Hip Belt Research Articles

The effect of hip belt use and load placement in a backpack on postural stability and perceived exertion: a within-subjects trial

The purpose of this study was to assess the effects of hip belt use and load placement in a backpack on perceived exertion and postural stability. Thirty participants were instructed to stand on a force plate and walk along a designated route under five conditions: unloaded, high-load placement, low-load placement, hip belt on and hip belt off. The average velocity and sway area from the force plate were measured. Participants also rated their perceived stability and exertion. Compared to the unloaded condition, all loaded conditions significantly increased average velocity, sway area, perceived stability and exertion. Hip belt use did not affect average velocity and sway area; however, participants reported higher levels of stability and lower levels of exertion with hip belt use. Load placement did not affect average velocity, sway area, perceived stability or exertion. This study showed that wearing a backpack loaded to 20% of body weight reduced postural stability, while manipulation of load placement in a backpack did not affect subjective and objective measures of postural stability. Also, hip belt use only improved subjective measures of postural stability.

The Effect of Continuous Positive Airway Pressure on Stair-Climbing Performance in Severe COPD Patients

Stair climbing is associated with dynamic pulmonary hyperinflation and the development of severe dyspnea in patients with chronic obstructive pulmonary disease (COPD). This study aimed to assess whether (i) continuous positive airway pressure (CPAP) applied during stair climbing prevents dynamic hyperinflation and thereby reduces exercise-induced dyspnea in oxygen-dependent COPD-patients, and (ii) the CPAP-device and oxygen tank can be carried in a hip belt. In a randomised cross-over design, oxygen-dependent COPD patients performed two stair-climbing tests (44 steps): with supplemental oxygen only, then with the addition of CPAP (7 mbar). The oxygen tank and CPAP-device were carried in a hip belt during both trials.Eighteen COPD patients were included in the study. Although all patients could tolerate stair climbing with oxygen alone, 4 patients were unable to perform stair climbing while using CPAP. Fourteen COPD patients (mean FEV1 36 ± 14% pred.) completed the trial and were analyzed. The mean flow rate of supplemental oxygen was 3 ± 2 l/min during stair climbing. Lung hyperinflation, deoxygenation, hypoventilation, blood lactate production, dyspnea and the time needed to manage stair climbing were not improved by the application of CPAP (all p > 0.05). However, in comparison to climbing with oxygen alone, limb discomfort was reduced when oxygen was supplemented with CPAP (p = 0.008).In conclusion, very severe COPD patients are able to carry supporting devices such as oxygen tanks or CPAP-devices in a hip belt during stair climbing. However, the application of CPAP in addition to supplemental oxygen during stair climbing prevents neither exercise-induced dynamic hyperinflation, nor dyspnea.

Effects of physical guidance on short-term learning of walking on a narrow beam

Physical guidance is often used in rehabilitation when teaching patients to re-learn movements. However, the effects of guidance on motor learning of complex skills, such as walking balance, are not clear. We tested four groups of healthy subjects that practiced walking on a narrow (1.27 cm) or wide (2.5 cm) treadmill-mounted balance beam, with or without physical guidance. Assistance was given by springs attached to a hip belt that applied restoring forces towards beam center. Subjects were evaluated while walking unassisted before and after training by calculating the number of times subjects stepped off of the beam per minute of successful walking on the beam (Failures per Minute). Subjects in Unassisted groups had greater performance improvements in walking balance from pre to post compared to subjects in Assisted groups. During training, Unassisted groups had more Failures per Minute than Assisted groups. Performance improvements were smaller in Narrow Beam groups than in Wide Beam groups. The Unassisted-Wide and Assisted-Narrow groups had similar Failures per Minute during training, but the Unassisted-Wide group had much greater performance gains after training. These results suggest that physical assistance can hinder motor learning of walking balance, assistance appears less detrimental for more difficult tasks, and task-specific dynamics are important to learning independent of error experience.

