The effect of the weight of equipment on muscle activity of the lower extremity in soldiers

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).

Effects of Law Enforcement Load Carriage Systems on Muscle Activity and Coordination during Walking: An Exploratory Study

Law enforcement officers (LEOs) commonly wear a duty belt (DB) or tactical vest (TV) and from prior findings, these forms of load carriage (LC) likely alter muscular activity. However, studies on the effects of LEO LC on muscular activity and coordination are limited in the current literature. The present study examined the effects of LEO load carriage on muscular activity and coordination. Twenty-four volunteers participated in the study (male = 13, age = 24.5 ± 6.0 years). Surface electromyography (sEMG) sensors were placed on the vastus lateralis, biceps femoris, multifidus, and lower rectus abdominus. Participants completed treadmill walking for two load carriage conditions (duty belt and tactical vest) and a control condition. Mean activity, sample entropy and Pearson correlation coefficients were computed for each muscle pair during the trials. The duty belt and tactical vest resulted in an increase in muscle activity in several muscles; however, no differences between the duty belt and tactical vest were found. Consistently across the conditions, the largest correlations were observed between the left and right multifidus (r = 0.33-0.68) and rectus abdominus muscles (0.34-0.55). There were statistically small effects (p < 0.05, η² = 0.031 to 0.076) of the LC on intermuscular coordination. No effect (p > 0.05) of the LC on sample entropy was found for any muscle. The findings indicate that LEO LC causes small differences in muscular activity and coordination during walking. Future research should incorporate heavier loads and longer durations.

Impact of Backpacks on Ergonomics: Biomechanical and Physiological Effects: A Narrative Review

(1) Background: the effects of load carriage packs on human gait biomechanics, physiology and metabolism depend on the weight carried, the design of the pack and its interaction with the user. (2) Methods: An extensive search in the PubMed database was performed to find all the relevant articles using the following keywords: backpack, rucksack, backpack ergonomy and sports backpack; 60 articles were included. (3) Results and significance: Double pack (DP) and T-pack (TP) designs are recommended solutions for school children, compared with backpacks (BP). For soldiers and hikers, a backpack remains the best compromise. A hip belt is recommended for BPs as well as for the back of DPs. Shorter and stiffer shoulder straps combined with a higher and tighter load placement on the back provide the best combination in terms of balance, muscle activation and energy expenditure. It is, therefore, possible to determine guidelines for designing the optimal load carriage system, depending on the application. (4) Conclusions: based on the available evidence, DP and TP are advantageous in terms of posture. DP is better than conventional BPs in terms of balance and muscle activation, but has the disadvantage of limited visibility, thermal sensation and obstructed ventilation. In general, it is desirable not to exceed 40% of body mass (BM).

Gait and neuromuscular dynamics during level and uphill walking carrying military loads

The neuromuscular system responds to perturbation and increasing locomotor task difficulty by altering the stability of neuromuscular output signals. The purpose of this study was to determine the effects of two different military load carriage systems on the dynamic stability of gait and muscle activation signals. 14 army office cadets (20 ± 1 years) performed 4-minute treadmill walking trials on level (0%) and uphill (10%) gradients while unloaded, and with 11 kg backpack and 11 kg webbing loads while the activity of 6 leg and trunk muscles and the motion of the centre of mass (COM) were recorded. Loaded and uphill walking decreased stability and increased magnitude of muscle activations compared to loaded and level gradient walking. Backpack loads increased the medio-lateral stability of COM and uphill walking decreased stability of vertical COM motion and increased stride time variability. However, there was no difference between the two load carriage systems for any variable. The reduced stability of muscle activations in loaded and uphill conditions indicates an impaired ability of the neuromuscular control systems to accommodate perturbations in these conditions which may have implications on the operational performance of military personnel. However, improved medio-lateral stability in backpack conditions may indicate that participants were able to compensate for the loads used in this study, despite the decreased vertical stability and increased stride time variability evident in uphill walking. This study did not find differences between load carriage systems however, specific load carriage system effects may be elicited by greater load carriage masses.Highlights Loaded and uphill walking decreased dynamic stability of muscle activationsLower activation stability indicates impaired neuromotor resistance to perturbationBackpack and webbing loads produced similar effects on muscle activations.

Military load carriage effects on the gait of military personnel: A systematic review

Carrying heavy loads results in biomechanical changes to gait and to an increased risk of injury in soldiers. The aim of this review is to examine the effects of military specific load carriage on the gait of soldiers. The Web of Science, PubMed and CINAHL databases were searched, a total of 1239 records were screened and 20 papers were included in the review. Participant, load and task characteristics and a summary of key findings were extracted. Due to heterogeneity in the reviewed studies, analysis was restricted to qualitative synthesis. There were limited effects on spatio-temporal variables but consistently reported increased trunk, hip and knee flexion and increased hip and knee extension moments. Muscle activation of lower limb and trunk muscles were also increased with loads. However, there were some conflicting findings for most parameters reviewed and apart from spatio-temporal parameters the findings of this review were in line with previous reviews of combined military and civilian populations.

