Effect of prolonged walking with backpack loads on trunk muscle activity and fatigue in children

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.

Differences in walking and running parameters in elementary school students with and without backpacks

BACKGROUND

Backpack syndrome (BS) is a term used to describe symptoms such as shoulder and back pain that are believed to be caused by carrying a backpack. Few studies have investigated the changes in walking and running parameters with and without backpacks.

OBJECTIVE

The present study aimed to investigate the differences in walking and running parameters with and without backpacks in primary school children with and without BS.

METHODS

This cross-sectional study included 51 children (average age 9.3 years, 6- 12 years). Two questions were asked beforehand: whether the respondents had shoulder or back pain when going to school and present; those who answered that they had pain in both cases were defined as the BS group, while the others were the control group. Walking and running at comfortable speeds and walking and running with a 6 kg backpack on their backs were measured.

RESULTS

During walking, there were main effects for speed, cadence, and strike angle with and without the backpack, but no interactions were identified for any of the parameters. In running, however, there were main effects for speed, stride length, strike angle, and lift-off angle, and an interaction effect was observed for speed and stride length.

CONCLUSIONS

During walking, carrying a 6 kg backpack increased cadence and walking speed. During running, carrying a backpack caused a decrease in stride length and running speed in the BS group, whereas there was no change in the control group, suggesting that the control and BS groups may respond differently.

Influence of Backpack Carriage and Walking Speed on Muscle Synergies in Healthy Children

Four to five muscle synergies account for children's locomotion and appear to be consistent across alterations in speed and slopes. Backpack carriage induces alterations in gait kinematics in healthy children, raising questions regarding the clinical consequences related to orthopedic and neurological diseases and ergonomics. However, to support clinical decisions and characterize backpack carriage, muscle synergies can help with understanding the alterations induced in this condition at the motor control level. In this study, we investigated how children adjust the recruitment of motor patterns during locomotion, when greater muscular demands are required (backpack carriage). Twenty healthy male children underwent an instrumental gait analysis and muscle synergies extraction during three walking conditions: self-selected, fast and load conditions. In the fast condition, a reduction in the number of synergies (three to four) was needed for reconstructing the EMG signal with the same accuracy as in the other conditions (three to five). Synergies were grouped in only four clusters in the fast condition, while five clusters were needed for the self-selected condition. The right number of clusters was not clearly identified in the load condition. Speed and backpack carriage altered nearly every spatial-temporal parameter of gait, whereas kinematic alterations reflected mainly hip and pelvis adaptations. Although the synergistic patterns were consistent across conditions, indicating a similar motor pattern in different conditions, the fast condition required fewer synergies for reconstructing the EMG signal with the same level of accuracy.

Causality of occupational exposure on rheumatoid arthritis and ankylosing spondylitis: a two-sample mendelian randomization study

Objective

This study aimed to explore the potential causal link between three specific types of occupational exposure on rheumatoid arthritis (RA) and ankylosing spondylitis (AS).

Method

A Two-sample Mendelian randomization (TSMR) analysis, comprising univariate MR (UVMR) and multivariate MR (MVMR) analyses, was performed to investigate the potential causal association between three types of occupational exposures, jobs involving mainly walking or standing (JWS), jobs involving heavy manual or physical work (JMP), and jobs involving shift work(JSW) on RA and AS. Genetic variants for genome-wide association studies (GWAS) of occupational exposure and AS were obtained from the UK Biobank. GWAS summary data for RA were obtained from FinnGen Biobank analysis. For UVMR, six methods of Inverse Variance Weighted (IVW), MR-Egger, Weighted Mode, Weighted Median, Simple Mode, MR pleiotropy residual sum, and outlier (MR-PRESSO) were used for the analysis. The MVMR was analyzed using the IVW model as well as the MR-Egger model.

Results

The UVMR suggested no causal relationship between the three occupational exposure and RA [IVW: P=0.59,0.21,0.63] or AS [IVW: P=0.43,0.57,0.04], as did the bidirectional MR [IVW: P=0.73,0.70,0.16], [IVW: P=0.65,0.68,0.74]. Although unadjusted MVMR suggested a causal relationship between JMP and AS [IVW: OR = 1.01, 95% CI = 1.00- 1.02, p = 0.02], the adjusted MVMR denied this relationship and concluded that there was no causal relationship between the other occupational exposure and either RA or AS.

Conclusion

Our MR analysis did not establish a direct causal relationship between certain occupational exposures and either RA or AS.

Influences of dynamic load phase shifts on the energetics and biomechanics of humans

Using load-suspended backpacks to reduce vertical peak dynamic load exerted on humans can reduce metabolic costs. However, is it possible to further reduce metabolic cost by modulating dynamic load phase shift? If so, is anti-phase better than the others? In this study, we investigated the biomechanics, energetics and trunk response under phase shifts. Nine subjects wearing an active backpack with 19.4 kg loads walked on a treadmill at 5 km h-1 with four phase shift trials (T1-T4) and a load-locked trial (LK). Our results show that anti-phase trial (T3) assists ankle more and reduces the moment and gastrocnemius medialis activity, while T4 assists knee more and reduces the moment and rectus femoris activity. Due to the load injecting more mechanical energy into human in T3 and T4, the positive centre-of-mass work is significantly reduced. However, the gross metabolic rate is lowest in T4 and 4.43% lower than in T2, which may be because the activations of erector spinae and gluteus maximus are reduced in T4. In addition, T3 increases trunk extensor effort, which may weaken the metabolic advantage. This study provides guidance for improving assistance strategies and human-load interfaces and deepens the understanding of the energetics and biomechanics of human loaded walking.

The Influence of the Weight of the Backpack on the Biomechanics of the Child and Adolescent: A Systematic Review and Meta-analysis With a Meta-Regression

PURPOSE

To evaluate and explore the influence of the weight of a backpack on standing posture and gait in children and adolescents.

