The effect of simulated school load carriage configurations on shoulder strap tension forces and shoulder interface pressure

Determination of dynamic air gap thickness and analysis of its relationship with firefighters' joint movement

Objectives. The purpose of this study was to calculate the dynamic air gap thickness between the human body and the turnout gear. Relationships between the air gap thickness and joint range of motion (ROM) were also explored. Methods. The air gap thickness and joint ROM of 12 male firefighters walking in a control condition with no self-contained breathing apparatus (SCBA) and three varying-strapped SCBAs were measured using three-dimensional (3D) body scanning and 3D inertial motion capture. The interpolation technique was employed to predict the air gap thickness curve during walking. The dynamic air gap thickness was compared with the joint ROM to see how they relate to the location and percentage of movement restriction. Results. During the walking, the air gap fluctuated as a sine curve. Carrying SCBA reduced the air gap thickness at the trunk most (F = 11.17, p < 0.001, η2 = 0.63), and adjusting the shoulder strap length altered the air gap distribution at the trunk. The reduced air gap at the pelvis caused an incremental restriction on pelvis rotation. Conclusions. A compatibility design of the shoulder strap and hip belt in SCBA with the turnout jacket is suggested.

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.

Is skin pressure in load carriage over-evaluated?

Skin pressure is a biomechanical measure widely used in the assessment of load carriage systems. However, because of the complicated contour of human body, the stiffness of the pressure sensor array, and the large range of measurable pressures, there is much variability in previously reported results. In this paper, a simple mechanical model for load carriage was proposed, and the skin pressures beneath the shoulder and hip straps were predicted from the strap forces based on Laplace's law. The proposed model was used to analyze data from literature with an aim to check the reliability of existing pressure measurements. The static and dynamic pressures at five locations on eight subjects wearing a backpack with a 10 kg load, while standing and walking on a treadmill, were measured respectively using pressure sensors of the air pack type. The combination of literature data analysis and experimental testing proved that the existing measurement method of interface pressure in load carriage systems often leads to over-estimation and this might misguide the pressure criteria set for load carriage system usage and design. The proposed model will be useful for quick prediction of the interface pressure in load carriage systems.

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.

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.

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.

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.

Ergonomics evaluation of school bags in Tehran female primary school children

BACKGROUND

More than 90% of the elementary school students in the world and most of the Iranian students use backpacks. Heavy school bags, failure to apply ergonomics standards in student's backpacks, and also mismatch between anthropometrics dimensions and schoolbag size are important issues for children's health.

OBJECTIVE

The purpose of this study was to gather baseline information on the average weight carried by female primary students. It also aimed to evaluate ergonomics standards for student backpacks.

METHODS

A cross-sectional study was conducted on 212 Iranian girl students aged 6- 11 years. Body weight and bag weight were measured with electronic scales and body mass index calculated with WHO software 2007. A questionnaire was constructed to gather information about the backpacks. Body dimensions were measured with VICON motion Analyze system (460). Ergonomics factors were recorded using a checklist.

RESULTS

80.8% of the students used a backpack at a higher weight than recommended by the standards of 10% of body weight. The most common type of schoolbag used was double strap packs (92.5%). The majority of the students carried packs on their backs; however, most of them did not make any adjustments (79.8%). The results have shown a mismatch between the anthropometric measures and the student's backpack dimensions.

CONCLUSIONS

Parents, students and school staff should be informed about these critical issues as well as suitable controls should be implemented in buying and using the bags.

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.

Effect of backpack shoulder straps length on cervical posture and upper trapezius pressure pain threshold

[Purpose] This study was performed to investigate the effect of the length of backpack shoulder straps on upper trapezius muscle pain threshold and craniovertebral angle. [Subjects and Methods] There were 25 participants, with ages from 15 to 23 years old. Upper trapezius pain threshold and craniovertebral angle were measured for all subjects without the backpack then re-measured after walking on a treadmill for 15 min under 2 conditions: 1) wearing a backpack with short straps; and 2) wearing a backpack with long straps. [Results] there was a significant reduction in upper trapezius pain threshold and craniovertebral angle while carrying a backpack with long shoulder straps, compared to use of a backpack with short shoulder straps or no backpack. [Conclusion] A backpack with short straps is less harmful than a backpack with long straps. This result should be considered in ergonomic design of backpacks to reduce the incidence of various physiological and biomechanical disorders.

