Unloaded Walking Research Articles

Concentric and eccentric hip musculotendon work depends on backpack loads and walking slopes

Hip muscle weakness is associated with low back and leg injuries. In addition, hiking with heavy loads is linked to high incidence of overuse injuries. Walking with heavy loads on slopes alters hip biomechanics compared to unloaded walking, but individual muscle mechanical work in these challenging conditions is unknown. Using movement simulations, we quantified hip muscle concentric and eccentric work during walking on 0° and ±10° slopes with, and without 40% bodyweight added loads, and with and without a hip belt. For gluteus maximus, psoas, iliacus, gluteus medius, and biceps femoris long head, both concentric and eccentric work were greatest during uphill walking. For rectus femoris and semimembranosus, concentric work was greatest during uphill and eccentric work was greatest during downhill walking. Loaded walking had greater concentric and eccentric work from rectus femoris, biceps femoris long head, and gluteus maximus. Psoas concentric work was greatest while carrying loads regardless of hip belt usage, but eccentric work was only greater than unloaded walking when using a hip belt. Loaded and uphill walking had high concentric work from gluteus maximus, and high eccentric work from gluteus medius and biceps femoris long head. Carrying heavy loads uphill may lead to excessive hip muscle fatigue and heightened injury risk. Effects of the greater eccentric work from hip flexors when wearing a hip belt on lumbar spine forces and pelvic stability should be investigated. Military and other occupational groups who carry heavy backpacks with hip belts should maintain eccentric strength of hip flexors and hamstrings.

Relationships between tibial accelerations and ground reaction forces during walking with load carriage

Peak tibial accelerations (TAs) during running are strongly related to early stance vertical ground reaction forces (GRFs), which are associated with musculoskeletal injury. However, few studies have examined these correlations during walking, and none have evaluated them during walking with loads, a relevant activity for military personnel. Our purpose was to determine the relationships between GRFs and TAs in US Army trainees (n = 649) walking with loads. An inertial measurement unit was attached over their distal antero-medial tibia. Participants walked on an instrumented treadmill at 1.21–1.34 m/s, with a pack loaded with 18.1 kg, for a 3-min warm-up followed by a minimum of 14 strides of data collection. Simple linear regression models were calculated for peak vertical and resultant TAs with vertical and posterior GRF loading rates and peak forces. The strongest relationships were between vertical loading rates and peak vertical TA (R = 0.43–0.50), however the relationships were weaker than has been reported for unloaded walking and running (R > 0.7). All other relationships were trivial to small (R = 0.06–0.27). The weaker relationships for vertical GRFs and TAs may be due to methodological differences between studies, or differences in gait mechanics, such as a longer double-limb support phase in loaded vs. unloaded walking.

Backpack Effects on Two-Dimensional Gait Spatiotemporal and Kinematic Parameters

Loads could affect the body gait in various ways. Backpacks, sling bags, suitcases, and even trolleys could hugely affect human gait without us realizing it. The effects of these loads have been scientifically researched in biomechanics and sports science for the past few years. For instance, the comparison of walking with and without a backpack could easily reveal significant differences in body segments, which could be utilized for therapy and medicine development. The aim of this research is to determine the differences of the spatiotemporal kinematic parameters between a conventional human gait and a backpack-loaded gait. Some parameters to be highlighted are stride lengths, stride duration, joint angles, linear and angular segment positions, velocities, and accelerations. The method used for marker data acquisition is based on the 2-dimensional Direct Linear Transformation. The results demonstrate that the backpack increases stride lengths and reduces stride duration, contrast to the expected where backpacks would reduce stride lengths. It was observed that the angle between the bag and the body posterior affects the abdomen relative angle, which directly translates to stride lengths as well. During unloaded walking, increases in pelvic rotation contribute to increases in stride length with increasing walking speed. However, in loaded walking, the back angle is also a factor in determining kinematic parameters.

Women carry for less: body size, pelvis width, loading position and energetics.