METHODS

We conducted a search of MEDLINE (PubMed), Cochrane Library, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Web of Science, with the last search in July 2021. Standardized mean differences (SMD) and 95% confidence intervals were calculated for relevant outcomes and were pooled in a meta-analysis using the random-effects model. The participants were healthy children or adolescents. The outcomes were postural variables, spatiotemporal gait variables, gait kinematics, and muscle activity. We analyzed the influence of a loaded backpack on posture while standing and spatiotemporal and kinematic variables while walking. We used GRADE, Risk of Bias 2, ROBINS-I, MINORS, and PEDro scales to rate the quality, certainty, and applicability of the evidence.

RESULTS

Wearing a loaded backpack induces a significant increase of the craniohorizontal angle while standing and a decrease of walking speed and stride length while walking. Only the craniovertebral angle had a significant relationship with the weight of the backpack.

CONCLUSIONS

Wearing a backpack induces postural changes while standing and affects gait in children and adolescents; however, almost all the changes are not related to the backpack weight.

Prevalence of Thai People with Lumbar Instability and Associated Factors: A Cross-Sectional Study

Background

Lumbar instability has been extensively reported; however, the risk factors for lumbar instability remain poorly defined, and understanding this condition better would help health professionals and their patients.

Proposal

To determine the prevalence of lumbar instability in Thai people with chronic low back pain (CLBP) and explore the factors associated with lumbar instability in these patients.

Patients and Methods

Using multistage random sampling methods, 1762 participants with CLBP were enrolled in the study from six regions of Thailand. Data were collected using a paper-based questionnaire. Participants were interviewed by physical therapists in the hospital they attended. They were classified as having lumbar instability when they attained ≥7/14 items on the lumbar instability screening tool. Univariate and multivariate regression analysese were used to determine the possible factors associated with lumbar instability.

Results

There were 961 (54.54%) participants with lumbar instability and 801 (45.46%) participants without. The eight factors associated with lumbar instability were: (i) age ≥40 years (AOR: 1.36; 95% CI: 1.09-1.69); (ii) body mass index ≥25 kg/m² (AOR: 1.42; 95% CI: 1.16-1.74); (iii) having an underlying disease (AOR: 1.32; 95% CI: 1.06-1.65); (iv) frequent lifting ≥5 kg in occupational habits (AOR: 1.69; 95% CI: 1.36-2.09); (v) prolonged walking ≥4 hours per day (AOR: 1.31; 95% CI: 1.04-1.64); (vi) gardening in leisure time (AOR: 1.37; 95% CI: 1.10-1.71); (vii) other area of pain (AOR: 1.24; 95% CI: 1.01-2.52): and (viii) other area of numbness (AOR: 1.85; 95% CI: 1.50-2.27). When considering only women, prior pregnancy was associated with lumbar instability with OR of 1.76 (95% CI: 1.36-2.22), p-value <0.0001.

Conclusion

When treating patients with CLBP who are suspected to have lumbar instability, healthcare professionals should consider associated factors that might be modifiable targets for interventions to improve outcomes.

Evaluation of an ergonomically designed schoolbag: Heart rate variability and body discomfort rating

BACKGROUND: Unsuitable schoolbags may stress the spine and promote poor body posture, particularly for school students. Global recommendations have suggested that schoolbag weight must not exceed 10% of a healthy student’s body mass, which would need continuous monitoring and enforcement. OBJECTIVES: The present study presents a comparison between an ergonomically designed schoolbag, which helps reduce the potential effects of carrying a load, and a commercial one. METHODS: A total of 30 healthy male students were recruited for this experiment. Independent variables determined were schoolbag type (ergonomically designed and commercial schoolbags) and three load levels based on body mass percentage (i.e., 10%, 15%, and 20% of body mass). Heart rate variability (HRV) and body discomfort rating were then measured. RESULTS: Our results showed that the developed schoolbag promoted enhanced subjective measures and HRV response at 15% and 20% of body mass. Participants who wore the developed schoolbags experienced significantly lesser neck, shoulder, upper and lower trunk discomfort than those who wore the traditional ones. Changing the load percentage from 10% to 15% caused an increase in heart rate among participants carrying a commercial schoolbag but a decrease in heart rate among those carrying the developed schoolbag. CONCLUSIONS: The findings presented herein suggest introducing strategies for reducing the potential impact of load carrying through the combined effect of new educational inventions and policy changes.

Effects of backpack-induced fatigue on gait ground reaction force characteristics in primary school children with flat-foot deformity

This study aimed to assess the effects of backpack carriage in different weights and muscle fatigue on the GRF components in primary school children with flat-foot deformity. The GRF components from 42 primary school children (21 with low arch, and 21 with normal) were collected before and after backpack-induced fatigue protocol during shod walking with backpacks in weight 7.5, 10, 12.5 and 15% of the child's bodyweight. The amplitudes of Fx2 of 10%BW and Fz3 of 7.5%BW in the flatfeet group were less than in the healthy group without fatigued condition. (P < 0.05). After fatiguing, the amplitudes of Fx2 of 7.5%BW, Fz3 of 12.5 and 15%BW were significantly decreased in the low arch group than those in the healthy subjects (P < 0.05). Within-group comparisons of measured Fx2 of 10%BW, Fy1 (7.5,10 and 15%BW), Fy2 of 7.5%BW, FZ1 (7.5,10 and 15%BW), FZ2 (7.5,10 and 15%BW), and TTP of TFz1 of 7.5%BW, TFz3 (7.5,10 and 12.5%BW), Loading rate (7.5,10 and 15%BW) were significantly different from pre- to post-fatigue in the flatfeet group(P < 0.05). Within-group comparisons of measured Fy1 of 10%BW, Fy2 (7.5% and 10%BW), FZ1 (7.5% and 10%BW), FZ2 (7.5% and 10%BW), and TTP of TFz3 of 7.5%BW, Loading rate (7.5% and 10%BW) were significantly different from pre- to post-fatigue in the healthy group (P < 0.05). It seems that TTP of GRF variables does have clinical importance for rehabilitation of flatfeet deformity. Carrying heavy backpacks and backpack-induced fatigue had different effects on GRF characteristics among children with low and normal foot arch.