EPIDEMIOLOGY OF MUSCULOSKELETAL DISORDERS IN PRIMARY SCHOOL CHILDREN IN BOSNIA AND HERZEGOVINA

Introduction:

Musculoskeletal disorders represent a significant problem of modern society which are more pronounced in young people and school children. Etiology of these disorders is found in inadequate ergonomic conditions, too heavy school bag, school furniture inadequate to age, poor posture, sedentary lifestyle, reduction of physical activity and lack of exercise.

Material and methods:

This cross-sectional study included 1315 pupils aged 8- 12 years. As a method was used “cluster sample” in the selection of subjects. The survey was conducted by questionnaire containing information on the demographic and individual characteristics of participants (age, gender, class), the manner and style of life and the performance of school tasks, followed by standardized Nordic questionnaire. The following parameters were measured: body height and weight for each student, and the weight of full and empty school bag that students that day brought to class.

Results:

The incidence of musculoskeletal pain regardless of localization was 48%. There is a statistically significant correlation between acute pain in the right shoulder and total weight of school bags, duration of caring the bag in school and time of wearing bag from school to home but not with the manner in which school bag was carried. Acute pain in the right shoulder and acute neck pain were significantly associated with the duration of sitting in school or in front of a computer at home. Acute pain in the shoulder negatively correlated with BMI percentile value of the respondents. Acute pain in the neck is also significantly associated with the weight of a full school bags, as well as time spent sitting at home doing homework. Acute back pain is statistically significantly correlated with the weight of school bags and duration of sitting periods in school.

Conclusion:

The prevalence of musculoskeletal pain, particularly chronic pain in school children aged 8-12 years is high. Weight of school bags, manner in which the bag is carried to and from school, duration of carrying bags, time spent sitting in the school and in front of the computer, duration of sitting and posture during homework, body mass index are ergonomic reasons for the development of musculoskeletal pain.

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.

Schoolbag carriage and schoolbag-related musculoskeletal discomfort among primary school children

Schoolbag carriage is a common occurrence and has been associated with musculoskeletal discomfort in children. The current study investigated the relationship between schoolbag-related musculoskeletal discomfort and individual, physical and psychosocial risk factors in primary school children in Ireland. A cross-sectional survey and pretest-posttest quasi-experimental design was used. The site and intensity of musculoskeletal discomfort was assessed before and after schoolbag carriage to provide a dose-response assessment of schoolbag-related discomfort for the first time. Objective measurements of the children, schoolbags and other additional items were made, and a researcher assisted questionnaire was completed on arrival at school. A total of 529 children (male 55.8%: female 44.2%) with a mean age of 10.6 years ± 7.14 months were included. The majority had backpacks (93.8%) and 89.7% (n = 445) carried the backpack over 2 shoulders. The mean schoolbag weight (4.8 ± 1.47 kgs) represented a mean % body weight (%BW) of 12.6 ± 4.29%. Only 29.9% carried schoolbags that were ≤10%BW. A significantly greater proportion of normal weight children carried schoolbags that were >10%BW compared to overweight/obese children (p < 0.001). The mean %BW carried was 18.3 ± 5.03 for those who had an additional item. The majority (77.5%) carried schoolbags to school for ≤10 min. The prevalence of baseline musculoskeletal discomfort was high (63.4%). Schoolbag-related discomfort was reported more frequently in the shoulders (27.3%) than in the back (15%). The dose-response assessment indicated that both statistically and meaningfully significant increases in discomfort were observed following schoolbag carriage. Multiple logistic regression models indicated that psychosocial factors and a history of discomfort were predictors of schoolbag-related back discomfort, while gender (being female) and a history of discomfort were predictors of schoolbag-related shoulder discomfort. None of the physical factors (absolute/relative schoolbag weight, carrying an additional item, duration of carriage, method of travel to school) were associated with schoolbag-related discomfort. This study highlights the need to consider the multi-factorial nature of schoolbag-related discomfort in children, and also the need to identify background pain as its presence can inadvertently influence the reporting of 'schoolbag-related' discomfort if it is not accounted for.