Electromyographic assessment of apple bucket intervention designed to reduce back strain

The authors previously developed an apple bucket that was modified by use of a hip belt to reduce muscle fatigue. The intervention of belt use was accepted by workers and shown not to interfere with productivity. However, use of this intervention did not appear to reduce muscle fatigue when measured by tests of voluntary muscle strength. The purpose of the present study was to evaluate the intervention's effect on muscle fatigue employing surface electromyographic (EMG) amplitude. Amplitude measurements on 15 muscles were taken from 10 laboratory volunteers who were carrying a full bucket of apples, once while wearing the intervention belt and once without the intervention. These measurements were taken for seven different postures (four angles of trunk flexion (0°, 20°, 45°, 90°) and three raised-arm positions (both up, dominant up, non-dominant up)) common to apple harvest work. Participants were measured in these conditions both with the bucket carried in front and with the bucket carried to the side. Significant reductions in amplitude favouring the intervention were seen for 11 of the 15 muscles in models considering the four body flexion angles. Ten of these were of the middle and lower back. These control/intervention differences were seen with both bucket-carrying positions (front vs. side) and tended to increase with increasing flexion angle. In contrast, no significant intervention effects were observed in models considering treatment by arm-raised position. One significant main effect (upper trapezius, side bucket) showed an amplitude reduction in the treatment condition. Another main effect showing increased amplitude in the intervention condition use was observed in the dominant levator scapulae (side bucket). Thus, the use of the intervention belt reduces EMG amplitude among a number of mid- and lower-back muscles. This is suggestive of a protective effect against back strain.

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

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

Orchard Evaluation of Ergonomically Modified Apple Bucket

Background: While preliminary laboratory tests indicate that a hip belt reduces the load on the back, neck and shoulders associated with musculoskeletal strain, an orchard trial is needed to more realistically assess both effectiveness and acceptability. Objective: to evaluate the hip belt's effectiveness in three areas: worker acceptance, worker productivity, and one-day muscle fatigue of the back and shoulder. Methods: Ninety-six New York apple harvest workers were randomly assigned to use the intervention hip belt or placebo belt for one week. In a second week all workers switched conditions. Subjects were interviewed at the end of each week to ascertain intervention acceptance. Employer records were reviewed to determine bushels picked per day. Subjects also underwent muscle fatigue testing at the beginning and again at the end of one workday during each week. Results: Ninety-one percent of the subjects favored the intervention hip belt. Use of the intervention did not appreciably slow picking speed (bushels per hour) as compared to placebo (8.8 bu/ hr vs. 8.89 bu/hr). Both were significantly faster than the regular equipment condition (8.13 bu/hr). No significant differences in one-day muscle fatigue were found with intervention use. Conclusions: The belt was acceptable to the workers and did not hinder productivity. However, the anticipated ergonomic benefits were not demonstrable using one-day strength testing.

Essay: Wilderness medicine and creativity

Essay: Wilderness medicine and creativity

An evaluation of backpack harness systems in non-neutral torso postures

Much of the research on backpack design has been focused on spinal loading/biomechanics while the wearer is in a neutral/upright trunk posture, such as those employed by outdoor enthusiasts and schoolchildren. This research has led to some important harness design improvements that reduce trunk muscle exertions, fatigue and improve overall comfort. There are number of occupations, however, wherein workers wear back-mounted packs/devices (e.g. air tanks) while working in non-neutral trunk postures. The objective of the current study was to evaluate the effects of these non-neutral postures on biomechanical loading and then reconsider the backpack system design recommendations. Fifteen participants were asked to support a 18.2 kg load on their back while assuming static forward flexed postures of the torso (15°, 30°, 45°, and 60° of sagittal bend). The mass on the back was attached to the participant through two different harness mechanisms: a basic harness design (as seen on college student backpacks) and a more advanced design containing lateral stiffness rods and a weight-bearing hip belt (as seen on backpacks for hikers). While performing these static, posture maintenance tasks, the activation levels of the bilateral trapezius, erector spinae, and rectus abdominis were collected. Participants also provided subjective ratings of comfort. The results showed that there was a significant interaction between harness type and forward flexion angle for the trapezius and the erector spinae muscles. The normalized EMG for the trapezius muscles showed a 14% and 11% reduction in muscle activity at 15° and 30°, respectively, with the advanced design but these positive effects of the advanced design were not found at the greater flexion angles. Likewise the erector spinae muscles showed a 24% and 14% reduction in muscle activity at 15° and 30°, respectively, with the advanced design harness but these effects of the advanced design were not found at the greater forward flexion angles. The level of forward flexion angle affected the rectus abdominis muscle activity, but neither the harness type main effect nor the interaction of harness type and forward flexion angle was significant. The subjective survey results agreed with the EMG results and showed the advanced design harness was generally more comfortable with respect to the shoulder and low back areas. Collectively, the subjective and objective results show a significant improvement with the advanced harness system but also note an interesting interaction with degree of sagittal flexion, indicating a diminished effectiveness of the design improvements at forward flexed postures. Design criteria for harness systems in these forward flexed postures are discussed.