Energy cost of walking and body composition changes during a 9-month multidisciplinary weight reduction program and 4-month follow-up in adolescents with obesity

The purpose of the present study was to investigate changes in the energy cost of locomotion during walking (Cw) related to changes in body mass (BM, kg) and body composition in adolescents with obesity. Twenty-six (12 boys and 14 girls) obese adolescents (mean: body mass index, 33.6 ± 3.7 kg·m-2; 42.7 ± 4.5% fat mass (FM)) followed a 9-month multidisciplinary inpatient weight-reduction program consisting of lifestyle education, moderate energy restriction, and regular physical activity in a specialised institution. At baseline (M0), the end of the 9-month program (M9), and after the 4-month follow-up (M13), oxygen consumption and carbon dioxide production of the standardised activity program were assessed by whole-body indirect calorimetry over 24 hours, and body composition was assessed by dual-energy X-ray absorptiometry. At M9, adolescents showed an 18% reduction in BM (p < 0.001) and 40% in total FM, while fat-free mass (kg) remained stable in boys but decreased by ∼6% in girls (p = 0.001). Similarly, the mean Cw decreased by 20% (p < 0.001). At M13, BM, FM, and Cw were slightly higher compared with at M9. In conclusion, moderate energy restriction and regular moderate physical activities improved walking economy, improved exercise tolerance, and induced beneficial changes in the body composition of adolescents with obesity. Novelty: Reduction of FM in the trunk region, and consequently reducing the work carried out by respiratory muscles, contributes to reducing Cw in adolescents with obesity. A lower walking cost can be effective in improving exercise tolerance and quality of life in obese adolescents.

The Influence of External Additional Loading on the Muscle Activity and Ground Reaction Forces during Gait

Asymmetrical external loading acting on the musculoskeletal system is generally considered unhealthy. Despite this knowledge, carrying loads in an asymmetrical manner like carrying on one shoulder, with one hand, or on the strap across the torso is a common practice. This study is aimed at presenting the effects of the mentioned load carrying methods on muscle activity assessed by using thermal field and ground reaction forces. Infrared thermography and pedobarographic force platform (ground reaction force/pressure measurement) were used in this study. Experimental results point out an increased load-dependent asymmetry of temperature distribution on the chosen areas of torso and the influence of external loading on ground reaction forces. Results point out that wearing an asymmetrical load should be avoided and are showing which type of carrying the external load is potentially less and the most harmful.

Allowing the Load to Swing Reduces the Mechanical Energy of the Stance Leg and Improves the Lateral Stability of Human Walking

Loaded walking with typical rigid backpack results in a significant increase in the mechanical energy of the stance leg and a decrease in lateral stability. Allowing the load to swing, which has been applied in shoulder pole, a tool widely used in Asia for load carriage assistance, may attenuate these effects. This paper theoretically analyzes and experimentally validates the biomechanical and energetic effects of the swinging loads. When walking with a 30 kg load, allowing the load to swing reduces the fore-aft leg impulses by over 19% and further reduces the mechanical energy of the stance leg by 12.9% compared to the typical rigid backpack. The whole-body metabolic cost has no significant change, which may be attributed to the increase in the muscle work of the upper body and the leg swing. Moreover, the load movement out of phase to the human in the lateral direction reduces the lateral excursion of extrapolated center-of-mass by 27.2%, indicating an increase in the lateral margin of stability and implying an improvement in lateral stability. The results demonstrate that allowing the load to swing reduces the horizontal leg impulses and the mechanical energy of the stance leg, and improves the lateral stability of human walking.

Remote Actuation Systems for Fully Wearable Assistive Devices: Requirements, Selection, and Optimization for Out-of-the-Lab Application of a Hand Exoskeleton

Wearable robots assist individuals with sensorimotor impairment in daily life, or support industrial workers in physically demanding tasks. In such scenarios, low mass and compact design are crucial factors for device acceptance. Remote actuation systems (RAS) have emerged as a popular approach in wearable robots to reduce perceived weight and increase usability. Different RAS have been presented in the literature to accommodate for a wide range of applications and related design requirements. The push toward use of wearable robotics in out-of-the-lab applications in clinics, home environments, or industry created a shift in requirements for RAS. In this context, high durability, ergonomics, and simple maintenance gain in importance. However, these are only rarely considered and evaluated in research publications, despite being drivers for device abandonment by end-users. In this paper, we summarize existing approaches of RAS for wearable assistive technology in a literature review and compare advantages and disadvantages, focusing on specific evaluation criteria for out-of-the-lab applications to provide guidelines for the selection of RAS. Based on the gained insights, we present the development, optimization, and evaluation of a cable-based RAS for out-of-the-lab applications in a wearable assistive soft hand exoskeleton. The presented RAS features full wearability, high durability, high efficiency, and appealing design while fulfilling ergonomic criteria such as low mass and high wearing comfort. This work aims to support the transfer of RAS for wearable robotics from controlled lab environments to out-of-the-lab applications.

Kinesiotaping Techniques to Alter Static Load in Patients With Foot Pronation

Objective

This study aimed to assess the effect of kinesio tape (KT) application on foot pronation using the laser postural alignment system.

Methods

Twenty participants (10 females and 10 males, mean age 19.7 ± 1.2 years) with foot pronation were included in the study. The laser line projected on the participant by the laser postural alignment system showed the joint load carrying line. The location of the joint load carrying line was assessed during barefoot static standing with one foot on the force plate before KT application, immediately after application, then 24 and 48 hours later. Displacement of the load-carrying line was measured using a ruler placed tangentially to the patella and ankle joint at the level of the joint line. Weight bearing on the barefoot was assessed before KT application, immediately after, then 24 and 48 hours later.

Results

Weight bearing was not significantly changed after KT application. The load-carrying line measured using KT did not notably move with KT versus without KT in the ankle joint. Immediately after KT application, significant lateral knee joint movement was measured, but this change was not importantly 24 and 48 hours later.

Conclusion

KT was not altered in changing weight bearing or moving the lower extremity load-carrying line in people with foot pronation. KT of the foot can amplify sensory input and improve perceived comfort; therefore, it can be used with an orthotic insole in footwear.

