Carry-over effects of backpack carriage on trunk posture and repositioning ability

Immediate effects of backpack carriage on spinal curvature and motor control in adults have been reported. However, there is a scarcity of evidence whether the effects would persist or not after the carrying load is removed. This study aimed to investigate the carry-over effects of backpack carriage on trunk posture and repositioning ability. Thirteen healthy adults were recruited and instructed to walk on a treadmill for 30 min with backpack (10% body weight) followed by 30-min unloaded walking. Participant’s trunk posture and repositioning ability were measured at different time points. During backpack carriage, reduction in lumbar lordosis and posterior pelvic tilt with significant increased cervical lordosis, thoracic kyphosis and trunk forward lean were observed. There was also a significant increase in repositioning errors in all spinal curvatures and trunk forward lean. After removal of the carrying load, there was a tendency for restoration of trunk posture and repositioning ability. However, the cervical lordosis and the repositioning error of all spinal curvatures could not be fully returned to the levels of the preload condition (all p < 0.05). The persistent changes in both spinal curvature and repositioning ability revealed an increased risk of spinal injury even after the backpack was removed, and the effects on the neck and back pain warrant future study.

Relevance to Industry

The effects of backpack carriage (10% body weight for 30 min) on the spine could not be fully restored after 30-min unloaded walking. The persistent changes in both spinal curvature and repositioning ability revealed an increased risk of spinal injury even after the backpack was removed. Proper postural reminder might be given to backpack users to alleviate the adverse effects induced after prolonged backpack carriage.     

Effects of backpack load placement on pulmonary capacities of normal schoolchildren during upright stance

Backpack carriage affects posture, physiological costs and physical performance. Limited literature concerning the effects of backpack load placement on pulmonary capacities of schoolchildren has been reported. The objective was to assess the effects of backpack load placement on pulmonary capacities of normal schoolchildren. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), peak expiratory flow (PEF), and forced expiratory flow (FEF_25–75%) were measured in 22 normal schoolchildren with a mean age of 12 years during free standing and when carrying a backpack of 15% bodyweight with its center of gravity positioned at T7, T12 and L3. The main effect of load was found to be significant for FVC and FEV₁. However, no significant effect of load placements on the pulmonary function of schoolchildren was found. Manipulation of load placements may not alleviate the restrictive effects exerted on the pulmonary function resulted from backpack load carriage.

Relevance to industry

Daily carriage of a school backpack on the musculoskeletal health of children and adolescents has become an area of concern. Restrictive effects on the pulmonary function due to backpack carriage were reported and it is useful to explore whether these effects could be alleviated by manipulating the backpack center of gravity level.     

Changes in spinal curvature and proprioception of schoolboys carrying different weights of backpack

Despite evidence linking backpack carriage and back pain, previous studies to examine the effects of backpack carriage have focused on changes in physical performance rather than the direct effects on the spine itself. Spinal curvature and proprioception (in terms of spinal repositioning consistency) of 15 schoolboys during normal upright stance without a backpack and while carrying a specially adapted backpack loaded at 10, 15 and 20% of their bodyweight were measured and compared using repeated measures ANOVA. A significant flattening of the lumbar lordosis and the upper thoracic kyphosis was found with increasing backpack load, as well as a significant decrease in the thoraco-lumbar and lumbar repositioning consistencies. Carriage of a loaded backpack causes immediate changes in spinal curvature and appears to have a direct effect on the repositioning consistency. Further investigation of the changes in spinal curvature and repositioning consistency over time with prolonged backpack carriage is warranted. Daily carriage of a school backpack on the musculoskeletal health of children and adolescents has become an area of concern due to the association between backpack carriage and back pain. Data regarding the direct effect of backpack carriage on the spine in children are limited.     