Effect of belt/bucket interface in apple harvesting

Migrant and seasonal orchard harvest workers experience musculoskeletal strain caused by carrying heavily loaded buckets and holding awkward postures. An ergonomic hip belt has been shown (both in this and previous studies) to significantly assist in redistributing weight from the shoulders to the hips. Two types of belt/bucket interfaces were tested: A hook belt with hooks on the buckets attaching to prepositioned D rings or a cable belt with hooks sliding a cable attached to the belt. A laboratory study of simulated harvesting postures showed significantly ( p<0.001) reduced loading on the shoulder strap and greater transfer of the load to the hips using the cable belt. This was confirmed with significantly ( p<0.05) reduced subjective ratings of shoulder discomfort for the cable belt as compared to the hook belt. Field testing with apple harvesters showed similar but nonsignificant results. This effect is hypothesized to be due to the cable belts more uniform distribution of load and greater flexibility in adjusting the position of the bucket on the belt. Relevance to industry Improved belt/bucket interfaces have the potential for significantly reducing back and shoulder strain in apple harvesters.

Laboratory evaluation of belt usage with apple buckets

Migrant and seasonal orchard harvest workers experience musculoskeletal strain caused by carrying heavy loads and holding awkward postures. An ergonomic hip belt designed to redistribute weight from the upper back, neck, and shoulders to the hips was evaluated. A comparison of muscle exertion (using electromyography [EMG]) of four key back and shoulder muscles and shoulder surface pressure (using a surface pressure sensor [PS]) was made among 10 laboratory volunteers under intervention and control conditions, in two postures (standing erect [0 degrees ]) and flexed [45 degrees ]). All but one measure showed a significant reduction in the flexed posture with the intervention. Two of eight measures showed a significant reduction in the erect posture. Correlations with shoulder discomfort were found for deep shoulder EMG (r=0.71, P=0.021) and shoulder surface pressure (r=0.58, P=0.082). The hip belt intervention produces significant reductions in muscle activity while in a posture commonly assumed during orchard work.

An ergonomic intervention to reduce back strain among apple harvest workers in New York State

The impact of modifications to the apple picking bucket on common picking postures, self-reported comfort, ease of use, and speed of harvest were measured. Fourteen apple pickers wore an intervention hip belt, were interviewed and measured using posture-activities-tools-handling methodology. The use of hip belt did not significantly alter time spent in various postures. 78.6% of interviewed workers preferred the modified bag, 71.4% noted a difference in the back, neck, or shoulder, while 64.3% said regular use of modified bag would slow their work. Major themes in worker comments are discussed. The hip belt modification to apple harvest bag seems generally acceptable to workers, but needs further development to overcome unintended effects. Although work sampling demonstrates that the bag does not affect work practices, workers appear somewhat concerned that productivity will be negatively impacted. Further training of workers in the use and potential benefits of bag are needed.

Women's Load Carriage Performance Using Modular Lightweight Load-Carrying Equipment

The purposes of this study were to evaluate how Modular Lightweight Load-Carrying Equipment (MOLLE) fits women while walking on level surfaces with different loads, to examine women's load carriage performance before and after a simulated march using five load levels, and to examine the relationship between shoulder and leg muscle strength and load carriage performance of women while carrying loads using MOLLE. Seven physically active women carried five levels of load (no load, 20, 30, 40, and 50 pounds) using MOLLE. With increased loads, women showed increased double-limb support time, decreased single-limb support time, increased trunk forward inclination excursion, decreased knee excursion, decreased medial-lateral excursion of center of gravity (COG), and increased vertical excursion of COG. Hip abductor strength was a strong predictor of COG vertical excursion. Some women required modification of the padded hip belt to ensure weight distributed evenly around the pelvis.

