Load Carriage Research Articles

Soldier Load Carriage, Injuries, Rehabilitation and Physical Conditioning: An International Approach.

Soldiers are often required to carry heavy loads that can exceed 45 kg. The physiological costs and biomechanical responses to these loads, whilst varying with the contexts in which they are carried, have led to soldier injuries. These injuries can range from musculoskeletal injuries (e.g., joint/ligamentous injuries and stress fractures) to neurological injuries (e.g., paresthesias), and impact on both the soldier and the army in which they serve. Following treatment to facilitate initial recovery from injuries, soldiers must be progressively reconditioned for load carriage. Optimal conditioning and reconditioning practices include load carriage sessions with a frequency of one session every 10–14 days in conjunction with a program of both resistance and aerobic training. Speed of march and grade and type of terrain covered are factors that can be adjusted to manipulate load carriage intensity, limiting the need to adjust load weight alone. Factors external to the load carriage program, such as other military duties, can also impart physical loading and must be considered as part of any load carriage conditioning/reconditioning program.

An ergonomic intervention for manual load carrying on Indian farms

The farm inputs like seeds, fertilizers and produce are handled manually in most of the low-income and underdeveloped countries. Such practice of manual load carrying is one of the dominant contributors to back pain and associated physiological problems.In the present study, it was found that volume, quantum and distance determine the mode of load carrying. Bulky or voluminous commodities like harvested cereal crops and fodder are carried on the head. Heavy loads of paddy and vegetables filled in gunny bags, which limits the volume to bag size are carried on the back. Carrying the load on the head is by and large prevailing mode because it does not introduce eccentricity and postures remain balanced., In the present study, an attempt is made to develop a harness, which does not alter the head loading but prevents the loading of the spine. Three approaches considered were: Approach-I (harness H1): load passing through shoulders only (one path only); Approach II (harness H2): load passing through head and shoulder (through two paths only); Approach III (harness H3): Load passing through head and shoulder (through two paths), but in this approach, load on the cervical spine was limited to 10 kg and rest of the load was transferred to shoulder with proper stability. The outcome of ergonomic studies showed that Approach-III is the most metaboliclly economical, compared to other developed approaches and could be adopted for Indian agricultural farm load carriage for various purposes.

Lower Limb Biomechanical Responses During a Standardized Load Carriage Task are Sex Specific.

The purpose of this study was to investigate sex-specific lower limb biomechanical adaptations during a standardized load carriage task in response to a targeted physical training program. Twenty-five healthy civilians (males [n = 13] and females [n = 12]) completed a load carriage task (5 km at 5.5 km·h-1, wearing a 23 kg vest) before and after a 10-week lower-body-focused training program. Kinematics and ground reaction force data were collected during the task and were used to estimate lower limb joint kinematics and kinetics (i.e., moments and powers). Direct statistical comparisons were not conducted due to different data collection protocols between sexes. A two-way repeated measures ANOVA tested for significant interactions between, and main effects of training and distance marched for male and female data, respectively. Primary kinematic and kinetic changes were observed at the knee and ankle joints for males and at the hip and knee joints for females. Knee joint moments increased for both sexes over the 5 km distance marched (P > .05), with males demonstrating significant reductions in peak knee joint extension after training. Hip adduction, internal rotation, and knee internal rotation angles significantly increased after the 5 km load carriage task for females but not males. Differences in adaptive gait strategies between sexes indicate that physical training needs to be tailored to sex-specific requirements to meet standardized load carriage task demands. The findings highlighted previously unfound sex-specific responses that could inform military training and facilitate the integration of female soldiers into physically demanding military roles.

The Influence of Load Carriage on Knee Joint Loading and Metabolic Cost on Walking with Lower-Limb Amputation: A Preliminary Modeling Study

ABSTRACT Introduction For able-bodied individuals, the mechanical output from the ankle muscles is modulated to meet the altered demands of load carriage. However, for individuals with a lower-limb amputation, the stiffness properties of standard-of-care prosthetic feet do not change with varying load conditions. Thus, individuals with amputation often develop gait asymmetries during load carriage that increase their risk for developing overuse injuries such as in the intact knee and increase the metabolic cost of walking relative to able-bodied individuals. The purpose of this preliminary study was to assess the influence of load carriage technique on knee joint loading and metabolic cost during gait of an individual with a below-knee amputation using a forward dynamics simulation framework. Methods Simulations were generated to track the experimental walking data of individuals with amputation for 3 loading conditions (unloaded, front load, and back load). Results These simulations showed that individuals with amputation rely on their intact limb as a compensatory strategy to meet the increased demands of carrying a load. Carrying a back load was found to increase intact knee joint loading relative to carrying a front load but reduced metabolic cost. Conclusion The tradeoff between joint loading and metabolic cost should be considered when determining the appropriate load carriage technique. Future work should focus on improving prosthetic foot designs to help reduce joint loading asymmetry and elevated metabolic cost during different loading conditions for individuals with lower-limb amputation.