The energetic cost of walking varies with mass and speed; however, the metabolic cost of carrying loads has not consistently increased proportionally to the mass carried. The cost of carrying mass, and the speed at which human walkers carry this mass, has been shown to vary with load position and load description (e.g. child vs. groceries). Additionally, the preponderance of women carriers around the world, and the tendency for certain kinds of population-level sexual dimorphism has led to the hypothesis that women might be more effective carriers than men. Here, I investigate the energetic cost and speed changes of women (N = 9) and men (N = 6) walking through the woods carrying their own babies (mean baby mass = 10.6 kg) in three different positions - on their front, side and back using the same Ergo fabric baby sling. People carrying their babies on their backs are able to maintain their unloaded walking speed (1.4 m/s) and show the lowest increase in metabolic cost per distance (J/m, 17.4%). Women carry the babies for a lower energetic cost than men at all conditions (p < 0.01). Further energetic and kinematic evidence elucidates the preponderance of back-carrying cross-culturally, and illustrates the importance of relatively wider bi-trochanteric breadths for reducing the energetic costs of carrying.

Spatiotemporal and muscle activation adaptations during overground walking in response to lower body added mass

BackgroundLower-extremity exoskeletons have been used in rehabilitation and performance augmentation for the past two decades. An exoskeleton adds a significant load to certain segments of the user’s body and the underlying science about the effects of adding mass to the different lower-body segments is limited. Research questionWhat are the adaptive changes that occur when mass is placed on three lower body segments (pelvis, thigh, and shank)? MethodsHealthy adults (n = 24) completed 5 overground walking trials for 7 added mass conditions. The seven added mass conditions included a Baseline (no-load) condition, + 2 and + 4 lb on either the shanks or the thighs, and + 8 and + 16 lb on the pelvis. Spatiotemporal metrics, surface electromyography (EMG) data from 5 lower-limb muscles, and ground reaction force data were analyzed and compared between conditions. ResultsPelvis mass of 16 lb increased the double support time (p < 0.001) and decreased the single support time (p < 0.001) from the Baseline. Loading rate for none of the added mass conditions were significantly different from the Baseline. The highest activation of the considered thigh muscles and gastrocnemius generally occurred when High Mass was added either to the pelvis or the thigh. SignificanceThe results demonstrate how added mass affects muscle activity, which could inform design of EMG-based exoskeleton controllers. With respect to spatiotemporal changes, results indicate that adding masses equal to or greater than 16 lb on the pelvis can cause significant differences when compared to unloaded walking. This finding implies that all other mass loadings in this study, regardless of location, are regulated. Thus, as a guideline to exoskeleton design, we recommend mass distributions over the pelvis and the thigh to take advantage of the larger muscle groups in adapting to the added mass.

The energetic, kinematic and kinetic responses to load carried on the back, on the head and in a doublepack

The determinants of energy saving phenomena reported for load carried on the head, back and in a doublepack remain unclear. This study compared the energetic, kinematic and kinetic responses to head (H), back (B) and doublepack (DP) loading. Fifteen volunteers walked on an instrumented treadmill at 3 km.h−1 with 0, 3, 12 and 20 kg in each loading method. Whole body motion, ground reaction forces (GRF) and metabolic cost were measured. H was less economical than B (p = 0.014) and DP (p = 0.010). H was also associated with increased step length (p = 0.045), decreased cadence (p = 0.001), greater trunk (p < 0.001) and hip (p < 0.001) extension and greater minimum vertical GRF (p = 0.001) than B and DP. In conclusion, no energy saving was found for head- or back-loading but economy may be improved with methods that cause smaller perturbations from unloaded walking. Practitioner summary: Energy saving phenomena have been reported for load carried on the head, back and in a doublepack, yet the determinants are unclear. This study shows that smaller perturbations from unloaded to loaded walking are associated with improved economy for certain load carriage conditions, such as the doublepack.

A backpack load sharing model to evaluate lumbar and hip joint contact forces during shoulder borne and hip belt assisted load carriage

Musculoskeletal injuries of the lumbar spine occur frequently among military service members and are associated with heavy backpack loads. Musculoskeletal modeling and simulation facilitate biomechanical evaluation to compare different backpack designs. We developed a backpack attachment model that can be tuned to represent various load distributions between the torso and pelvis. We generated walking simulations to estimate muscle and joint contact forces of unloaded walking and while carrying 38 kg using shoulder-borne backpacks and hip belt-assisted backpacks for six U.S. Marines. Three-dimensional peak and average lumbar (L4-L5) and hip joint contact forces over the stance phase were compared between each load condition. Axial L4-L5 and axial and anterior hip joint contact forces were greater during both backpack conditions compared to the unloaded condition. Joint contact forces were similar between backpack conditions. Future studies incorporating additional participants, walking conditions, and backpack load distributions are suggested for further model development and backpack design evaluation.