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.

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.

Short-term effects of backpack carriage on plantar pressure and gait in schoolchildren

PURPOSE

To assess the effects of backpack carriage on plantar pressure distributions and spatio-temporal gait parameters among children.

PARTICIPANTS

Two hundred-eighteen schoolchildren, aged 6-13, and attending primary and secondary schools in the city of Cagliari (Italy).

METHODS

Participants were tested at school, during regular days. A pressure plate and wearable inertial sensors were used to measure plantar pressures and spatio-temporal parameters of gait. Measures were obtained during both quiet standing and walking, and both with and without a backpack. The latter contained those items a child had on the testing day.

RESULTS

Participants carried a mean mass in their backpacks of 5.2 kg, and more than half had a backpack/body mass ratio higher than 15%. While spatio-temporal gait parameters were not affected by backpack carriage, significant increases (up to 25%) in plantar pressures were found during both static standing and walking, especially in the forefoot.

CONCLUSION

Under realistic conditions, the impact of backpack carriage was more evident on foot-ground interaction than on gait features. However, long-term consequences of altered plantar pressure need to be assessed in future work, considering the actual durations typically spent carrying school items.

Neck, shoulder and low back pain in secondary schoolchildren in relation to schoolbag carriage: should the recommended weight limits be gender-specific?

The occurrence of neck, shoulder and low back complaints in relation to schoolbag carriage and other potential risk factors were investigated in a cross-sectional study of 586 Iranian schoolchildren aged 12-14 years. The average load carried by schoolchildren was 2.8 kg. Neck, shoulder and low back complaints during the preceding month were reported by 35.3%, 26.1% and 33% of the students, respectively. Gender was an independent factor predicting musculoskeletal symptoms in schoolchildren. Girls were more likely than boys to suffer from neck, shoulder and low back complaints, although there was no significant difference between genders in terms of schoolbag carriage variables. The findings suggest that the recommended weight limit for schoolbag carriage may need to differ between boys and girls. The associations between schoolbag variables and reported symptoms are also discussed. The results provide evidence that the current weight limit should consider a broader combination of factors that influence the use of schoolbags.

Association of Parental Awareness of Using Schoolbags With Musculoskeletal Symptoms and Carrying Habits of Schoolchildren

The association between parental awareness of using schoolbags and the occurrence of musculoskeletal symptoms and carrying habits of children was investigated in a cross-sectional study in Tabriz, Iran. Data on 454 students aged 11−14 years and their parents ( n = 358) were analyzed. The awareness of the recommended weight limit, appropriate method of carrying schoolbags, and schoolbag strap adjustments was generally low among the respondents. A higher parental awareness of the schoolbag weight was associated with a lower prevalence of upper back and shoulder complaints among children and carrying loads less than 10% of their body weight. The findings suggest that parental awareness should have a more prominent role in changing the schoolbag carrying habits of children and particularly in reducing the weight of loads carried by them. This highlights the need to incorporate guidelines and recommendations into practice to ensure that the health and safety of schoolchildren are not compromised when using schoolbags.