Increased nasal Streptococcus pneumoniae presence in Western environment associated with allergic conditions in Chinese immigrants.

Chinese immigrants living in Australia experience increased allergic conditions: asthma, eczema, hay fever and wheeze. Recently we reported diminished innate cytokine responses in long-term immigrants, potentially increasing their pathogenic viral load and microbial carriage. We hypothesise that a Western environment changes the nasal microbiome profile, and this altered profile may be associated with the development of allergic conditions. In this cross-sectional study, we aimed to examine the loading of viral and microbial respiratory pathogens in the upper airway. Adult Chinese immigrants were grouped depending on time spent in Australia: short-term (<6 years) or long-term (≥6 years). First, age- and gender-matched immigrants were selected for an initial screen using quantitative polymerase chain reaction (qPCR) micro-array panels. Then based on initial results the viruses, human parainfluenza 3 and rhinovirus, and the bacteria, Burkholderia spp., Staphylococcus aureus and Streptococcus pneumoniae, were validated using qPCR in the population. Associations for bacterial prevalence with atopic phenotypes were investigated. Pooling the initial screen and validation subjects, S. aureus and S. pneumoniae had higher prevalence in long-term compared with short-term subjects (25.0% vs 8.1%, P=0.012; and 76.8% vs 48.4%, P=0.002). Those immigrants with nasal S. pneumoniae presence resided longer (average time 90.4 months) in Australia than immigrants without S. pneumoniae (52.7 months; P=0.001). After adjusting for confounders, Chinese immigrants with S. pneumoniae carriage have a five-fold increased risk of doctor-diagnosed eczema (odds ratio, OR 5.36, 95% CI: 1.10-26.14; P=0.038) compared to immigrants without S. pneumoniae carriage. There was a trend of S. pneumoniae abundance correlating with reduced host Toll-like receptor gene expression. Our findings suggest that nasal S. pneumoniae may play a role in the development of allergic conditions in Chinese immigrants in a Western environment.

Wheel-Legged Robotic Limb to Assist Human With Load Carriage: An Application For Environmental Disinfection During COVID-19

During COVID-19, with a heavy sprayer filled with disinfectant, the risk of infection for epidemic prevention personnel has been increased by long-term environmental disinfection. In order to reduce the burden and save energy of human, this letter proposed a Wheel-Legged Robotic Limb (WRL) for the carriers. The mass of WRL is only 1.77 kg. The WRL has one rigid robotic limb located below the sprayer, which can provide active supporting force for the sprayer. The WRL adopts force closed-loop control method to ensure the system provide an expected supporting force. The system performance was evaluated including standing and walking at 5 km/h, under three experimental conditions included: 1) with a sprayer, 19.41 kg (SPRAYER), 2) with the powered WRL, 22.18 kg (WRL_ON), and 3) with the unpowered WRL, 22.18 kg (WRL_OFF). When the supporting force is set as 80 N, the experimental results show that the WRL_ON condition has reduced the vertical load force on the human, the vertical ground reaction force of human feet, and the metabolic power by 41.28%, 8.03%, and 17.46% during standing, and also reduced by 32.29%, 8.08% and 18.92% during walking, compared to SPRAYERcondition, respectively.

The effects of incremental changes in rucksack load on lower extremity joint Kinetic patterns during ruck marching

Injuries are often attributed to ruck marching. Therefore, it is important to examine how load carriage influences gait mechanics. The purpose of this study was to examine how subtle changes in rucksack load influence joint torque patterns during marching. Fourteen Army ROTC cadets marched with light, moderate, and heavy rucksack loads. Kinetic and kinematic data were recorded via an instrumented treadmill and motion capture system and principal component analysis was used to analyse the joint torque waveforms. Cadets exhibited moderate-large increases in knee extension torques during early stance (effect sizes ≥0.45) and small-moderate increases in ankle plantarflexion torques during push off (effect sizes ≥0.23) with each incremental increase in rucksack load. The lighter load also resulted in lower hip extension torques during early stance and flexion torques during late stance, vs. the moderate and heavier loads (effect sizes ≥0.23). It appears that subtle changes in rucksack load influence marching mechanics. Practitioner Summary: The purpose of this study was to examine how relatively subtle changes in rucksack load influence marching mechanics. Army ROTC cadets marched with relatively light, moderate, and heavy rucksack loads. Our results indicate that even subtle changes in rucksack load influence joint torque patterns of the hip, knee, and ankle. Abbreviations: ROTC: reserve officer training corps; RoF: rating-of-fatigue; PC: principal component; ICC: intraclass correlation coefficient; ES: effect size

Mining machines elements packing and securing on platform container

The scientific purpose of this paper was to analyse the problem related to intermodal transportation of mining components packed in containers or other cargo transport units coupled with the problem of its proper securing. In this article, the issue of exposing the load to the effects of inertia forces which might cause unintentional movement is presented. The methods of securing the heavy load in cargo transport units are reviewed in the context of cargo immobilisation possibilities while reducing the load sensitivity to mechanical forces. The research part of this article presents the methods of packing and securing an atypical load, which is a part of a mining machine weighing 18t. This paper presents the results of calculations of inertia forces acting on the transported cargo, packed on a container platform. Based on the results, the cross fixing method was selected to secure the cargo and further decisions were made on the type and quantity of conveyor lashings necessary for the safe and correct carriage of the atypical load.