Changes in spinal curvature and proprioception of schoolboys carrying different weights of backpack

Despite evidence linking backpack carriage and back pain, previous studies to examine the effects of backpack carriage have focused on changes in physical performance rather than the direct effects on the spine itself. Spinal curvature and proprioception (in terms of spinal repositioning consistency) of 15 schoolboys during normal upright stance without a backpack and while carrying a specially adapted backpack loaded at 10, 15 and 20% of their bodyweight were measured and compared using repeated measures ANOVA. A significant flattening of the lumbar lordosis and the upper thoracic kyphosis was found with increasing backpack load, as well as a significant decrease in the thoraco-lumbar and lumbar repositioning consistencies. Carriage of a loaded backpack causes immediate changes in spinal curvature and appears to have a direct effect on the repositioning consistency. Further investigation of the changes in spinal curvature and repositioning consistency over time with prolonged backpack carriage is warranted. Daily carriage of a school backpack on the musculoskeletal health of children and adolescents has become an area of concern due to the association between backpack carriage and back pain. Data regarding the direct effect of backpack carriage on the spine in children are limited.     

Effect of load carriage on spinal compression

Backpack is commonly carried either posteriorly or anteriorly. Although load carriage has been shown to have significant effects on postural alignment and spinal muscle activity, its effect on spinal loading was not studied. The objective of this study is to investigate the effect of different load carriage methods on spinal loading over time via the measurement of spinal compression. Eight male adults participated in this study. They were asked to carry a load equivalent to 15% of their body weight either anteriorly or posteriorly for 20 min followed by 10 min of unloading. Their statures were measured before load carriage and every 2 min after carrying the load. The sequence of loading conditions was randomized and the participants took a 20-min rest with Fowler’s posture for spinal length recovery prior to each testing condition. The amount of spinal compression was found to be associated with carrying duration. Spinal compression during anterior carriage was larger than that of posterior carriage. There was a mild recovery of spinal compression after the removal of the carried load for both the anterior and posterior carriage conditions.

Relevance to industry

Short-term putting a backpack anteriorly might be useful for temporarily relieving postural changes induced by posterior carriage. However, prolonged anterior carriage is not recommended. The effects of load carriage on spinal compression should be considered in the design of a load carriage system with load partially or completely positioned in the front     

Effects of backpack carriage on lumbopelvic control: A dynamical systems analysis

Although heavy backpack carriage has been associated with back pain in schoolchildren, its causal relationship is still unknown. As people with low back pain exhibit an abnormal spinal control and backpack carriage has been shown to affect spinal repositioning ability in static upright stance, the goal of this study is to use dynamical systems theory to investigate the effects of backpack carriage on lumbopelvic control under dynamic situation. Lumbopelvic coordination was quantified in terms of Mean Absolute Relative Phase (MARP) and Deviation Phase (DP) whilst performing a reaching task under four loading conditions, i.e. no load, carrying 5%, 10% and 15% bodyweight (BW). It was shown that inter-segmental coordination was less in-phase (i.e. significant reduction in MARP with p < 0.001) and more variable (i.e. significant increase in DP with p = 0.005) during backpack carriage of 10% and 15% BW in forward reaching movement, suggesting greater alteration in lumbopelvic coordination at heavier weights. As abnormal movement strategies tend to increase the risk of spinal injury, pragmatic approaches should be considered to eradicate the adverse effect of heavy backpack carriage on spinal proprioception.     

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.     

The effect of load distribution within military load carriage systems on the kinetics of human gait

Military personnel carry their equipment in load carriage systems (LCS) which consists of webbing and a Bergen (aka backpack). In scientific terms it is most efficient to carry load as close to the body's centre of mass (CoM) as possible, this has been shown extensively with physiological studies. However, less is known regarding the kinetic effects of load distribution. Twelve experienced load carriers carried four different loads (8, 16, 24 and 32 kg) in three LCS (backpack, standard and AirMesh). The three LCS represented a gradual shift to a more even load distribution around the CoM. Results from the study suggest that shifting the CoM posteriorly by carrying load solely in a backpack significantly reduced the force produced at toe-off, whilst also decreasing stance time at the heavier loads. Conversely, distributing load evenly on the trunk significantly decreased the maximum braking force by 10%. No other interactions between LCS and kinetic parameters were observed. Despite this important findings were established, in particular the effect of heavy load carriage on maximum braking force. Although the total load carried is the major cause of changes to gait patterns, the scientific testing of, and development of, future LCS can modify these risks.     

