical access. Each type of equipment and its combined use should be evaluated and improved where needed with regard to the two major threats to tissue health in the operative setting: pressure ulcers and neural damage.

Effect of external breast prosthesis mass on bra strap loading and discomfort in women with a unilateral mastectomy

BACKGROUND

A common complaint of women who wear external breast prostheses following mastectomy is that they are too heavy. This study aimed to investigate the effect of external breast prosthesis mass on bra strap loading, discomfort and perceived pressure in women with a unilateral mastectomy.

METHODS

Pressures exerted at the bra strap-shoulder interface and ratings of discomfort and perceived pressure (visual analogue scales; 0-12 cm) were recorded for 17 women (mean 68 (SD 5.7) years) who had a unilateral mastectomy. Data were collected during standing and walking while the women wore a Lightweight prosthesis and Standard-weight prosthesis. Pressure, discomfort and perceived pressure between the two prosthesis conditions were compared using Wilcoxon Signed Ranks and the sum of the pressure values during walking and standing were correlated with discomfort and perceived pressure scores using Spearman's Rho tests.

FINDINGS

Mean peak bra strap pressures were significantly less when the participants wore the Lightweight prosthesis compared to the Control prosthesis during walking (0.28 (SD 0.14) N/cm² versus 0.35 (SD 0.20) N/cm²; P < 0.05) but not during standing. No significant main effect of prosthesis mass on the participants' ratings of discomfort or perceived pressure were found, which were highly variable.

INTERPRETATION

Reducing external breast prosthesis mass decreased mean peak bra strap pressures during walking but this was not accompanied with reductions in bra strap-shoulder discomfort or perceived pressure. Treatment strategies to decrease bra strap-shoulder interface loading due to external breast prostheses mass could assist women who complain of prosthesis heaviness during physical activity.

The Interplay of Mechanical Stress, Strain, and Stiffness at the Keloid Periphery Correlates with Increased Caveolin-1/ROCK Signaling and Scar Progression

BACKGROUND

Fibroproliferative disorders result in excessive scar formation, are associated with high morbidity, and cost billions of dollars every year. Of these, keloid disease presents a particularly challenging clinical problem because the cutaneous scars progress beyond the original site of injury. Altered mechanotransduction has been implicated in keloid development, but the mechanisms governing scar progression into the surrounding tissue remain unknown. The role of mechanotransduction in keloids is further complicated by the differential mechanical properties of keloids and the surrounding skin.

METHODS

The authors used human mechanical testing, finite element modeling, and immunohistologic analyses of human specimens to clarify the complex interplay of mechanical stress, strain, and stiffness in keloid scar progression.

RESULTS

Changes in human position (i.e., standing, sitting, and supine) are correlated to dynamic changes in local stress/strain distribution, particularly in regions with a predilection for keloids. Keloids are composed of stiff tissue, which displays a fibrotic phenotype with relatively low proliferation. In contrast, the soft skin surrounding keloids is exposed to high mechanical strain that correlates with increased expression of the caveolin-1/rho signaling via rho kinase mechanotransduction pathway and elevated inflammation and proliferation, which may lead to keloid progression.

CONCLUSIONS

The authors conclude that changes in human position are strongly correlated with mechanical loading of the predilection sites, which leads to increased mechanical strain in the peripheral tissue surrounding keloids. Furthermore, increased mechanical strain in the peripheral tissue, which is the site of keloid progression, was correlated with aberrant expression of caveolin-1/ROCK signaling pathway. These findings suggest a novel mechanism for keloid progression.

Unbiased pattern analysis reveals highly diverse responses of cytoskeletal systems to cyclic straining