Physiological Factors of Importance for Load Carriage in Experienced and Inexperienced Men and Women.

The ability to carry heavy loads is an important and necessary task during numerous outdoor activities and especially in military operations. The aim of this study was to investigate factors associated with load-carrying ability in men and women with and without extensive load-carrying experience. The energy expenditure during carrying no load, 20, 35, and 50kg at 2 walking speeds, 3 and 5kmh-1, was studied in 36 healthy participants, 19 men (30±6years, 82.5±7.0kg) and 17 women (29±6years, 66.1±8.9kg), experienced (>5years) in carrying heavy loads (n=16, 8 women) or with minor or no such experience (n=20, 9 women). A standard backpack filled with weights to according carry load was used during the walks. Anthropometric data, leg muscle strength, as well as trunk muscle endurance and muscle fiber distribution of the thigh, were also obtained. Extra Load Index (ELI)-the oxygen uptake (VO2) during total load over unloaded walking-was used as a proxy for load-carrying ability at 20, 35, and 50kg (ELI20, ELI35, and ELI50, respectively). In addition to analyzing factors of importance for the ELI values, we also conducted mediator analyses using sex and long-term carrying experience as causal variables for ELI as the outcome value. The study was approved by the Regional Ethics Committee in Stockholm, Sweden. For the lowest load (20kg), ELI20, was correlated with body mass but no other factors. Walking with 35 and 50kg load at 5kmh-1 body mass, body height, leg muscle strength, and absolute VO2max were correlated, while relative VO2max, trunk muscle endurance, and leg muscle fiber distribution were not correlated to ELI35 and ELI50.ELI50 at 5kmh-1 differed between the sexes. This difference was only mediated by the difference in body mass. Neither muscle fiber distribution, leg muscle strength, trunk muscle endurance, and body height nor did absolute or relative VO2max explain the difference.Participants with long-term experience of heavy load carrying had significant lower ELI20 and ELI50 values than those with minor or no experience, but none of the above studied factors could explain this difference. The study showed that body mass, without sex differences, and experience of carrying heavy loads are the dominant factors for the ability to carry heavy loads. Even though the effect of experience alludes to the need for extensive carrying training, no causality can be proven. Load carry training intervention studies is suggested for future investigations.

Spatial-temporal and kinematic characteristics of gait carrying loaded backpack with elastic straps

Objective: Applying 3D Motion Capture technology to analyze the kinematic and spatial temporal characteristics of gait when carrying loaded backpacks with elastic straps, the study investigates the effect of backpacks with elastic-strap on fatigue during walking. Methods: Ten healthy male undergraduates did not do strenuous or fatigue exercise two days before the trials and served as subjects (aged 19 ? 1.8 years). All subjects provided a written and oral explanation of the trial procedures. In two trials departed by two days apart, the subjects randomly carried one of the two kinds of backpacks ( with non-elastic straps or with elastic straps backpacks loaded the same weight books (about 10% of their bodyweight). After pasted with markers as the guide of the Vicon 3D motion capture system, the subjects walked on the treadmill at 4.5 km/h for 20 min in each trial. Before and after each walking trial, the gait parameters of the subjects were measured by a 6 meters-long plantar pressure test plate(Zebras FDM System). Results: The change of the COP and the change of the gait parameters in the subjects with elastic straps backpacks after 20 min walking were relatively less than those with no elastic-strap backpacks, showing better stability and delaying fatigue. From this statement, it can be reasoned that being able to reduce the effect of the load on the person by returning the gait pattern closer to an unloaded walking pattern may reduce problems associated with loaded carriage. The elastic straps decreased the elevation of the mean vertical position of the backpack and create a gap between the shoulders and the shoulder pads. Conclusion: The decompression backpack with elastic straps shows the effect of protecting the user?s spine and in delaying the cervical back muscle fatigue, during walking at appropriate pace maybe reduce the risk of musculoskeletal injuries and muscle fatigue associated with carrying heavy backpack loads while reducing the metabolic cost of loaded walking.