A Screening Tool for Patients With Lumbar Instability: A Criteria-related Validity of Thai Version

STUDY DESIGN

The study is a cross-sectional, diagnostic validity study.

OBJECTIVE

The aim of this study was to examine the performance characteristics and validity of an existing lumbar instability questionnaire as a screening tool for lumbar instability among chronic low back pain (CLBP) patients.

SUMMARY OF BACKGROUND DATA

Lumbar instability is an initial stage of more severe spinal pathology. Early screening for this condition should help prevent more structural damage. To meet this need, the present study developed numerical cutoff scores for the lumbar instability screening tool.

METHODS

Lumbar instability screening tool responses and x-ray assessments were reviewed from a sample of 110 patients with CLBP (aged 20-59 years). Receiver operator curves were constructed to optimize sensitivity and specificity of the tool.

RESULTS

Fourteen (12.73%) patients had radiological lumbar instability. These patients reported a higher mean lumbar instability questionnaire score than those without radiological lumbar instability. A questionnaire score of at least 7 had a sensitivity of 100% (95% CI, 100-100) and a specificity of 26.04% (95% CI = 17.84-34.24) for detecting lumbar instability when compared with x-ray examination. Receiver operator curve analysis revealed the lumbar instability screening had an area under the curve of 0.62 (95% CI, 0.47-0.77).

CONCLUSION

A lumbar instability screening tool total score of at least 7 was ruled out lumbar instability in CLBP patients. This cutoff score may be used as a marker of conservative treatment response. The sample size of patients with lumbar instability in this study was small, which may hinder the reliability of the data. Further studies are needed.

LEVEL OF EVIDENCE

4.

Development and Experimental Verification of an Ergonomic Backpack

Carrying a heavy school backpack has extensively been reported as a prime cause of children's body strain. It is suggested that the load should not exceed 10 percent of the child's body weight; however, ensuring this requires continuous monitoring. The study explores how ergonomically designed school backpack based on the user anthropometric data (n = 280) and ergonomic parameters help reduce force concentration on shoulders and back. It provides a validation process of the developed prototype by experimental verification. The developed design was assessed in a comparison experiment with a commercially available local school backpack. An experimental study was used which recruited thirty healthy college students (aged 19 to 23 years). Two independent variables evaluated were school backpack type (developed backpack versus commercial one) and load levels as a percentage of body weight. Three load levels were employed 10%, 15%, and 20%. These variables were measured on the responses: bag comfort scale and the percent of maximum voluntary contraction (%MVC) of six muscles (right and left of erector spine, right and left of external abdominal oblique muscle, and right and left of trapezius). The developed backpack provided astonishing performance at levels of 15% and 20% of body weight in terms of subjective measure and electromyography (EMG) responses. It also showed that increasing the carried weight more than 10% result in reducing activity on the erector spinal muscles, while it increases on abdominal oblique muscles. The developed backpack design confirmed the efficiency of its bases by distributing the carried weight among the trunk through side pockets, attached to the body through two upper and lower straps. It helped the body to distribute the carried weight and avoid concentrating pressure on specific areas.

Validity of different EMG analysis methods to identify aerobic and anaerobic thresholds in speed skaters

PURPOSE

This study aimed to assess the validity of the first (EMGth1) and second (EMGth2) breakpoints in the EMG signal during skating.

SCOPE

Ten well-trained long track speed skaters performed a maximal incremental skating test on a slide board. EMG signals from six lower limb muscles were recorded during the last 15 s of each stage and converted to Root Mean Square for determination EMGth1 and EMGth2 using mathematical (2 and 3 linear regressions) and visual methods.

CONCLUSIONS

EMGth1 had a low detection rate (<50%) while EMGth2 could be identified visually in > 80% of cases, in 85% of cases using 2-lines and 63% using 3-lines regression. Quads (VL + VM) and Gluts (GM + GMd) had the highest EMGth2 detection rate for all methods (>70%). EMGth2 from Quads and Gluts detected by the 2-lines and 3-lines regression were not different than the second ventilatory threshold (VT2) (p > 0.05), while the visual method overestimated VT2 (p < 0.01). EMGth2 detected from Quads by the 2-lines regression method presented better correlation with VT2 stage (r = 0.91), lowest bias, and limit of agreement. We conclude that EMG is a valid non-invasive method to detect VT2 during skating when using a mathematical method to determine EMGth2.

The metabolic demand of external load carriage in golfers: a comparison of a single versus double-strap golf bag

BACKGROUND

A golf bag filled with a set of clubs provides a substantial load. When carried over distance this can increase the demands placed upon the golfer, leading to discomfort, fatigue and injuries. This study aimed to compare the metabolic demands of 2 methods of golf bag carriage.

METHODS

A total of 16 healthy male recreational golfers participated in the study. Participants were given an initial familiarization session in which their self-selected walking speed was determined. This was utilized as the treadmill speed for all subsequent trials. The testing protocol consisted of 3 randomized trials of treadmill walking for 5 minutes in each of three conditions: unloaded, single-strap bag and double-strap bag. Equipment consisted of a double-strap golf bag with a standard set of clubs weighing 12.5kg. For all trials oxygen consumption (L·min-1), VO2 (mL·kg·min-1) respiratory minute volume (VE) (L·min-1), and heart rate (HR) were measured.

RESULTS

Results showed that the double-strap bag required significantly less oxygen consumption (1.19±0.19 vs. 1.31±0.16 L·min-1, P<0.01) relative oxygen consumption (14.49±2.06 vs. 15.93±2.25 mL·kg·min-1, P<0.01), reduced respiratory minute volume (29.95±4.19 vs. 32.47±4.26 L·min-1, P<0.05), and lower heart rates (100.14±11.05 vs. 106.96±9.33 BPM, P<0.001) than the single-strap bag. Both methods of carriage showed significantly greater metabolic demands than the unloaded condition (P<0.05).

CONCLUSIONS

The decreased metabolic cost of carrying a double-strap golf bag may facilitate a reduction in fatigue and reduced mechanical stress. Golf bag transportation must therefore be recognized as a factor in reducing the risk of injury and improving playing performance.