In mammalian cells, actin, microtubules, and various types of cytoplasmic intermediate filaments respond to external stretching. Here, we investigated the underlying processes in endothelial cells plated on soft substrates from silicone elastomer. After cyclic stretch (0.13 Hz, 14% strain amplitude) for periods ranging from 5 min to 8 h, cells were fixed and double-stained for microtubules and either actin or vimentin. Cell images were analyzed by a two-step routine. In the first step, micrographs were segmented for potential fibrous structures. In the second step, the resulting binary masks were auto- or cross-correlated. Autocorrelation of segmented images provided a sensitive and objective measure of orientational and translational order of the different cytoskeletal systems. Aligning of correlograms from individual cells removed the influence of only partial alignment between cells and enabled determination of intrinsic cytoskeletal order. We found that cyclic stretching affected the actin cytoskeleton most, microtubules less, and vimentin mostly only via reorientation of the whole cell. Pharmacological disruption of microtubules had barely any influence on actin ordering. The similarity, i.e., cross-correlation, between vimentin and microtubules was much higher than the one between actin and microtubules. Moreover, prolonged cyclic stretching slightly decoupled the cytoskeletal systems as it reduced the cross-correlations in both cases. Finally, actin and microtubules were more correlated at peripheral regions of cells whereas vimentin and microtubules correlated more in central regions.

Height adjustments on backpack-carrying systems and muscle activity

The aim of this study is to investigate the neuromuscular response of shoulder muscles at different attachment heights of a carrying system during arm movement. It was hypothesized that (1) different height adjustments lead to changes in muscle activity and (2) the shoulder horizontal provides a benchmark for the optimal attachment height of the shoulder belts. The musculus deltoideus was significantly relieved after the elevation of the shoulder belt for subjects with an initial attachment height of 2 cm below the shoulder. The musculus trapezius was relieved with the elevation above the shoulder. At a height of more than 2 cm above the shoulder, no further muscle unloading was achieved. These findings prove that a height adjustment can provide a systematic unloading or deloading of the shoulder musculature. Despite the fact that the magnitude and direction of changes in muscle activity lead to rather individual responses, the intra-individual responses are consistent. Therefore, support systems should provide the range of individual requirements.

Effects of an improved biomechanical backpack strap design on load transfer to the shoulder soft tissues

The aim of the present study was to characterize shoulder strap structure and mechanical properties that may alleviate strains and stresses in the soft tissues of the shoulder. Utilizing a finite element model of the shoulder constructed from a single subject, we have quantified skin stresses exerted by backpack straps and the strains at the subclavian artery (SCA). For this end, standard shape straps with stiffness of 0.5, 1.2, and 5 MPa, were compared to the effects of optimized straps; a double-layered (soft outer layer and reinforced internal supporting layer) and newly-designed anatomically-shaped strap. Compared to the standard 0.5 MPa strap, the 5 MPa strap resulted in 4-times lower SCA strains and 2-times lower Trapezius stresses. The double-layered strap resulted in 40% and 50% reduction in SCA strains and skin stresses, respectively, with respect to the softer strap. The newly-designed anatomical strap exerted 4-times lower SCA strains and 50% lower skin stresses compared to the standard strap. This demonstrates a substantial improvement to the load carriage ergonomics when using a composite anatomical strap.

The effect of shoulder strap width and load placement on shoulder-backpack interface pressure

BACKGROUND

Pressure on the shoulder can be a major limiting factor to backpack use and poor design can lead to pain and injury.

OBJECTIVE

To evaluate the effect of shoulder strap width and load placement in a backpack on the shoulder and axilla.

METHODS

A manikin fitted with a backpack load of 20 kg mass and four different width straps (5, 6, 7, and 8 cm) was used. The load was placed high or low. Interface pressure sensors were placed over the shoulder and chest wall at the axilla.

RESULTS

A significant interaction was observed between shoulder strap width and load placement. The positive effect of wide straps on shoulder pressure is greater with high load placement and the benefit of wide straps on axillary pressure is improved with low load placement. Interface pressure decreased significantly from narrow to wide straps. A large difference was noted between interface pressure on high and low load placement with narrow straps; however, as shoulder strap width increased, the difference between the two load placements decreased.

CONCLUSION

The least amount of interface pressure was observed with 8 cm shoulder straps and high load placement. These findings should influence design and use of backpacks.