Effects of backpack load and positioning on nonlinear gait features in young adults

Overloaded backpacks can cause changes in posture and gait dynamic balance. Therefore, the aim of this study was to assess gait regularity and local dynamic stability in young adults as they carried a backpack in different positions, and with different loads. Twenty-one healthy young adults participated in the study, carrying a backpack that was loaded with 10 and 20% of their body weight (BW). The participants walked on a level treadmill at their preferred walking speeds for 4 min under different conditions of backpack load and position (i.e. with backpack positioned back bilaterally, back unilaterally, frontally or without a backpack). Results indicate that backpack load and positioning significantly influence gait stability and regularity, with the exception of the 10% BW bilateral back position. Therefore, the recommended safe load for school-age children and adolescents (10% of BW) should also be considered for young adults.

Practitioner summary: Increase in load results in changes in posture, muscle activity and gait parameters, so we investigated the gait adaptations related to regularity and stability. Conditions with high backpack loads significantly influenced gait stability and regularity in a position-dependent manner, except for 10% body weight bilateral back position.     

The effect of backpack load on the gait of normal adolescent girls

Concerns regarding the effects of load carriage have led to recommendations that backpacks be limited to 10?–?15% of body weight, based on significant changes in physical performance. However, gait responses to backpack loads are not entirely consistent and there is a particular lack of data regarding load-bearing gait in adolescent females. Gait patterns of 22 normal adolescent girls were recorded at backpack loads of 0, 7.5, 10.0, 12.5 and 15.0% body weight. Temporal-distance, ground reaction force and joint kinematic, moment and power parameters were analysed by repeated measures ANOVA with factors of backpack load and side (left or right).

Walking speed and cadence decreased significantly with increasing backpack load, while double support time increased. Kinematic changes were most marked at the proximal joints, with a decreased pelvic motion but a significant increase in the hip sagittal plane motion. Increased moments and power at the hip, knee and ankle showed increasing demand with backpack load. Parameters showed different responses to increasing load, and those that suggested a critical load indicated this to be approximately 10% body weight. While this may be due to a change in gait due to increased demand, further work is required to verify this and also to examine the cumulative effects of backpack load on the musculoskeletal system, which may be more appropriate in determining recommended load limits.     

The effect of backpack load on the gait of normal adolescent girls

Concerns regarding the effects of load carriage have led to recommendations that backpacks be limited to 10?-?15% of body weight, based on significant changes in physical performance. However, gait responses to backpack loads are not entirely consistent and there is a particular lack of data regarding load-bearing gait in adolescent females. Gait patterns of 22 normal adolescent girls were recorded at backpack loads of 0, 7.5, 10.0, 12.5 and 15.0% body weight. Temporal-distance, ground reaction force and joint kinematic, moment and power parameters were analysed by repeated measures ANOVA with factors of backpack load and side (left or right). Walking speed and cadence decreased significantly with increasing backpack load, while double support time increased. Kinematic changes were most marked at the proximal joints, with a decreased pelvic motion but a significant increase in the hip sagittal plane motion. Increased moments and power at the hip, knee and ankle showed increasing demand with backpack load. Parameters showed different responses to increasing load, and those that suggested a critical load indicated this to be approximately 10% body weight. While this may be due to a change in gait due to increased demand, further work is required to verify this and also to examine the cumulative effects of backpack load on the musculoskeletal system, which may be more appropriate in determining recommended load limits.     

The effect of load mass and its placement on postural sway

The purpose of this study was to investigate the effects of increasing load on postural sway in two different carrying positions: backpack and waist jacket. Potential differences between males and females were additionally evaluated. 60 young college students participated in this study, and were assigned to backpack and waist jacket groups. The loads in both groups were 12, 21 and 30 kg. Stabilometry was used to assess the amount of postural sway. The medio-lateral and antero-posterior mean sway, mean velocity, medio-lateral and antero-posterior path length and sway area of the centre of pressure position were calculated.In the backpack group all analyzed sway parameters linearly increased with additional load, the differences were significant at p < 0.001. However no significant change of the analyzed parameters was found when the subjects carried additional load in the waist jacket.Our results indicate that postural sway depends on the amount of the load carried in a backpack. Additionally, the position of the load is of significant importance. Carrying weight in a backpack increases postural sway with increasing weight whereas carrying weight in a waist jacket does not influence the amount of postural sway. There are no significant differences in the response to the amount and configuration of the load between male and female subjects.     

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.     