Factors associated with non-specific low back pain in children aged 10-12 from Bucaramanga, Colombia: A cross-sectional study

BACKGROUND

There are no Colombian studies published that assess non-specific low back pain (NSLBP) risk factors in children.

OBJECTIVE

To determine the factors associated with NSLBP in 73 children (19.2% girls) aged 10-12 years in one military school in Bucaramanga, Colombia.

METHODS

A questionnaire was used to obtain information of risk factors. Subsequently, children's weight and height were measured. The backpack was weighed at the beginning of each day from Monday to Friday. Crude and adjusted prevalence ratios were calculated, with their respective 95% confidence interval (CI).

RESULTS

The one-month prevalence of NSLBP was 39.7% (95% CI 28.4-51.9). In the multivariate analysis, carrying backpacks wearing between 12% and 20% of body weight, having a perception that the backpack is very heavy, and being a passive smoker increase the likelihood of NSLBP, while being 11-year-old compared to 10-year-old decreases the likelihood of having NSLBP, adjusted for gender, body mass index, and history of LBP in parents.

CONCLUSIONS

High prevalence of low back pain was found in children between 10 and 12 years old. The study of the decisive factors of low back pain is important to identify children at risk, as well as to develop efficient primary prevention programs.

Comparison between the Physiological Responses and Subjective Ratings of a Group of Male Students to Three Backpack Designs

It is important for schoolchildren and their parents (or guardians) to know which backpacks exert the least strain on the cardiorespiratory system. In this study, we investigated the physiological responses of participants while they were walking on a treadmill and wearing one of three different backpacks (A, B, and C) under two different load-carrying conditions (equivalent to 10% and 15% of their body mass, respectively). The first condition was used as a control and involved walking without a backpack, while the second involved wearing a backpack and carrying a certain weight. Thirty-one male students from King Saud University walked on a treadmill at 0.861 m/s and at a 0% inclination angle, while having their heart rates (beatsmin⁻¹), oxygen uptakes (VO2, mLmin⁻¹), respiratory rates (breaths, VO2min⁻¹), perceived exertion rates (PER, Borg scale), and backpack preference rates (BPR) measured and recorded. The results of our within-subject experimental design revealed that the physiological results varied significantly depending on the type of backpack. Backpacks B and C were superior to Backpack A, resulting in lower physiological responses and higher subjective preferences. Students carrying more weight experienced higher physiological stress; moreover, the use of Backpack C led to the lowest physiological strains and higher subjective preferences.

The effect of backpack load placement on physiological and self-reported measures of exertion

BACKGROUND

Backpacks are the most popular way of carrying additional weight; however, it puts the body under physical stress and may cause discomfort. It may also increase oxygen demand and energy cost. Manipulation of load placement may relieve the effects carrying a backpack has on the body.

OBJECTIVE

This study investigated physiological and self-reported measures of exertion, movement economy and efficiency, carrying a loaded backpack in high and low load placement compared to a control condition.

METHOD

Fifteen healthy adults were examined under three load conditions: no load, carrying a 20% of body weight in high and low load placement. Dependent variables were measured using a metabolic measurement system and participants rated their perceived exertion on a Borg scale.

RESULT

Carrying load produced a significant increase in VO2, minute ventilation, heart rate, movement economy and overall perceived exertion in both load placements compared with the no backpack condition. However, no difference was observed between the high and low load placement conditions.

CONCLUSION

While altering load placement did not influence physiological variables or overall exertion, participants reported lower perceived exertion on the shoulders in low load placement and low load placement might be preferable in this respect.

The Impact of Backpack Loads on School Children: A Critical Narrative Review

Background: Backpack loads of school students during school days have been suggested to range from 10% to as high as 25% of their body weight and may have a negative impact on their body. The aim of this review was to identify and review studies that have examined impacts of contemporary backpack loads on school children. Methods: A systematic search was conducted of the literature using key search terms. After relevant studies published in recent years were selected using strict inclusion and exclusion criteria, the studies were critically appraised and relevant data were extracted and tabulated prior to conducting a critical narrative synthesis of findings. Results: Twenty-one studies were included, ranging in methodological quality from poor to good (critical appraisal scores 22% to 77%). Students carried on average over 15% of their own body weight, which caused biomechanical and physiological adaptations that could increase musculoskeletal injury risk, fatigue, redness, swelling and discomfort. Conclusion: Considering the limited methodological quality and variations in foci across studies, further research is needed to elucidate: (1) the loads students carry around on a school day in their school backpacks and; (2) the biomechanical, physiological and physical effects of load carriage on students.

Effect of slipper wearing and carrying positions of infant on dynamic stability and kinetic variable during level walking

Recently though various hip seats for carrying infant of women was designed and developed, then, wearing slipper may restrain the movement of bare foot. The study was undertaken to investigate the dynamic stability and kinetic variables according to between position of carrying infant and wearing slipper. Adult female (n=10) and under one year age of infant (n=10) participated in the study. Extrapolated center of mass, center of pressure, ground reaction force (GRF), and leg stiffness of gait characteristics using 3-dimensional cinematography and GRF were analyzed. Dynamic stability according to position of carrying infant and wearing slipper was not significant. While when carried an infant against normal gait showed significant difference in breaking force, leg stiffness and loading rate (P<0.001). Of which breaking force and vertical impulse were more increased when the back-carried against fore-carried of trunk. Thus it resulted in transformation on types of impulse transfer to leg and COG of women’s carrying infant, which may be strategy for securing a dynamic stability. Therefore experts related with exercise rehabilitation should understand sufficiently on gait characteristics of women with diseases on muscular-skeletal system and perform effective rehabilitation and treatment.

Muscle-specific endurance of the trapezius muscles using electrical twitch mechanomyography

BACKGROUND

Symptoms of fatigue and pain are often reported for the trapezius muscle in the shoulder. The present study evaluated endurance in the trapezius muscles of healthy participants using electric twitch mechanomyography (ETM).