Wheeled assistive device for load carriage - the effects on human gait and biomechanics

Soldiers are often required to carry loads which impose biomechanical strain on the human body. This can adversely affect physical performances. Recently, wheel-based devices (WBD) were designed to reduce the load on the soldier. In the present study, a prototype of this newly developed WBD was evaluated. Thirteen volunteers performed three exercise protocols on a treadmill as follows: (1) no load; (2) carrying 40% of their bodyweight with a backpack or; (3) with the WBD. Data acquisition included: gait parameters, vertical ground reaction forces (VGRF) and contact pressure acting on the shoulder. Biomechanical analysis showed that the WBD decreased the contact pressure on the shoulder and the VGRF. However, greater gait variability, in terms of cycle-to-cycle gait line generation, was observed, which might point to a difficulty in maintaining stability while walking. The study suggests that WBD has a potential to reduce the biomechanical strain on the soldier while carrying heavy loads. Future potential adjustments for the development of a better WBD-based solution are suggested. Practitioner Summary: The present research observed the potential biomechanical advantages of using a wheel-based device designed to reduce the load on the soldier. It contributed to a lower mechanical force on the soldier's body, yet causing modulations in gait control. Future design adjustments should be made to optimise the platform.

Validation of an instrumented dummy to assess mechanical aspects of discomfort during load carriage

Due to the increasing load in backpacks and other load carriage systems over the last decades, load carriage system designs have to be adapted accordingly to minimize discomfort and to reduce the risk of injury. As subject studies are labor-intensive and include further challenges such as intra-subject and inter-subject variability, we aimed to validate an instrumented dummy as an objective laboratory tool to assess the mechanical aspects of discomfort. The validation of the instrumented dummy was conducted by comparison with a recent subject study. The mechanical parameters that characterize the static and dynamic interaction between backpack and body during different backpack settings were compared. The second aim was to investigate whether high predictive power (coefficient of determination R²>0.5) in assessing the discomfort of load carriage systems could be reached using the instrumented dummy. Measurements were conducted under static conditions, simulating upright standing, and dynamic conditions, simulating level walking. Twelve different configurations of a typical load carriage system, a commercially available backpack with a hip belt, were assessed. The mechanical parameters were measured in the shoulder and the hip region of the dummy and consisted of average pressure, peak pressure, strap force and relative motion between the system and the body. The twelve configurations consisted of three different weights (15kg, 20kg, and 25kg), combined with four different hip belt tensions (30N, 60N, 90N, and 120N). Through the significant (p<0.05) correlation of the mechanical parameters measured on the dummy with the corresponding values of the subject study, the dummy was validated for all static measurements and for dynamic measurements in the hip region to accurately simulate the interaction between the human body and the load carriage system. Multiple linear regressions with the mechanical parameters measured on the dummy as independent variables and the corresponding subjective discomfort scores from the subject study as the dependent variable revealed a high predictive power of the instrumented dummy. The dummy can explain 75% or more of the variance in discomfort using average pressures as predictors and even 79% or more of the variance in discomfort using strap forces as predictors. Use of the dummy enables objective, fast, and iterative assessments of load carriage systems and therefore reduces the need for labor-intensive subject studies in order to decrease the mechanical aspects of discomfort during load carriage.

Load carriage, human performance, and employment standards

The focus of this review is on the physiological considerations necessary for developing employment standards within occupations that have a heavy reliance on load carriage. Employees within military, fire fighting, law enforcement, and search and rescue occupations regularly work with heavy loads. For example, soldiers often carry loads >50 kg, whilst structural firefighters wear 20–25 kg of protective clothing and equipment, in addition to carrying external loads. It has long been known that heavy loads modify gait, mobility, metabolic rate, and efficiency, while concurrently elevating the risk of muscle fatigue and injury. In addition, load carriage often occurs within environmentally stressful conditions, with protective ensembles adding to the thermal burden of the workplace. Indeed, physiological strain relates not just to the mass and dimensions of carried objects, but to how those loads are positioned on and around the body. Yet heavy loads must be borne by men and women of varying body size, and with the expectation that operational capability will not be impinged. This presents a recruitment conundrum. How do employers identify capable and injury-resistant individuals while simultaneously avoiding discriminatory selection practices? In this communication, the relevant metabolic, cardiopulmonary, and thermoregulatory consequences of loaded work are reviewed, along with concomitant impediments to physical endurance and mobility. Also emphasised is the importance of including occupation-specific clothing, protective equipment, and loads during work-performance testing. Finally, recommendations are presented for how to address these issues when evaluating readiness for duty.