Gender and Parity in Statistical Prediction of Anterior Carry Hand-Loads from Inertial Sensor Data.

The objective of this study was to examine potential gender effects on the performance of a statistical algorithm for predicting hand-load levels that uses body-worn inertial sensor data. Torso and pelvic kinematic data was obtained from 11 men and 11 women in a laboratory experiment while they carried anterior hand-loads of 13.6 kg, and 22.7 kg, and during unloaded walking. Nine kinematic variables expressed as relative changes from unloaded gait were calculated and used as predictors in a statistical classification model predicting load-level (no-load, 13.6 kg, and 22.7 kg). To compare effects of gender on prediction accuracy, prediction models were built using both, gender-balanced gait data and gender-specific data (i.e., separate models for men and women) and evaluated using hold-out validation techniques. The gender-balanced model correctly classified load levels with an accuracy of 74.2% and 80.0% for men and women, respectively. The gender-specific models had accuracies of 68.3% and 85.0% for men and women, respectively. Findings indicated a lack of classification parity across gender, and possibly across other types of personal attributes such as age, ethnicity, and health condition. While preliminary, this study hopes to draw attention to challenges in algorithmic bias, parity and fairness, particularly as machine learning techniques gain popularity in ergonomics practice.

Adaptation in Gait to Body-Weight Unloading

Modifications in load-related sensory input during unloaded walking can lead to recalibration of the body schema and result in aftereffects. The main objective of this study was to identify the adaptive changes in gait and body-weight perception produced by unloaded walking. Gait performance during treadmill walking was assessed in 12 young participants before and after 30 min of unloaded walking (38% body weight) by measuring lower limb kinematics, temporal gait measures, and electromyography (EMG). A customized weight-perception scale was used to assess perception of body weight. Participants perceived their body weight to be significantly heavier than normal after unloading while walking. Angular displacement about ankle and knee was significantly reduced immediately after unloaded walking, while temporal gait parameters remained unchanged. The EMG activity in some muscles was significantly reduced after unloading. These findings indicate that walking at reduced body weight results in alterations in segmental kinematics, neuromuscular activity, and perception of body weight, which are the aftereffects of motor adaptation to altered load-related afferent information produced by unloading. Understanding the adaptive responses of gait to unloading and the time course of the aftereffects will be useful for practitioners who use body-weight unloading for rehabilitation.

Effects of infant transportation on lower extremity joint moments: Baby carrier versus carrying in-arms

BackgroundThe act of babywearing is recognizably a task of load carriage and has gained popularity among millennial caregivers. Research QuestionThe implications of babywearing on lower extremity joint moments of the caregiver are still unknown during prolonged transport and a direct comparison of babywearing to carrying an infant in-arms has not been previously conducted. MethodsEighteen females participated in this study by performing 3 conditions: a) 3 min walking unloaded (UL), b) 15 min walking while carrying a mannequin infant in-arms (IA), and c) 15 min walking while wearing a mannequin infant in an anteriorly positioned baby carrier (BC). Two separate data analyses were conducted using a repeated measures ANOVA. First, UL compared to the initial minute of walking for IA and BC. Second, UL compared to the final minute of walking for IA and BC. ResultsDuring initial minute comparisons, both IA and BC conditions increased joint moments in the frontal and sagittal plane at the knee with no change at the ankle and hip. During final minute comparisons, IA maintained the increases in the knee frontal plane joint moments observed during initial minute comparisons but also increased at the hip; however, BC generally showed no statistical difference from UL. Carrying an infant in a baby carrier more closely resembles unloaded walking, while carrying an infant in-arms appears to increase the mechanical load placed on the knee and hip joints in the frontal plane through an increase in joint moments. SignificanceDuring prolonged transportation, caregivers might choose to employ a baby carrier as opposed to carrying an infant in-arms, as in-arm carriage increases the loading knee abduction moment by 8.7% and the loading knee extension moment by 16.7%.

Tibiofemoral joint contact forces increase with load magnitude and walking speed but remain almost unchanged with different types of carried load.

