Effects of load carriage on measures of postural sway in healthy, young adults: A systematic review and meta-analysis

Altered trunk-pelvis kinematics during load carriage with a compliant versus a rigid system

Load carriage is a key component of hiking and military activity. The design of the load carriage system (LCS) could influence performance and injury risk. This study aimed to compare a traditional and a compliant LCS during walking and a step-up task to quantify differences in oxygen consumption and trunk-pelvis kinematics. Fourteen participants completed the tasks whilst carrying 16 kg in a rigid and a compliant LCS. There were no differences in oxygen consumption between conditions during either task (p > 0.05). There was significantly greater trunk-pelvis axial rotation (p = 0.041) and lateral flexion (p = 0.001) range of motion when carrying the compliant LCS during walking, and significantly greater trunk-pelvis lateral flexion range of motion during the step-up task (p = 0.003). Carrying 16 kg in a compliant load carriage system results in greater lateral flexion range of motion than a traditional, rigid system, without influencing oxygen uptake.

Backpack loading position and self-selected foot position as measured by foot tracings

BACKGROUND

It is known that even under static conditions a backpack wearer will need to make some adjustments to maintain postural stability. There is a paucity of research exploring the impact of altering the position of the feet with imposed loads of variable distance from the posterior midline.

OBJECTIVE

Therefore, the aim of this study was to determine if changes in the horizontal position of a fixed load when wearing a backpack affect specific variables derived from foot tracings of males and females standing with their self-selected natural feet position.

METHODS

150 healthy volunteer participants were instructed to adopt a natural stance across four conditions: Backpack with no weight, backpack with a weight (5% of body mass) placed at 0 cm, 20 cm, and 40 cm distance from the posterior body. Foot tracings were made for each condition. Base of Support (BoS), Feet Width (FW), and Feet Opening Angle (FOA) were calculated.

RESULTS

The BoS significantly decreased in loaded conditions (0 cm, 20 cm and 40 cm) compared to unloaded. This was supported by FW and FOA significant findings that once the load was imposed the response was to approximate the feet and reduce 'toeout'.

CONCLUSION

This reaction of people to reduce their BoS in response to added backpack load appears counter intuitive and raises the question of whether this is maladaptive. Clarification by further investigation will inform backpack wearers to counter this instinctive response to load and increase postural stability.

Balance, Landing Biomechanics, and Functional Movement Screen Characteristics With and Without Knee Exoskeleton in Military Soldiers

INTRODUCTION

A light-weight pneumatic-powered knee exoskeleton could augment mobility and lifting capabilities for a variety of occupational settings. However, added weight/bulkiness and artificially produced knee extension torque could compromise sensorimotor characteristics.

MATERIALS AND METHODS

Ten healthy participants conducted 3 visits within 10 days to the biomechanics laboratory. Participants were asked to complete the following tasks on each visit: single-leg balance, single-leg drop-landing, and select functional movement tasks. Balance characteristics (the ground reaction forces variability and center-of-pressure velocity) were derived from force plates while knee flexion angles during drop-landing and functional movement tasks were captured using a motion capture system. Descriptive statistics as well as paired t-tests or Wilcoxon signed-rank tests were used to compare between conditions. Significance was set at P < .05 a priori.

RESULTS

During single-leg balance, the ground reaction force variabilities were significantly increased (P = .013-.019) and the center of pressure velocity was decreased (P = .001-.017) when wearing knee exoskeleton. During single-leg drop-landing, the exoskeleton condition showed lower knee flexion angles at the initial contact (P = .004-.021) and peak (P = .006-.010). Additionally, the peak vertical ground reaction force was higher in the exoskeleton condition (P = .007). During functional movement tasks, the exoskeleton condition showed less knee flexion range-of-motion during the overhead squat (P = .007-.033) and hurdle step-over (P = .004-.005).

CONCLUSIONS

Participants exhibited stiffer landing technique with the exoskeleton. Given that these compromised sensorimotor characteristics have been associated with musculoskeletal injury risk, modifications to exoskeletons to promote softer landing and greater knee flexion range-of-motion during dynamic activities may be warranted.