The effect of wearing high-heels and carrying a backpack on trunk biomechanics

Carrying a bag while wearing high-heels during daily life could potentially cause back pain. No study has investigated the combined effects of wearing a backpack and high-heels on trunk biomechanics from a system-level interaction viewpoint. Consequently, this study aimed to investigate the effects of high-heel height, backpack weight, and habituation in high-heels use on upper body biomechanics. Sixteen female study participants, all in their 20s, were divided into high-heel USER and NON-USER groups, and asked to carry a backpack with 0%, 5% and 10% of their body weight while either not wearing or wearing (0 cm and 9 cm) high-heels. Trunk kinematics and muscle activations were measured under the neutral standing posture while gazing straight ahead in experimental trials. First, the USERS tended to show hyper-lumbar lordosis when wearing high-heels, but the NON-USERS experienced lumbar kyphosis. In line with this, the USERS showed significantly greater recruitment of back muscles (35.5%), but the NON-USERS tended to recruit significantly more abdominal muscles (80%) to control their posture. Second, carrying a backpack sequentially induced posterior pelvic tilting, lumbar kyphosis, and forward head posture which is a stereotype posture of the hyper-kyphotic back and which suggests a system-level interaction from the lower extremity to the head. Third, the backpack weight eliminated the effect of wearing high-heels in the lumbar flexion angle, which may act as a counterbalance to pull the center of gravity (CoG) posteriorly.Relevance to industryCaution must be taken in the long-term use of high-heels and a backpack. Carrying a backpack weighing about 5% of the body weight is recommended to counterbalance the hyper-lordotic lumbar posture when wearing high-heels if unavoidable.     

Load carriage using packs: a review of physiological, biomechanical and medical aspects

This paper reviews the biomedical aspects of transporting loads in packs and offers suggestions for improving load-carriage capability. Locating the load mass as close as possible to the body center of gravity appears to result in the lowest energy cost when carrying a pack. Thus, the double pack (half the load on the front of the body and half the load on the back) has a lower energy cost than the backpack. However, backpacks provide greater versatility in most situations. The energy cost of walking with backpack loads increases progressively with increases in load mass, body mass, walking speed or grade; type of terrain also influences energy cost. Predictive equations have been developed for estimating the energy cost of carrying loads during locomotion but these may not be accurate for prolonged (>2 h) or downhill carriage. Training with loads can result in greater energy efficiency since walking with backpack loads over several weeks decreases energy cost. Load-carriage speed can be increased with physical training that involves regular running and resistance training. Erector spinae electrical activity (EMG) is lower during load carriage than in unloaded walking until loads exceed 30-40 kg, at which point erector spinae EMG activity is higher than during unloaded walking. EMGs of the quadriceps and gastrocnemius, but not the tibialis anterior or hamstrings, increase with load. Framed packs with hip belts reduce the electrical activity of the trapezius muscles, presumably by shifting forces from the shoulders to the hips. Increases in the backpack load mass result in increases in forces exerted on the grounds, amount of knee flexion and the forward inclination of the trunk. Compared to backpacks, double packs produce fewer deviations from normal walking. Common injuries associated with prolonged load carriage include foot blisters, stress fractures, back strains, metatarsalgia (foot pain), rucksack palsy (shoulder traction injury) and knee pain. Closed-cell neoprene insoles and use of an acrylic or nylon sock, combined with a wool sock, reduce blister incidence. A framed pack with a hip belt reduces the incidence of rucksack palsy. Backpack load carriage can be facilitated by lightening loads, optimizing equipment, improving load distribution and by preventive action aimed at reducing the incidence of injury.     

Protocols used to determine the influence of backpack load on physiological variables. Systematic review

Professional mountain rescue mountain groups use backpack equipment in their professional activities. The velocity of ambulation, gradient, load and the participant's physical characteristics have been described in the scientific literature as influential factors on response to exercise. The purpose of the present systematic review is to assess the protocols used to investigate the effects of backpacks and their influence on physiological responses at laboratory. A total of 14 articles were included in the review. Most research studies indicated participants were not experienced with backpack carriage. We observed a certain threshold on physiological changes in response to exercise was between 20 and 40 kg of backpack load. In conclusion, there is a heterogeneity of protocols used at the laboratory, hampering the comparison between different results. Future research should focus on the design of protocols that reproduce real scenarios of targeted populations.Relevane to industryRescue groups, firefighters and military personnel carry load with backpack in emergency interventions. This review analyzes different types of methodological protocols that investigate the influence of backpack load on physiological responses during exercise. The result will help manufacturer design backpacks considering the physiological burden of backpack carriage.     