Musculoskeletal injuries (MSI) in the military reduce soldier capability and impose substantial costs. Characterizing biomechanical surrogates of MSI during commonly performed military tasks (e.g., load carriage) is necessary for evaluating the effectiveness of possible interventions to reduce MSI risk. This study determined the effects of body-borne load distribution, load magnitude, and walking speed on tibiofemoral contact forces. Twenty-one Australian Army Reserve soldiers completed a treadmill walking protocol in an unloaded condition and wearing four armor types (standard-issue and three prototypes) with two load configurations (15 and 30 kg) for a total of 8 armor x load ensembles. In each ensemble, participants completed a 5-minute warm-up, and then walked for 10 minutes at both moderate (1.53 m⋅s-1) and fast (1.81 m⋅s-1) speeds. During treadmill walking, three-dimensional kinematics, ground reaction forces, and muscle activity from nine lower-limb muscles were collected in the final minute of each speed. These data were used as inputs into a neuromusculoskeletal model, which estimated medial, lateral and total tibiofemoral contact forces. Repeated measures analyses of variance revealed no differences for any variables between armor types, but peak medial compartment contact forces increased when progressing from moderate to fast walking and with increased load (p<0.001). Acute exposure to load carriage increased estimated tibiofemoral contact forces 10.1 and 19.9% with 15 and 30kg of carried load, respectively, compared to unloaded walking. These results suggest that soldiers carrying loads in excess of 15 kg for prolonged periods could be at greater risk of knee MSI than those with less exposure.

Predicting Ground Reaction Force from a Hip-Borne Accelerometer during Load Carriage.

Ground reaction forces (GRF) during load carriage differ from unloaded walking. Methods to quantify peak vertical GRF (pGRFvert) of Soldiers walking with loads outside of a laboratory are needed to study GRF during operationally relevant tasks. Develop a statistically based model to predict pGRFvert during loaded walking from ActiGraph GT3X+ activity monitor (AM) vertical acceleration. Fifteen male Soldiers (25.4 ± 5.3 yr, 85.8 ± 9.2 kg, 1.79 ± 9.3 m) wore an ActiGraph GT3X+ AM over their right hip. Six walking trials (0.67-1.58 m·s) with four loads (no load, 15, 27, 46 kg) and two types of footwear (athletic shoes and combat boots) were completed on an instrumented force plate treadmill. Average peak vertical AM acceleration (pACCvert) and pGRFvert were used to develop a regression equation to predict pGRFvert. The model was validated using a leave-one-subject-out approach. Root mean square error (RMSE) and average absolute percent difference (AAPD) between actual and predicted pGRFvert were determined. pGRFvert was also predicted for two novel data sets and AAPD and RMSE calculated. The final equation to predict pGRFvert included pACCvert, body mass, carried load mass, and pACCvert-carried load mass interaction. Cross-validation resulted in an AAPD of 4.0% ± 2.7% and an RMSE of 69.5 N for leave-one-subject-out and an AAPD of 5.5% ± 3.9% and an RMSE of 78.7 N for the two novel data sets. A statistically based equation developed to predict pGRFvert from ActiGraph GT3X+ AM acceleration proved to be accurate to within 4% for Soldiers carrying loads while walking. This equation provides a means to predict GRF without a force plate.

Weighted Walking Influences Lower Extremity Coordination in Children on the Autism Spectrum.

There is sparse quantitative research regarding gait coordination patterns of children on the autism spectrum, though previous studies, relying only upon observational data, have alluded to characteristically poor movement coordination. This study compared walking with a weighted vest, a backpack carriage, and an unloaded walking condition on lower extremity coordination among 10 male children (aged 8-17 years) on the autism spectrum. All participants completed 15 gait trials in the following three conditions: (a) unloaded, (b) wearing a backpack weighted with 15% body mass, and (c) wearing a vest weighted with 15% body mass. We used continuous relative phase analysis to quantify lower extremity coordination and analyzed data through both group and single-subject comparisons. We used the Model Statistic to test for statistical significance at each of the normalized data points for each segment couple (thigh-leg, leg-foot, and thigh-foot). The first 10 and last 10 stride blocks were tested for possible accommodation strategies. Group comparisons revealed no coordination changes among the three conditions (likely due to insufficient statistical power), while single-subject comparisons exposed significant decreased variability in gait coordination patterns ( p < .05) in both loaded conditions, relative to the unloaded condition. These participants exhibited variable coordination patterns during the unloaded gait. When walking with loads, coordination pattern variability of the lower extremities was decreased. This finding suggests that walking while carrying or wearing heavy objects may reduce the number of potential motor pattern choices and thus decrease the overall variability of lower extremity movement patterns. Additional research with a larger and more diverse participant sample is required to confirm this conclusion.