Dynamic Postural Stability in Active, Adolescent Males Following Repeated Bouts of Aerobic Exercise in Hot and Temperate Environments: A Pilot Study

Introduction

Proper jump-landing neuromuscular control is crucial in mitigating lower-extremity musculoskeletal injuries. The presence of fatigue, especially in extreme environments, may degrade dynamic postural stability (DPS) and result in lower-extremity injuries. This study aimed to evaluate the influence of moderate intensity exercise in hot (HOT) and temperate (TEMP) ambient temperatures and residual effects of a previous bout on DPS during a single-legged jump-landing. It was hypothesized that the participants would display worse DPS after HOT compared to TEMP.

Methods

Six recreationally active young males (16.8 ± 0.7 year, 1.88 ± 0.12 m, 83.8 ± 19.8 kg) completed two, 60-minute bouts of exercise with 60 minutes of rest between bouts in both HOT (35°C) and TEMP (22.2°C). Heart rate and core body temperature (T_c) were monitored continuously, and DPS was assessed before and after each bout.

Results

The DPS time and condition effects were not identified (p > 0.05), but HOT elicited some notable (d > 0.20) increases in heart rate, T_c, and DPS compared to TEMP.

Conclusions

The DPS decrements varied between subjects suggesting individual-specific etiology. Repeated bouts of exercise in HOT may place an individual at a greater risk for injury than TEMP if proper prevention strategies are not used.

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

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

Effect of uphill walking with varying grade and speed during load carriage on muscle activity

Indian soldiers, while guarding the mountainous border areas, often carry loads in steep uphill gradients. This activity may predispose the risk of muscle injury. The present study aimed to examine the effects of an increasing load, speed and gradient during incremental uphill treadmill walking on different muscles. Twelve infantry soldiers walked on a treadmill at two speeds (2.5 and 4 km/h) with no load, and carrying 10.7, 17 and 21.4 kg loads at 0, 5, 10, 15, 20, 25% gradients. Electromyographic responses of erector spinae (>240%) and vastus medialis (>240%) were mostly affected, followed by soleus (>125%) and gastrocnemius medialis (>100%) at maximum speed, load and gradient combination compared to 0% gradient. Carrying 10.7 kg at 15% gradient and above was found to be highly strenuous and fatiguing with the risk of muscle injury. Uphill load carriage in slower speed is recommended for the maintenance of combat fitness of the individual at higher gradients. Practitioner Summary: The present article has evaluated the stress encountered by soldiers during load carriage at incremental uphill gradients while walking at different speeds by recording the muscular activities. Load carriage in steep uphill gradients is highly strenuous and may lead to muscle injury thus compromising the combat fitness.

The effect of backpack load on muscle activities of the trunk and lower extremities and plantar foot pressure in flatfoot

[Purpose] The purpose of this study was to investigate the changes in muscle activation of the trunk and lower extremities and plantar foot pressure due to backpack loads of 0, 10, 15, and 20% of body weight during level walking in individuals with flatfoot. [Methods] Fourteen young flatfoot subjects and 12 normal foot subjects participated in this study. In each session, the subjects were assigned to carry a backpack load, and there were four level walking modes: (1) unloaded walking (0%), (2) 10% body weight (BW) load, (3) 15% BW load, and (4) 20% BW load. Trunk and lower extremity muscle activities were recorded by surface EMG, and contact area and plantar foot pressure were determined using a RS scan system. [Results] The erector spinae, vastus medialis, tibialis anterior and gastrocnemius muscle activities, but not the rectus femoris and rectus abdominis muscle activities of flatfoot subjects significantly and progressively increased as load increased in flatfoot subjects. Contact area and pressure of the lateral and medial heel zones were significantly increased too. [Conclusion] Based on this data, the weight of a backpack could influence muscle activation and plantar foot pressure in flatfoot.

Effects of wearing different personal equipment on force distribution at the plantar surface of the foot

Background. The wearing of personal equipment can cause specific changes in muscle activity and posture. In the present study, we investigated the influence of differences in equipment related weight loading and load distribution on plantar pressure. In addition, we studied functional effects of wearing different equipment with a particular focus on relevant changes in foot shape. Methods. Static and dynamic pedobarography were performed on 31 male soldiers carrying increasing weights consisting of different items of equipment. Results. The pressure acting on the plantar surface of the foot increased with higher loading, both under static and dynamic conditions (p < 0.05). We observed an increase in the contact area (p < 0.05) and an influence of load distribution through different ways to carry the rifle. Conclusions. The wearing of heavier weights leads to an increase in plantar pressure and contact area. This may be caused by flattening of the transverse and longitudinal arches. The effects are more evident in subjects with flat feet deformities which seem to flatten at an earlier load condition with a greater amount compared to subjects with normal arches. Improving load distribution should be a main goal in the development of military equipment in order to prevent injuries or functional disorders of the lower extremity.