METHODS

Surface electrodes and a tri-axial accelerometer were placed over the left trapezius muscle. Muscles were stimulated for 3 min each at 2 Hz, 4 Hz and 6 Hz. Maintenance of acceleration during muscle twitches was used to calculate an endurance index (EI). Subjects (n = 9) were tested on two separate days to assess reproducibility of the trapezius EI measurements. The endurance measurements were made on the wrist flexor and vastus lateralis muscles for comparison. Near infrared spectroscopy was used to measure muscle oxygenation (HbO₂) during the stimulation protocol (n = 8).

RESULTS

Mean (SD) EI was 84.9% (8.7%), 63.3% (19.1%) and 41.7% (20.0%) for 2 Hz, 4 Hz and 6 Hz, respectively. The coefficients of variation were 7.4%, 11.3% and 24.0% for 2 Hz, 4 Hz and 6 Hz, respectively. EI values were significantly lower in the trapezius compared to arm and leg muscles (p < 0.05). HbO₂ values were unchanged from resting values with electrical stimulation.

CONCLUSIONS

The EI as measured by ETM may provide a reproducible method of evaluating function in trapezius muscles that is not influenced by oxygen saturation.

The Effect of Backpack Load Carriage on the Kinetics and Kinematics of Ankle and Knee Joints During Uphill Walking

The purpose of this study was to investigate the effect of load carriage on the kinematics and kinetics of the ankle and knee joints during uphill walking, including joint work, range of motion (ROM), and stance time. Fourteen males walked at a self-selected speed on an uphill (15°) slope wearing military boots and carrying a rifle in hand without a backpack (control condition) and with a backpack. The results showed that the stance time significantly decreased with backpack carriage (p < .05). The mediolateral impulse significantly increased with backpack carriage (p < .05). In the ankle joints, the inversion-eversion, and dorsi-plantar flexion ROM in the ankle joints increased with backpack carriage (p < .05). The greater dorsi-plantar flexion ROM with backpack carriage suggested 1 strategy for obtaining high plantar flexor power during uphill walking. The result of the increased mediolateral impulse and inversion-eversion ROM in the ankle joints indicated an increase in body instability caused by an elevated center of mass with backpack carriage during uphill walking. The decreased stance time indicated that an increase in walking speed could be a compensatory mechanism for reducing the instability of the body during uphill walking while carrying a heavy backpack.

Backpack-back pain complexity and the need for multifactorial safe weight recommendation

The study analysed backpack-related back pain in school children by investigating the possibility of multiple interactions among causative factors, which may be responsible for the non-conclusive findings on the issue. Using data from 444 prepubescent schoolchildren, a mixed method design combining survey, observation and direct measurement strategies was implemented. Using a multivariate structural equation modelling approach, the study investigated interactions among anthropometry, posture, backpack volume, rating and back pain constructs, with each construct made of 2-4 indicators. Additionally, regression analysis was used to determine the feasibility of considering the two additional factors of age and body mass index along with the globally accepted recommendation of a load of 10-15% of body weight. Our model demonstrated an acceptable model fit and revealed direct and indirect effects of the factors. Obese children were recommended to carry a one-third lighter load than other children. The application of systematic/multiple strategies provided an explanation for some of the issues associated with school children's backpack-related back pain.

Interaction of body mass index and age in muscular activities among backpack carrying male schoolchildren

BACKGROUND

The complex and limited understanding of the interactions among multiple factors associated with back pain occurrence among schoolchildren might explain the current inconclusive and contradictory findings on the issue. The global increase in the prevalence of childhood overweight and obesity, which reportedly affects children's physical abilities, calls for concern among school/children ergonomists and other stakeholders.

OBJECTIVE

The study investigated the interaction of body mass index (BMI) and age on the muscular activities, backpack height and perceived level of pain arising from carrying different weight of backpacks.

METHODS

Surface electromyography analysis of erector spinae and trapezius muscular activities was conducted on 47 primary schoolchildren aged between 8 and 11 years. Repeated measure ANOVA were carried out on the data.

RESULTS

There was significant difference in all the measures of muscular activities, backpack height and pain rating at different levels of backpack weight. However, the children were only significantly fatigable in the erector spinae muscles of the lower back and not in the trapezius of the upper back. The interactive effect of BMI was more pronounced than the children's age.

CONCLUSIONS

The study shows that it is not appropriate for all schoolchildren to have the same backpack weight limit and obese schoolchildren should carry a lower bag-to-body ratio of backpack weight. The younger children also need an appropriate bag surface-to-trunk ratio size of backpack as they were more affected by the position of the backpack.

The response of the body when carrying a handbag

BACKGROUND

Carrying a load in hand is commonly seen in daily life. There were many studies investigating the optimal weight when carrying a backpack, however, only a few studies investigated optimal weight when carrying a bag in different ways.

OBJECTIVE

To investigate the optimal weight for carrying a handbag.

METHODS

This study involved 13 healthy females, randomized into four carrying weight patterns [no load, bag weight of 5% body weight (BW), 7% BW, and 10% BW] who were walking barefoot on the platform at preferable speed. The center of pressure (COP) was collected by the platform. Spinous processes of C7, T1, T12, L1, S2 and the right tragus were attached with markers. The muscle activities of upper trapezius, erector spinae, and rectus abdominis muscles were measured. All data including discomfort scale were recorded.

RESULTS

The spinal curvature was not affected from carrying a handbag. However, the COP trend was toward the carrying side when carrying a greater load. Asymmetrical activities of the upper trapezius and erector spinae were shown (p < 0.05). The discomfort areas were the right upper trapezius and right finger flexor muscles.

CONCLUSIONS

Continuously carrying a handbag greater than 10% BW can cause musculoskeletal problems.