Sling-based infant carrying affects lumbar and thoracic spine neuromechanics during standing and walking

BackgroundRegular infant carrying might be a contributing factor for the development and progression of low back and pelvic girdle pain in mothers after childbirth. However, the neuromechanical adaptations of the spine due to different sling-based carrying techniques are not sufficiently well understood in order to provide evidence-based carrying recommendations. Research questionWhat are the immediate effects of different sling-based infant carrying techniques on trunk neuromechanics? MethodsUsing a Vicon motion capture and a wireless surface electromyography system, three-dimensional pelvis and spinal kinematics as well as activation patterns of eight trunk muscles were derived from fifteen healthy young women during upright standing and level walking without carrying a load and while carrying a 6 kg-dummy with a sling in front and on either side. Data were analyzed using Statistical Parametric Mapping, allowing group comparisons of discrete parameters (standing) as well as continuous data (walking). To distinguish between clinically relevant and clinically not relevant kinematic findings, statistically significant differences were only considered in case of ≥5°. ResultsCompared to unloaded walking, carrying the dummy in front was mainly associated with increased lumbar lordosis (standing: (Δ8.8°, p = 0.006; walking: (Δ ≥ 8.2°, 1–100% of gait cycle [%GC], p < 0.001). When carrying the dummy on the preferred side, increased thoracic kyphosis (standing: ≥6.4°, p ≤ 0.003; walking: Δ ≥ 5.6°, 1–100%GC, p < 0.001) and axial rotation towards the ipsilateral side (standing: Δ5.3°, p = 0.003; walking: Δ ≥ 5.0°, 46–58%GC, p = 0.002) were observed. All three conditions entailed increased paraspinal muscle activity during walking, although only unilaterally in side carrying (lumbar, preferred condition: Δ ≥ 13.2%maxMVIC, 49–57%GC, p < 0.001; thoracic, non-preferred condition: Δ ≥ 5.3%maxMVIC, 47–58%GC, p < 0.001). SignificanceCarrying an infant alternating on both sides using a sling could be advantageous for preventing musculoskeletal pain resulting from excessive lumbar hyperextension and paraspinal muscle hyperactivation in women after childbirth.

Biomechanical Model for Stress Fracture-related Factors in Athletes and Soldiers.

This study aimed to develop a computational biomechanical model of strain in human tibial bone that will facilitate better understanding of the pathophysiology of SF. The MRI of a healthy, young male was used for full anatomical segmentation of the calf tissues, which considered hard-soft tissues biomechanical interactions. From the undeformed coronal MR images, the geometry of bones, muscles, connecting ligaments, and fat were reconstructed in three dimensions and meshed to a finite element model. A force that simulated walking was applied on the tibial plateaus. The model was then analyzed for strains in the tibia under various conditions: unloaded walking, walking with a load equivalent to 30% of bodyweight, and walking under conditions of muscular fatigue. In addition, the effect of tibia robustness on strain was analyzed. The model showed that the tibia is mostly loaded by compression, with maximal strains detected in the distal anterior surface: 1241 and 384 microstrain, compressive and tensile, respectively. Load carriage resulted in ~30% increase in maximal effective strains. Muscle fatigue has a complex effect; fatigued calf muscles (soleus) reduced the maximal effective strains up to 9%, but fatigued thigh muscles increased those strains by up to 3%. It had also been shown that a slender tibia is substantially prone to higher maximal effective strains compared with an average (22% higher) or robust tibia (39% higher). Thigh muscle fatigue, load carriage, and a slender tibia were detected as factors that may contribute to the development of SF. The methodology presented here is a novel tool for investigating the pathophysiology of SF.