Mechanical Predictors of Discomfort during Load Carriage

Discomfort during load carriage is a major issue for activities using backpacks (e.g. infantry maneuvers, children carrying school supplies, or outdoor sports). It is currently unclear which mechanical parameters are responsible for subjectively perceived discomfort. The aim of this study was to identify objectively measured mechanical predictors of discomfort during load carriage. We compared twelve different configurations of a typical load carriage system, a commercially available backpack with a hip belt. The pressure distribution under the hip belt and the shoulder strap, as well as the tensile force in the strap and the relative motion of the backpack were measured. Multiple linear regression analyses were conducted to investigate possible predictors of discomfort. The results demonstrate that static peak pressure, or alternatively, static strap force is a significant (p<0.001) predictor of discomfort during load carriage in the shoulder and hip region, accounting for 85% or more of the variation in discomfort. As an additional finding, we discovered that the regression coefficients of these predictors are significantly smaller for the hip than for the shoulder region. As static peak pressure is measured directly on the body, it is less dependent on the type of load carriage system than static strap force. Therefore, static peak pressure is well suited as a generally applicable, objective mechanical parameter for the optimization of load carriage system design. Alternatively, when limited to load carriage systems of the type backpack with hip belt, static strap force is the most valuable predictor of discomfort. The regionally differing regression coefficients of both predictors imply that the hip region is significantly more tolerant than the shoulder region. In order to minimize discomfort, users should be encouraged to shift load from the shoulders to the hip region wherever possible, at the same time likely decreasing the risk of low back pain or injury.

Shoulder skin and muscle hemodynamics during backpack carriage

The purpose of this study was to quantify the effects of loaded backpacks on shoulder muscle oxygenation, skin blood flow, and pain. We hypothesized that backpack load carriage is associated with lower shoulder muscle oxygenation and skin microvascular flow. Near-infrared spectroscopy quantified shoulder tissue oxygenation and laser Doppler flow measured skin microvascular flow. Eight adult volunteers donned a standard backpack without added load, 5 kg load, and 10 kg load for 5 min while standing. An 8 min rest period before each backpack donning condition ensured that all measured parameters returned to baseline. Data were analyzed using a repeated measures ANOVA and significance set at p < 0.05. Donning a 10 kg backpack significantly reduced shoulder muscle oxygenation by 22 ± 23% as compared to the empty backpack control condition (p = 0.023). In addition, a 10 kg backpack load reduced skin microvascular flow by 82 ± 22%, as compared to the empty backpack control condition (p = 0.024). Perceived pain was significantly higher when wearing the 10 kg backpack (level 4 on a 10-maximal pain scale) as compared to the empty backpack (0, 0-no pain) (p < 0.05). In conclusion, backpack loads of 10 kg decrease shoulder muscle oxygenation and skin microvascular flow.

Deformations in the Shoulder Tissues During Load Carriage: A Computational Model

Shoulder soft tissue deformations seem to be one of the limiting factors of load carriage among soldiers and recreational backpackers that are required to carry heavy loads. Yet, there are no loading limits related to the forces borne by the shoulders, and the backpacks designs are not consistent with providing pressure relief from this sensitive anatomical region. The aim of this study was to develop a model that will enable to study the biomechanical loads that develop in the shoulder under heavy loads and to help in optimizing load carriage systems design. A 3-dimensional, anatomically accurate finite element model of a human shoulder was constructed based on MRI scans. The model was developed to calculate the effective stresses on the skin below the shoulder strap (superficial loads) and the effective strain in the brachial plexus region (inner tissue deformation) for loads of up to 35 kg. The model successfully predicted deformations in the soft tissue surrounding the brachial plexus when compared with deformations measured from load-bearing MRI scans. The model yielded a skin pressure mapping, which showed pressure hotspots in the clavicle region. Inner tissue deformations mapping, as assessed by brachial plexus envelop strains, were found to peak at 30% effective strain at the lateral aspect below the pectoralis muscle. The newly developed model successfully predicted soft tissue deformations in the shoulder related to backpacks. This model can be used to optimize load carriage systems for better distribution of pressure over the shoulders and lower inner tissue deformations.