Walking With aBackpack Using Load Distribution and Dynamic Load Compensation Reduces Metabolic Cost and Adaptations to Loads

In this study, we showed a way of reducing the metabolic cost of walking with a backpack using load distribution and dynamic load compensation, provided by a wearable upper body device. This device distributes the backpackload between the shouldersand the pelvis, senses the vertical motion of the pelvis, and provides gait synchronized compensatory forces to reduce the dynamic loads from a backpack. It was hypothesized that by reducing dynamic loads from a backpack during load carriage, the user's gait and postural adaptation, muscular effort and metabolic cost would be reduced. This hypothesis was supported by biomechanical and physiological measurements on a group of young healthy subjects, as they walked on a treadmill under four different conditions: unloaded; with a backpack, loaded with 25% of their body weight, supported on the shoulders; with the same load distributed between the shoulders and the pelvis; and with dynamic load compensation in addition to load distribution. The results showed reductions in gait and postural adaptations, muscle activity, vertical and braking ground reaction forces, and metabolic cost while carrying the same backpack load with the device. We conclude that the device can potentially reduce the risk of musculoskeletal injuries and muscle fatigue associated with carrying heavy backpack loads while reducing the metabolic cost of loaded walking.

Multi-objective analysis for assessing simultaneous changes in regional spinal curvatures under backpack carriage in young adults

Change in sagittal spinal curvature from the neutral upright stance is an important measure of the heaviness and correctness of backpack use. As current recommendations, with respect to spinal profile, of backpack load thresholds were based on the significant curvature change in individual spinal region only, this study investigated the most critical backpack load by assessing simultaneously the spinal curvature changes along the whole spine. A motion analysis system was used to measure the curvature changes in cervical, upper thoracic, lower thoracic and lumbar regions with backpack load at 0, 5, 10, 15 and 20% of body weight. A multi-objective goal programming model was adopted to determine the global critical load of maximum curvature change of the whole spine in accordance with the maximum curvature changes of the four spinal regions. Results suggested that the most critical backpack load was 13% of body weight for healthy male college students. Practitioner Summary: As current recommendations of backpack load thresholds were based on the significant curvature change in individual spinal region only, this study investigated the backpack load by considering simultaneously the spinal curvature changes along the whole spine. The recommendation, in terms of the global critical load, was 13% of body weight for healthy male college students.

Analyzing the potential benefits of using a backpack with non-flexible straps

BACKGROUND

Conventional backpack straps are flexible. Due to this flexibility, backpacks freely move on the human back. In this study, a new design of backpacks with non-flexible straps is proposed.

OBJECTIVE

The aim of the present research is to demonstrate the possible differences between normal gait and steps while participants carry two different backpacks.

METHODS

In this investigation, 9 healthy male college students were recruited with mean age, height and weight of 24.6 years, 179.6 cm and 76.41 kg, respectively. Each backpack was tested in two different steps. First, the participants were asked to walk on a treadmill, whose velocity was changed from 1.5 m/s to 2.5 m/s, for 15 minutes. Initial velocity was 1.5 m/s and the velocity increased 0.5 m/s in 5 minutes increments. In the next step, they walked for 15 minutes with constant velocity of 3 m/s. Head, neck, and trunk flexion or extension, lateral displacement, and velocity of the subjects during backpack carriage were compared with the obtained values during normal gait, when they walked without carrying a backpack. In addition, the level of discomfort (3 grades: Low, medium, severe) in the neck, shoulder, lumbar, upper and lower leg muscles were investigated by using a modified standardized questionnaire.

RESULTS

By wearing the modified design of backpack, trunk flexion decreased while there was no significant (p > 0.05) change in velocity and lateral displacement. According to the questionnaire reports, more than 80% of the participants believed that both backpack discomfort in the neck (anterior side) and upper and lower legs were low. More than 75% of the subjects believed that by using a modified backpack, discomfort decreased for muscles in the neck (posterior), shoulder (posterior) and lumbar muscles. About 60% of both backpack users reported low discomfort in anterior shoulder muscles.

CONCLUSION

Backpacks cause some bad effects on kinematics of gait. In this study, by testing modified backpacks, some improvements were seen, specifically in posture, which may be useful to reduce side effects of backpack carrying.

Use of a backpack alters gait initiation of high school students

We assessed how backpack carriage influences the gait initiation (GI) process in high school students, who extensively use backpacks. GI involves different dynamics from gait itself, while the excessive use of backpacks can result in adverse effects. 117 high school students were evaluated in three experimental conditions: no backpack (NB), bilateral backpack (BB), and unilateral backpack (UB). Two force plates were used to acquire ground reaction forces (GRFs) and moments for each foot separately. Center of pressure (COP) scalar variables were extracted, and statistical parametric mapping analysis was performed over the entire COP/GRFs time series. GI anticipatory postural adjustments (APAs) were reduced and were faster in backpack conditions; medial-lateral COP excursion was smaller in this phase. The uneven distribution of the extra load in the UB condition led to a larger medial-lateral COP shift in the support-foot unloading phase, with a corresponding vertical GRF change that suggests a more pronounced unloading swing foot/loading support foot mechanism. The anterior-posterior GRFs were altered, but the COP was not. A possible explanation for these results may be the forward trunk lean and the center of mass proximity of the base of support boundary, which induced smaller and faster APA, increased swing foot/support foot weight transfer, and increased load transfer to the first step.

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.

Postural education program for elementary school: a one-year follow-up study

AbstractThe objective of this study was to verify the short- and long-term effectiveness of the Elementary School Postural Program in the performance, generalization, and perception of daily school activities. The final sample consisted of 61 subjects divided into experimental (14 years ±0.93; ♀=22; ♂=10) and control group (15.38 years ±0.97; ♀=16; ♂=13), all participants attended a Brazilian public school in Porto Alegre, State of Rio Grande do Sul. The postural program included 20 sessions over a 10-week period. In each session, participants discussed and practiced routine actions that typically occurred at schools. Eight other meetings were required for the completion of the pre- and post-tests. The experimental group performed significantly better than the control group in the short-term evaluations, although there were no significant statistical differences in the long-term follow-up evaluations. The children demonstrated a good behavioral response to the postural program; nevertheless, the knowledge had not been completely mastered after a year.