Effects of firefighters' self-contained breathing apparatus' weight and its harness design on the physiological and subjective responses

To examine the effects of firefighters' self-contained breathing apparatus' (SCBA) weight and its harness design on the physiological and subjective responses, eight male students performed treadmill exercise under four conditions: the 8 kg firefighter protective clothing (PC) (Control), the PC + an 11 kg SCBA with an old harness (Test A), the PC + a 6.4 kg SCBA with an old harness (Test B) and the PC + a 6.4 kg SCBA with a new harness (Test C), at ambient temperatures (T(a)) of 22°C and 32°C. Besides highlighting the fact that a heavy SCBA had a significant effect on the oxygen consumption and metabolic rate, this experiment also found that in a T(a) of 32°C, in particular, the combined effect of 4.7 kg lighter SCBA and new harness design could reduce metabolic rate and improved subjective muscle fatigue and thermal discomfort.

PRACTITIONER SUMMARY

An effort to alleviate the physiological and subjective burden of firefighters by reducing the weight of SCBA and by using the new harness design has provided satisfactory results in reduced oxygen consumption and in improved subjective responses in a hot air environment.

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

Shoulder strain is a major limiting factor associated with load carriage. Despite advances in backpack designs, there are still reports of shoulder discomfort, loss of sensorimotor functions, and brachial plexus syndrome. The current study is aimed at characterizing mechanical loading conditions (strains and stresses) that develop within the shoulder's soft tissues when carrying a backpack. Open MRI scans were used for reconstructing a three-dimensional geometrical model of an unloaded shoulder and for measuring the soft tissue deformations caused by a 25-kg backpack; subsequently, a subject-specific finite element (FE) model for nonlinear, large-deformation stress-strain analyses was developed. Skin pressure distributions under the backpack strap were used as reference data and for verifying the numerical solutions. The parameters of the model were adjusted to fit the calculated tissue deformations to those obtained by MRI. The MRI scans revealed significant compression of the soft tissues of the shoulder, with substantial deformations in the area of the subclavian muscle and the brachial plexus. The maximal pressure values exerted by a 25-kg load were substantial and reached ∼90 kPa. In the muscle surrounding the brachial plexus, the model predicted maximal compressive strain of 0.14 and maximal tensile strain of 0.13, which might be injurious for the underlying neural tissue. In conclusion, the FE model provided some insights regarding the potential mechanisms underlying brachial plexus injuries related to load carriage. The large tissue deformations and pressure hotspots that were observed are likely to result in tissue damage, which may hamper neural function if sustained for long time exposures.

THE EFFECT OF LOAD CARRIAGE AMONG PRIMARY SCHOOL BOYS: A PRELIMINARY STUDY

Backpack carrying is a considerable daily "occupational" load among schoolchildren. Most of the research on children's backpacks have focused on gait pattern and trunk forward lean; only a few researches have investigated the impact of backpack carrying on children using the measurements of static posture and gait kinetics. This study investigated the changes in ground reaction force (GRF) and trunk inclination among primary students when carrying heavy backpacks. A randomized controlled experimental study was conducted on seven boys aged between 9 and 11 years old with a similar body mass index. Observations were done when the boys were carrying school bags of 0% (as control), 10%, 15%, and 20% of their own body weight while walking normally. Data acquisition was carried out using force platforms and a 3D motion analysis system. A significant difference in GRF at a load of 20% of body weight was found: the vertical GRF increased almost three times when loads increased up to 20% of body weight compared to 10% of body weight. The anterior–posterior GRFs were asymmetrical when loads were increased. When carrying a load of 15% of body weight, all of the seven subjects adopted a compensatory trunk inclination. The emphasis on GRF and trunk inclination suggests that the safest load applied does not exceed 15% of body weight.

School Bag Weight and the Occurrence of Shoulder, Hand/Wrist and Low Back Symptoms among Iranian Elementary Schoolchildren

BACKGROUND

Schoolchildren usually use school bags to carry their school materials. Carry-ing heavy school bags can cause several problems such as musculoskeletal problems among schoolchildren. The aim of this study was to investigate the association between the weight of school bags and the occurrence of low back, shoulder and hand/wrist symptoms among pri-mary school children.