Bra strap orientations and designs to minimise bra strap discomfort and pressure during sport and exercise in women with large breasts

Background

Bra straps are a primary source of discomfort during sport and exercise, particularly for women with large breasts. This study aimed to investigate the effects of altering bra strap orientation and design on bra strap comfort, pressure and breast support in women with large breasts. This is a descriptive laboratory study.

Methods

Bra strap discomfort (visual analogue scale, 0 to 10), pressure (custom-designed 10 mm² calibrated pressure sensor, 0.5 to 24 kPa range, 50 Hz, S2011, Novel GmbH, Munich, Germany, placed under the right bra strap at the crest of each participant’s shoulder), preference ranking and vertical breast displacement (VBD; Optotrak Certus® motion capture system, 200 Hz, Northern Digital, Ontario, Canada) data during dynamic treadmill running and static upright standing (pressure only) were collected for 23 active women with large breasts (D+ cup size) while they wore an encapsulation sports bra with six different bra strap conditions (two bra strap orientations: vertical and cross-back; three bra strap designs: standard width, wide and gel).

Results

Bra strap discomfort was significantly less (p ≤ 0.001) in the vertical compared to the cross-back strap orientation, which was the most preferred orientation despite no significant difference in strap pressure. The wide strap design had the lowest discomfort scores, significantly lower strap pressure compared to the standard width and gel strap designs (p < 0.001), and was equally the most preferred design with the gel straps. There was no significant difference in VBD among the six strap conditions.

Conclusions

Bra straps that are vertically orientated and wide (approximately 4.5 cm in width) are preferable for women with large breasts during sport and exercise to minimise bra strap pressure and discomfort. The addition of gel pads under bra straps may also decrease discomfort and prevent straps slipping off the shoulders, although this notion warrants further investigation.

Bone geometry on the contact stress in the shoulder for evaluation of pressure ulcers: finite element modeling and experimental validation

This research presents the finite element modeling (FEM) of human-specific computed tomography (CT) data to study the effect of bone prominences on contact stress in the shoulder for prevention of pressure ulcers. The 3D geometry of scapula, skin, and surrounding soft tissues in the shoulder was reconstructed based on the anonymous CT data of a human subject in a prone posture (without loading on the shoulder) for FEM analysis of the contact stress. FEM analysis results show that the maximum stress is located at the prominence of the scapula with sharp bone geometry. This demonstrates that stress concentration at the bone prominence is a significant factor to cause the high contact stress, which is a source for pressure ulcers. For experimental validation, a physical shoulder model manufactured by 3D printing of the bone geometry and the mold for molding of tissue-mimicking silicone was developed. Compression tests of the mattress foam and silicone were conducted to find the nonlinear stress-strain relations as inputs for FEM. Experiments of compressing the shoulder model against the foam were carried out. Three flexible force sensors were embedded inside the model to measure the contact forces and compared to the FEM predictions. Results show that the FEM predicted forces match well with the experimental measurements and demonstrate that FEM can accurately predict the stress distributions in the shoulder to study the effect of bone geometry on the inception of pressure ulcers.

Dynamic measurement of pennation angle of gastrocnemius muscles during contractions based on ultrasound imaging

Background

Muscle fascicle pennation angle (PA) is an important parameter related to musculoskeletal functions, and ultrasound imaging has been widely used for measuring PA, but manually and frame by frame in most cases. We have earlier reported an automatic method to estimate aponeurosis orientation based on Gabor transform and Revoting Hough Transform (RVHT).

Methods

In this paper, we proposed a method to estimate the overall orientation of muscle fascicles in a region of interest, in order to complete computing the orientation of the other side of the pennation angle, but the side found by RVHT. The measurements for orientations of both fascicles and aponeurosis were conducted in each frame of ultrasound images, and then the dynamic change of pennation angle during muscle contraction was obtained automatically. The method for fascicle orientation estimation was evaluated using synthetic images with different noise levels and later on 500 ultrasound images of human gastrocnemius muscles during isometric plantarflexion.

Results

The muscle fascicle orientations were also estimated manually by two operators. From the results it’s found that the proposed automatic method demonstrated a comparable performance to the manual method.

Conclusions

With the proposed methods, ultrasound measurement for muscle pennation angles can be more widely used for functional assessment of muscles.