The effect of increase in baggage weight on elderly women's lower extremity muscle activation during gait

The aim of the present study was to examine the effect of increased baggage weight on the muscle activation of elderly women's lower extremities during gait. A total of 24 elderly women who were residing in communities in Daegu, South Korea aged 79.6±6.2, 149.7±7.0cm in height, and 53.5±7.2kg in weight participated in this study. The muscle activation of each muscle was measured three times at 2kg, 3kg, and 4kg of baggage weight while the subjects were conducting treadmill walking wearing backpacks. Electrodes were placed on four muscles: the quadriceps muscle (rectus femoris), the hamstring muscle (semitendinosus), the tibialis anterior muscle, and the soleus muscle. The results show that the rates of increase in muscle activation in the tibialis anterior and soleus muscles according to baggage weight increase were higher than those in the quadriceps and hamstring muscles (<0.05). These results indicate that the heavier weight loads increase the activation of muscles that control the ankle joints causing muscle fatigue. Moreover, a decrease in balance ability through muscle fatigue can be a risk factor for falls. Thus, elderly people should be instructed not to carry heavy objects.

The Effects on Muscle Activation of Flatfoot during Gait According to the Velocity on an Ascending Slope

[Purpose] This study determined the difference between flatfeet and normal feet in humans on an ascending slope using electromyography (EMG). [Subjects] This study was conducted on 30 adults having normal feet (n=15) and flatfeet (n=15), all of whom were 21 to 30 years old. [Methods] A treadmill (AC5000M, SCIFIT,) was used to analyze kinematic features during gait. These features were analyzed at slow, normal, and fast gait velocities on an ascending slope. A surface electromyogram (TeleMyo 2400T, Noraxon Co., USA) was used to measure muscle activity changes. [Results] The activities of most muscles in the subjects with flatfeet were significantly different from the muscle activities in the subjects with normal feet at different gait velocities on an ascending slope. There were significant differences in the vastus medialis and abductor hallucis muscles. [Conclusion] Because muscle activation of the vastus medialis in relation to stability of the lower extremity has a tendency to increase with an increase in gait velocity on an ascending slope, we hypothesized that higher impact transfer to the knee joints occurs in subjects with flatfeet due to the lack of a medial longitudinal arch and that the abductor halluces muscles, which provide dynamic stability to the medial longitudinal arches, do not activate well when they are needed in subjects with flatfeet.

Effect of backpack load on the head, cervical spine and shoulder postures in children during gait termination

Twelve boys with an average age of 9.9 years were instructed to carry backpacks that weighed 0%, 10% and 15% of their body weights (BWs) to complete planned and unplanned gait termination experiments. The craniohorizontal, craniovertebral and sagittal shoulder posture angles at the sagittal plane as well as the anterior head alignment and coronal shoulder posture angles at the coronal plane were analysed. Results revealed significantly smaller craniohorizontal and sagittal shoulder posture angles during planned gait termination and a significantly smaller sagittal shoulder posture angle during unplanned gait termination under loaded conditions compared with those at 0% BW backpacks. Furthermore, the coronal shoulder posture angles at 10% and 15% BW during planned and unplanned gait terminations were significantly larger than those at 0% BW. Therefore, subjects were more likely to have a forward head posture, rounded shoulder posture and increased lateral tilting of the shoulders during gait termination as backpack loads were increased. However, gait termination, whether planned or unplanned, did not elicit a remarkable effect on posture.

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.

Relative weights of the backpacks of elementary-aged children

The purpose of the study was to describe the range of relative backpack weights of one group of elementary-aged children and the extent to which they exceeded recommended levels. A second purpose was to explore whether gender and age help predict the relative weight of children's backpacks. Ninety-five 8- to 12-year-old elementary school students (56% girls; 88% car or bus riders) participated. Their school backpacks were weighed, and their age, gender, and mode of transportation to school were recorded. Only 40% of the sample carried backpacks that were less than 10% of their body weights. Five percent of the students' backpacks exceeded 20% of their body weights. Neither age group nor gender significantly predicted relative backpack weight or relative weight levels. Recommendations are made for ways to reduce the weight these young children carry.

Awareness of Parents about Characteristics of a Healthy School Backpack

BACKGROUND

The issue of knowledge on school backpacks among parents has received little attention. The objectives of this study were to assess school backpack carriage and its consistency with parents' knowledge about children friendly school backpacks.

METHODS

This was a randomized cross-sectional study. Totally 307 elementary school children and 250 parents were recruited to assess parental knowledge about standard school backpacks in 2010. Data collection were carried out on an unscheduled day in order to, children and their par¬ents prepared school backpacks based on their own previous habits and behaviors. All statistical analyses were performed using version 16.0 of the statistical software package SPSS Results: Approximately, 132 (51.6%) of the parents were not aware of the recommended weight limit for carrying school backpacks and 144 (56.3%) were not aware that the size of the backpack must be proportionate to the upper back region. Significant difference was found for the mean score of awareness of a safe and standard school backpack between fathers and mothers: fathers had more knowledge about school backpack carriages in comparison with mothers (P<0.001).

CONCLUSION

Children, parents and teachers should be educated about the characteristics of a standard backpack, different strategies. Parents are the best advocates for safety promotion and should represent the group most likely to help to significantly reduce backpack related injuries among school children by selecting safe school backpacks, supervising school backpack carrying and checking backpack weights.

The effect of school bag design and load on spinal posture during stair use by children

Thirteen male children ascending and descending stairs with loads that equalled 0%, 10%, 15% and 20% of their body weight were the subject of our research: the boys were wearing an asymmetrical single-strap athletic bag or a symmetrical double-strap backpack during our experiments with them. The maximum spinal tilt to the loading side and to the support side, and the range of spinal motions, were obtained by using a motion analysis system. Our results showed that symmetry of spinal posture was observed both when they ascended staircase with all loads and descended in a backpack. When carrying an athletic bag with 15% and 20% of their body weight while ascending the staircase, the lateral spinal tilt to the supporting side was significantly increased. We concluded that a symmetrical backpack with a load not exceeding 20% or an asymmetrical single-strap athletic bag with a load not exceeding 10% should be recommended for school children in order to promote safer staircase use. STATEMENT OF RELEVANCE: Children carrying heavy school bags may develop spinal problems. This study suggested that when they are using stairs, a symmetrical backpack with a load within 20% body weight is acceptable for them. When they are carrying an asymmetrical single-strap athletic bag, the bag's weight should not exceed 10% of the body weight in order to avoid excessive spinal tilt.

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.