METHOD

This cross-sectional, descriptive-analytical study was conducted among a sample of 307 elementary school children in Tabriz, Iran. Data were collected using a questionnaire and from measurement of the school bag weight, body weight and height of each participant. Data were analysed using SPSS software.

RESULTS

The average load carried by schoolchildren was 2.9 kg, representing approximately 10% of the children's body weight. Girls and lower grade children carried a greater percent-age of their body weights. Approximately 86% of the children reported some kind of muscu-loskeletal symptoms. The occurrence of shoulder, wrists/hands, and low back pain among school-children was 70%, 18.5% and 8.7%, respectively. The results of binary logistic regres-sion indicated that the school bag weight (expressed as a percentage of body weight) was only significantly associated with hand/wrist symptoms (P<0.05). Girls were more likely to com-plaint from low back pain than boys were. Age was significantly negatively associated with hand/wrist symptoms. Body mass index was also significantly associated with shoulder symptoms.

CONCLUSION

The results indicate a high prevalence of musculoskeletal symptoms among elemen-tary schoolchildren. Preventive measures and appropriate guidelines with regard to safe load carriage in schoolchildren are therefore needed to protect this age group.

Effect of load mass on posture, heart rate and subjective responses of recreational female hikers to prolonged load carriage

Load carriage has been associated with a risk of upper and lower limb musculoskeletal disorders with women suffering significantly higher injury rates than their male counterparts. Despite this injury risk, there are limited evidence-based guidelines for recreational hikers, particularly female recreational hikers, regarding safe backpack loads. The purpose of the present study was to determine how variations in load mass affected the heart rate, posture and subjective responses of women during prolonged walking to provide evidence for a load mass limit for female recreational hikers. Heart rate (HR), posture and ratings of perceived exertion (RPE) and discomfort were collected for 15 female experienced recreational hikers (22.3 ± 3.9 years) while they hiked for 8 km at a self-selected pace under four different load conditions (0%, 20%, 30% and 40% of body weight (BW)). Although HR was not significantly affected by load mass or walking distance, increasing load mass and distance significantly affected posture, RPE and discomfort of the upper body. Carrying a 20% BW load induced significant changes in trunk posture, RPE and reported shoulder discomfort compared to the unloaded condition. The 20% BW load also resulted in a mean RPE rating of 'fairly light', which increased to 'hard' when carrying a 40% BW load. As load carriage distance increased participants reported significantly increased shoulder, neck and upper back discomfort. Based on the changes to posture, self-reported exertion and discomfort when carrying loads of 20%, 30% and 40% BW over 8 km, it was concluded that a backpack load limit of 30% BW should be recommended for female recreational hikers during prolonged walking.

Effects of sex and mode of carrying schoolbags on ground reaction forces and temporal characteristics of gait

The aim of this study was to examine the effects of different modes of carrying schoolbags on children. Ten girls and eight boys walked without a bag (NO-BAG), with a bag placed low at the back (LBACK), with a back placed high at the back (HBACK) and carrying the bag using the handle (HANDBAG). Ground reaction forces and temporal characteristics were recorded. When carrying a schoolbag, children walked with shorter strides, at lower speeds, with higher double support phase and increased vertical ground reaction forces compared with the NO-BAG condition (P<0.01). Compared with normal walking biomechanics, the HANDBAG condition showed the highest alterations, whereas the LBACK the least. Carrying the schoolbag by the handle has the largest effect on gait characteristics. Wearing backpacks by adjusting the shoulder straps to a loose position may reduce schoolbag effects.