Effect of carrying different military equipment during a fatigue test on shooting performance

This study investigated the effect of a 3-km walking test (3kWT) carrying different military equipment on shooting performance, rating of perceived exertion (RPE), heart rate (HR), and test time. The relative combat wear and backpack weight (as percentage of soldier’s body weight [%BW]) was reported and, along with HR, its relationship to marksmanship variables was tested. Thirty-nine Spanish Army males walked as fast as possible to complete the 3kWT in the following conditions in a randomized order: unloaded walking; wearing the combat uniform; and carrying the combat uniform plus combat backpack. A shooting test was completed before and after the 3kWT. The HR and RPE were evaluated. The marksmanship variables and HR were analysed using a two-way repeated measures ANOVA, and a repeated ANOVA was also used for 3kWT completion time and HR reserve analysis. Correlation analyses were performed between the equipment’s weight, HR, and marksmanship variables. The results showed that shooting score decreased after the 3kWT in both load conditions (p < 0.001). The 3kWT time, RPE, and HR increased from control to load conditions, and also between load conditions. The HR reserve showed no significant effects between conditions. The %BW of the backpack condition negatively influenced aiming accuracy (r = −0.35; p = 0.04) and cleanness triggering (r = 0.37; p = 0.03). Correlations between HR and shooting variables were non-significant. In conclusion, wearing the Spanish Army combat wear and backpack resulted in shooting performance degradation. Furthermore, fatigue and RPE increased and this could decrease physical marksmanship and performance capacity in combat situations.

The effects of different carrying methods on locomotion stability, gait spatio-temporal parameters and spinal stresses

Manual material handling (MMH) contributes to a large percentage of musculoskeletal disorders. One of its fundamental activities is load carrying that can be accomplished in several strategies, with each one imposing different types of stresses on the musculoskeletal system. Therefore, the first goal of this study was to determine the effect of different carrying methods on walking stability using motion capture analysis. Second, to analyze gait adaptations to stresses associated with load carrying in order to prevent falling. Third, to investigate the effect of these stresses coupled with human body adjustment on the forces at the L5/S1 disc. Thirty participants carried 10 and 30 lbs loads via frontal, lateral, bilateral, and posterior carriages. Frontal and lateral methods generated the most unstable conditions compared to the others. The unstable locomotion forced the gait parameters to be significantly altered in order to maintain stability. Additionally, the postures maintained in these conditions resulted in significantly high compression and shear forces acting at the L5/S1 disc when compared to the other carrying methods. Moreover, heavier weights exacerbated the effect on the dependent variables. Notably, bilateral and posterior carrying methods provided results comparable to the unloaded walking baseline. In conclusion, to reduce the potential risks associated with load carrying, the recommendation to split the load between both hands using bilateral carrying method or carrying it posteriorly should be taken into account while designing MMH activities.

Effect of stable and unstable load carriage on walking gait variability, dynamic stability and muscle activity of older adults

Load carriage perturbs the neuromuscular system, which can be impaired due to ageing. The ability to counteract perturbations is an indicator of neuromuscular function but if the response is insufficient the risk of falls will increase. However, it is unknown how load carriage affects older adults. Fourteen older adults (65 ± 6 years) attended a single visit during which they performed 4 min of walking in 3 conditions, unloaded, stable backpack load and unstable backpack load. During each walking trial, 3-dimensional kinematics of the lower limb and trunk movements and electromyographic activity of 6 lower limb muscles were recorded. The local dynamic stability (local divergence exponents), joint angle variability and spatio-temporal variability were determined along with muscle activation magnitudes. Medio-lateral dynamic stability was lower (p = 0.018) and step width (p = 0.019) and step width variability (p = 0.015) were greater in unstable load walking and step width variability was greater in stable load walking (p = 0.009) compared to unloaded walking. However, there was no effect on joint angle variability. Unstable load carriage increased activity of the Rectus Femoris (p = 0.001) and Soleus (p = 0.043) and stable load carriage increased Rectus Femoris activity (p = 0.006). These results suggest that loaded walking alters the gait of older adults and that unstable load carriage reduces dynamic stability compared to unloaded walking. This can potentially increase the risk of falls, but also offers the potential to use unstable loads as part of fall prevention programmes.