Biomechanical assessment of lateral stiffness elements in the suspension system of a backpack

The purpose of this study was to examine the change in load distribution characteristics associated with adding lateral stiffness elements (rods) to a rucksack (backpack). A load distribution mannequin was instrumented with two 3D load cells to allow determination of the load applied to the shoulders and upper torso independent of the load applied to the hips and lower trunk. Position and mass of the payload (25 kg) were fixed at the centre of the volume of the rucksack and held constant during all testing. It was hypothesized that lateral rods would provide a force bridge that transfers part of the vertical load of the pack from the upper back and shoulders to the hip belt thereby reducing the vertical load on the torso, and possibly reducing the horizontal reaction force that produces a shear load on the spine. Results showed that these active stiffness elements shifted 14% of the vertical load from the upper torso to the pelvic region with lumbar shear load remaining relatively unchanged for all combinations of shoulder strap and waist belt tension. The lateral rods also provided a mean increase of 12% in the extensor moment at the L3 – L4 level, thus reducing some demand on the erector spinae muscles.

The Distribution of Forces between the Upper and Lower Back during Load Carriage

To determine the effects of backpack mass on the forces exerted by the backpack on the carrier and on the distribution of these forces between the upper back (including shoulders) and lower back (sacrum and iliac crest). Eleven male volunteers (mean age 22.7 SEM 1.1 yr) walked on a level treadmill at 1.34 m.s(-1) carrying a backpack loaded to three different masses (13.6, 27.2, and 40.8 kg). The backpack's hip belt was connected to force transducers that measured the forces exerted on the lower back. The total force between the subject and backpack was determined from the backpack's mass and acceleration. Forces on the upper back were calculated as total force minus the forces exerted on the lower back. There was a significant effect of backpack mass on the vertical and anterior/posterior forces exerted on the upper and lower back, and on the total force exerted on the backpack center of mass. Regardless of mass, approximately 30% of the vertical force was borne by the lower back; the upper back and shoulders supported the remaining 70%; this is based on data averaged across the stride. Dimensionless analysis revealed peak forces on the upper and lower back increased proportionately to backpack mass whereas the peak forces exerted on the backpack COM increased disproportionately. The backpack exerts consistent anterior force on the lower back, which likely contributes to the occurrence of low-back pain associated with load carriage. Approximately 30% of the vertical force generated by the backpack can be transferred to the lower back by using an external frame backpack with a hip belt.

Effect of backpack fit on lung function

Carrying loads close to the trunk with a backpack causes a restrictive type of change in lung function in which Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 s (FEV1) are reduced without a corresponding decrement in the FEV1.FVC − 1 %. It is not known whether this is due to the weight of the load acting on the chest or to the tightness of fit of the shoulder and chest straps and waist belt of the pack harness. This study examined FVC, FEV1, FEV1.FVC − 1 %, peak expiratory flow (PEF), forced expiratory flow between 0.2 and 1.2 s (FEF0.2 – 1.2) after the start of expiration and between 25 and 75% of each FVC (FEF25 – 75%) in 12 healthy males wearing a 15 kg backpack in which the shoulder and chest straps and hip belt were loosened by 3 cm from a ‘comfort fit’ to achieve a ‘loose pack’ fit (LPF) and tightened by 3 cm from CF to achieve a ‘tight pack’ fit (TPF). In comparison with the control condition of no pack, a loose pack fit significantly reduced FVC (by 3.6%, p < 0.01), FEV1 (by 4.3%, p < 0.01) and FEF25 – 75% (by 8.4%, p < 0.01). A tight pack fit significantly reduced FVC (by 8.1%, p < 0.01) and FEV1 (by 9.1%, p < 0.001). It also significantly reduced FEF0.2 – 1.2 (by 7.3%, p < 0.05) and FEF25 – 75% (by 21%, p < 0.01). In comparison with a loose pack fit, the tight pack fit was associated with a significantly lower FVC (by 4.6%, p < 0.01), FEV1 (by 5.0%, p < 0.01), FEF25 – 75% (by 13.8%, p < 0.01) and a fall in FEF0.2 – 1.2 (by 5.5%). The latter was approaching significance (p = 0.077). There were no significant changes in FEV1.FVC − 1% and PEF. It is concluded that tightening the fit of a backpack significantly affects lung function in a manner that is typical of a restrictive change in lung function and is very similar in pattern to that of wearing a loosely fitted loaded backpack. The effect of tightness of fit is additional to that due to the weight of the load alone and may also reduce expiratory flow at low lung volumes.