Effects of a hip belt on transverse plane trunk coordination and stability during load carriage

This study examined the transverse plane kinematics of the pelvis, thorax and head while participants walked at a range of speeds on a treadmill under three load conditions: no load, with a loaded backpack with no hip belt and with a loaded backpack with a hip belt. Research has suggested that one mechanism for adapting to heavy loads carried with no hip belt is to reduce the amplitudes and relative phase of transverse plane pelvic and thoracic rotations, in order to minimize rotational torque on the loaded upper body. Transverse plane rotation amplitudes of the pelvis, thorax, backpack and head were calculated from 3D kinematic data for 12 healthy subjects, walking at speeds of 0.5, 0.9, 1.3 and 1.7 ms(-1). Relative phase relation and its variability were also computed for pelvis-thorax rotations and backpack-thorax rotations. Stability of the coordination pattern was estimated as an inverse function of the variability in relative phase. The backpack with the hip belt allowed significantly larger transverse plane rotation amplitudes, along with increased stability of the coordination pattern, than the backpack with no hip belt. Motion patterns of the backpack and thorax suggested that the backpack frame was used to assist with the deceleration and reversal of the loaded thorax, driven by the pelvis through the hip belt connection. Use of the frame in this way may have required less trunk muscle activation and allowed for improved pattern stability.

Postural and subjective responses to realistic schoolbag carriage

The objective of this study was to determine school student's postural and self-reported responses to realistic daily schoolbag carriage and to provide support for an upper schoolbag weight limit. Sixteen boys carried unloaded, 5%, 10%, 12.5% and 15% of body weight (BW) schoolbag loads, each for a simulated school day. The 10% BW condition was repeated with tightened shoulder straps. Participants' posture was quantified and a questionnaire asked them about a number of areas relating to the physical strain caused by each schoolbag. Posture, rating of perceived exertion (RPE) and muscular strain and ability to walk and balance were significantly affected when student's schoolbag load reached 10% BW. It is suggested that 15% BW may be excessive, which supports a schoolbag weight limit of 10% BW for a typical school day. Posture, RPE and muscular strain and ability to walk and balance were not significantly affected by the duration of carriage or by shoulder strap tightness.

Ergonomics in schools

This Special Issue on Ergonomics in Schools is dedicated to the memory of my co-guest editor Cheryl Bennett who sadly and unexpectedly passed away peacefully on 2 July 2007 - only 10 days before this editorial was completed. Cheryl was inspirational in her vigorous championing of this new area of ergonomics activity, most prominently and to great effect through her foundation chairmanship of the International Ergonomics Association (IEA) Technical Committee on Ergonomics for Children in Educational Environments (ECEE) (see www.iea.cc).

Measurement of the temporal patterns of school bag carriage using activity monitoring and structured interview

The primary objective of the current study was to quantify the temporal patterns of school bag carriage over an actual school day using activity monitoring and structured interviews, in order to better understand the physical demands of school bag carriage. The temporal patterns of 40 students' school bag carriage over a 24-h period were defined by total school bag carrying time, mean event school bag carrying time, the number of school bag carrying events, total carrying time travelling to and from school and the number of students who walked or used transport to travel to and from school. There were significant correlations between activity monitor [mean(SD) 119(48) min] and structured interview [100(39) min] determined total school bag carrying time (r = 0.59), activity monitor [8(4) min] and structured interview [9(4) min] determined mean event school bag carriage time (r = 0.65), and activity monitor [15(4) events] and structured interview [11(2) events] determined number of school bag carrying events (r = 0.52). However, the number of school bag carrying events, and for students who used transport, the total amount of time spent travelling to school was significantly different using the two measures. The durations of school bag carriage and the relationship between activity monitor and structured interview were similar to those reported in previous studies.

Back pain in school children--where to from here?

Back pain is now recognised to occur early in childhood and is associated with high prevalence rates when estimated by survey. This review paper considers the risk factors associated with back pain in children aged 11-14 years, and particularly those present in a school setting. The risk factors most significantly associated with back pain are primarily characteristics of the individual with less strong associations with factors present in the school environment. The majority of intervention studies undertaken in a school setting have focussed on the effect of school furniture on posture and comfort and were of short-term duration. There is a need for further research in order to achieve a better understanding of the risk factors present in a school environment and to address ways to reduce the currently recognised perceived problem of back pain among school children. A strategy for an evidence-based longitudinal intervention study is proposed, with the content outlined under the headings: policy, school equipment and furniture, individual and family.