Effects of backpack load on critical changes of trunk muscle activation and lumbar spine loading during walking

This study investigated the effects of carrying a backpack while walking. Critical changes featuring the disproportionality of increases in trunk muscle activation and lumbar joint loading between light and heavy backpack carriage weight may reveal the load-bearing strategy (LBS) of the lumbar spine. This was investigated using an integrated system equipped with a motion analysis, a force platform and a wireless surface electromyography (EMG) system to measure the trunk muscle EMG amplitudes and lumbar joint component forces. A predictive goal programming model was developed to determine the most critical changes in trunk muscle activation and lumbar joint loading. Results suggested that lightweight backpack carriage at approximately 3% of body weight (BW) might reduce the peak lumbosacral compression force by 3% during walking compared with no load condition. The most critical changes in both trunk muscle activation and lumbosacral joint loading were found at a backpack load of 10% of BW.

Practitioner Summary: This study investigated the effects of backpack load on the LBS of lumbar spine while walking. A backpack load of 3% of BW might reduce the peak lumbosacral compression force by 3 and 10% of BW induced the most critical changes in LBS of lumbar spine.     

School backpack design: A systematic review and a summary of design items

The purpose of this paper is to systematically review the recent literatures to obtain a summary of significant items (see Table B1) for better student backpack design for health improvement, as well as to identify gaps for further research. A systematic review was performed in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), targeting papers of the last 20 years. Thirty-six studies were included, assessed and synthesised. Four categories of design-related items were summarised: Biomechanical consideration, Strap, Dimension and Carrying method. Quality assessments were completed for the included studies by utilising different tools. The major health outcomes associated with the design-related items were posture, perception, metabolic cost, lung function, contact pressure of foot or shoulder, and muscle activity. An optimal location for the centre of mass of a backpack could not be ascertained from this review in the aspect of spinal curvature and postural displacement, and there was usually no best input that induced the best outcome in every dimension. Oscillation in the medial-lateral direction should be minimised, and wider shoulder strap should be utilised, together with hip straps. Different carrying methods, such as double pack, BackTpack, modified backpack, and frontpack, were superior to the traditional backpack, whereas the single-strap pack should be avoided. Some gaps, such as lack of standardised protocol and evidence for clinical significance, were identified. Meanwhile, the risk of bias is commonly high for recent studies.     

Influence of school bag loads and carrying methods on body strain among young male students

This study examined the influences of schoolbag carrying modes combined with carrying weights on the body posture alterations, muscle activations, and subjective discomfort scores of participants. Twelve male university students were recruited as participants and executed nine test combinations of three carrying methods (2-strap backpack, 1-strap side backpack, and 1-strap crossbody carrying) generally used by Taiwanese young students and three loads (5%, 10%, and 15% of their respective body weights [BWs]). The results revealed that carried load and method significantly affected body posture and trapezius activation. Side backpack carrying should be avoided because of the relatively high lateral shoulder tilt, trunk flexion, right trapezius activation, and low lumbosacral angle observed compared with other two carrying methods. The unbalanced load of side backpack carrying may cause an uneven shoulder posture, thus resulting in extra body strains. Furthermore, carrying loads at 10% of BW was recommended when carrying a 2-strap backpack.Relevance to industryThe daily carriage of a schoolbag or backpack on the musculoskeletal health of young students has been a permanent concern. The findings suggest that carrying a load weighing 15% of BW and using the unbalanced side backpack carrying method should be avoided.     

How does a backrest work?

After discussing the distribution of forces in the stable upright posture and illustrating the importance of the lumbar lordosis for minimising muscular effort in this position, the loadings on the spine and muscles of the back are outlined during upright sitting. It is shown that the backrest locates the lumbar spine so that the CG of the superincumbent body parts can be positioned above the vertebrae, permitting the gravity load to be transmitted to the seat without the counteracting torques which muscles would have to provide if this position was not adopted. The forces arising from other sitting positions are then discussed, and some conclusions drawn for seat design.