Influences of backpack loading on recovery from anterior and posterior losses of balance: An exploratory investigation

Backpacks are common devices for carrying external posterior loads. However, relatively little is known about how these external loads affect the ability to recover from balance loss. In this exploratory investigation, 16 young adults (8 female, 8 male) performed forward and backward lean-and-release balance recovery trials, while wearing a backpack that was unloaded or loaded (at 15% of individual body weight). We quantified the effects of backpack loading on balance recovery in terms of maximum recoverable lean angles, center-of-mass kinematics, and temporal-spatial stepping characteristics. Mean values of maximum lean angles were 20° and 9° in response to forward and backward perturbations, respectively. These angles significantly decreased when wearing the additional load for only backward losses of balance. During backward losses of balance, the additional load decreased peak center-of-mass velocity and increased acceleration by ∼10 and 18% respectively, which was accompanied by ∼5% faster stepping responses and steps that were ∼9% longer, 11% higher, and had an ∼10% earlier onset. Thus, wearing a backpack decreases backward balance recovery ability and changes backward recovery stepping characteristics.

Effect of the Law Enforcement Duty Belt on Muscle Activation during Hip Hinging Movements in Young, Healthy Adults

Sixty percent of all law enforcement officers (LEOs) experience low back pain (LBP), with the LEO duty belt (LEO_DB) commonly reported to be a contributing factor. The primary purpose of the study was to investigate the LEODB's effect on muscular activity and compare it to a tactical vest, which is a commonly used alternative to an LEO_DB. In total, 24 participants (13 male, 11 female; mass, 73.0 ± 11.1 kg; height, 169.0 ± 10.0 cm; age, 24.0 ± 5.8 years) completed a progressive series of hip hinge tasks in a single testing session. All participants completed four conditions (no belt, leather belt, nylon belt, and weight VEST) in a randomized order. Surface electromyography (sEMG) sensors were placed bilaterally on the rectus abdominus, multifidus, biceps femoris, and rectus femoris. Across all tasks, no significant effects of load on muscle activity were found for any of the muscles. Participants rated the VEST condition as more comfortable (p < 0.05) and less restrictive (p < 0.05) than either LEODB. The findings suggest an LEO_DB does not alter muscle activity during bodyweight hip hinging or lifting objects from the ground. Future research should examine whether changes in muscle activity occur with durations of LEO_DB wear more similar to an actual work shift duration for LEOs (≥8 h).

Changing the horizontal position of a fixed backpack load: The effect on postural stability in young adults

BACKGROUND

Modifying the horizontal position of the load in a backpack will change the size of the external torque it creates on the wearer but the effect on postural stability is unclear.

OBJECTIVE

To determine if changing the horizontal position of a fixed backpack load affects postural stability in young adults.

METHODS

A backpack was attached to a steel frame with a bar protruding posteriorly. A fixed load (5% body mass) was placed at three distances along the bar - 0 m, 0.20 m, and 0.40 m. Centre of pressure (CoP) derived measurements were recorded from a force platform sampling at 100 Hz. For each condition participants performed three 90s narrow stance trials with their eyes closed whilst standing on a firm surface. A comparison was made across unloaded (no backpack) and loaded conditions.

RESULTS

There was an immediate decrease in postural stability when a loaded backpack was worn. Only two of the CoP derived measures (Total Excursion - TEx, and Mean Velocity Total Excursion - MVel TEx) differed between the loaded at 0.20 m and loaded at 0 m conditions. All CoP derived measures differed between the loaded at 0.40 m and loaded at 0 m conditions. Furthermore, three of the CoP derived measures (Anterior/Posterior Root Mean Square - A/P RMSq, TEx, and MVel TEx) differed between the loaded at 0.40 m and loaded at 0.20 m conditions.

CONCLUSION

The distribution of a load within a backpack must be carefully considered. The findings for the 0.40 m condition are important for the use and design of large backpacks used by multi-day hikers, travellers, and the military.

Effects of Load Carriage on Postural Sway and Relative Ground Reaction Forces in Special Police Officers: A Cross-Sectional Study

Although excessive load carriage results in biomechanical gait changes, little evidence has been provided regarding its impact on postural sway. Therefore, the main purpose of this study was to determine whether heavier loads have effects on changing foot stability and postural sway in special police officers. Thirty male special police officers (age = 40 ± 6 years, height = 180 ± 5 cm, weight = 89 ± 8 kg) were assessed in four conditions: (1) carrying no load, (2) carrying a 5 kg load, (3) carrying a 25 kg load, and (4) carrying a 45 kg load. Foot characteristics during standing were assessed with Zebris pedobarographic pressure platform. Heavier loads increased the center of pressure (COP) path length and average velocity, length of minor and major axis, and 95% confidence ellipse area, while a decrease in angle between Y and major axis was observed. Relative forces beneath the left forefoot and right backfoot regions decreased and an increase in relative forces beneath the left backfoot and right forefoot was observed. When carrying heavy loads, static foot parameters rapidly changed, especially in COP path length and average velocity.