Effects of modern military backpack loads on walking speed and cardiometabolic responses of US Army Soldiers

IntroductionMilitary leaders must understand how modern military equipment loads affect trade-offs between movement speed and physiological strain to optimize pacing strategies. PurposeTo evaluate the effects of load carried in a recently developed military backpack on the walking speed and cardiometabolic responses of dismounted warfighters. MethodsFifteen soldiers (1 woman, 14 men; age, 22 ± 2 years; height, 173 ± 7 cm; body mass (BM), 73 ± 10 kg) completed incremental walking tests with four external load conditions (0, 22, 44, or 66% BM) using the US Army's newest backpack: the Modular Lightweight Load-Carrying Equipment 4000 (MOLLE 4000). Oxygen uptake (V̇O2) and heart rate (HR) were evaluated relative to maximal values (V̇O2max and HRmax respectively). Testing ceased when participants completed the highest tested speed (1.97 m s−1), exceeded a respiratory exchange ratio (RER) of 1.00, or reached volitional exhaustion. ResultsPeak speed significantly decreased (p < 0.03) with successively heavier loads (0% BM, 1.95 ± 0.06 m s−1; 22% BM, 1.87 ± 0.10 m s−1; 44% BM, 1.69 ± 0.13 m s−1; 66% BM, 1.48 ± 0.13 m s−1). Peak V̇O2 was significantly lower (p < 0.01) with 0% BM (47 ± 5% V̇O2max) than each load (22% BM, 58 ± 8% V̇O2max; 44% BM, 63 ± 10% V̇O2max; 66% BM, 61 ± 11% V̇O2max). Peak HR was significantly lower (p < 0.01) with 0% BM (71 ± 5% HRmax) versus each load (22% BM, 83 ± 6% HRmax; 44% BM, 87 ± 6% HRmax; 66% BM, 88 ± 6% HRmax). ConclusionOverburdened warfighters suffer severe impairments in walking speed even when carrying recently developed military load carriage equipment. Our results suggest that the relative work intensity of heavy load carriage may be better described when expressed relative to HRmax versus V̇O2max.

Spatiotemporal and Kinematic Comparisons Between Anthropometrically Paired Male and Female Soldiers While Walking With Heavy Loads.

Limited work comparing the effect of heavier carried loads (greater than 30 kg) between men and women has attributed observed differences to sex with the possibility that anthropometric differences may have contributed to those discrepancies. With the recent decision permitting women to enter Combat Arms roles, knowledge of sex-based differences in gait response to load carriage is more operationally relevant, as military loads are absolute and not relative to body weight. The purpose of this study was to describe differences in gait parameters at light to heavy loads between anthropometrically similar male and female soldiers. Eight female and 8 male soldiers, frequency-matched (1-to-1) on height (±0.54 cm) and mass (±0.52 kg), walked at 1.34 m∙s-1 for 10-min bouts on a level treadmill while unloaded (BM) and then carrying randomized vest-borne loads of 15, 35, and 55 kg. Spatiotemporal and kinematic data were collected for 30 s after 5 min. Two-way repeated measures analyses of variance were conducted to compare the gait parameter variables between sexes at each load. As load increased, overall, the percent double support increased, step frequency increased, stride length decreased, hip and ankle range of motion (ROM) increased, and vertical center of mass (COM) displacement increased. Sex-based significant differences were observed in knee ROM and mediolateral COM displacement. Among the male participants, knee ROM increased significantly for all loads greater than BM. For mediolateral COM displacement, male remained constant as load increased, whereas female values decreased between BM and 35 kg. Spatiotemporal and kinematic differences in gait parameters were primarily because of increases in load magnitude. The observed sex-related differences with increasing loads suggest that women may require a more stable gait to support the additional load carried.

Effects of body size and load carriage on lower-extremity biomechanical responses in healthy women

BackgroundMusculoskeletal injuries, such as stress fractures, are the single most important medical impediment to military readiness in the U.S. Army. While multiple studies have established race- and sex-based risks associated with a stress fracture, the role of certain physical characteristics, such as body size, on stress-fracture risk is less conclusive.MethodsIn this study, we investigated the effects of body size and load carriage on lower-extremity joint mechanics, tibial strain, and tibial stress-fracture risk in women. Using individualized musculoskeletal-finite-element-models of 21 women of short, medium, and tall statures (n = 7 in each group), we computed the joint mechanics and tibial strains while running on a treadmill at 3.0 m/s without and with a load of 11.3 or 22.7 kg. We also estimated the stress-fracture risk using a probabilistic model of bone damage, repair, and adaptation.ResultsUnder all load conditions, the peak plantarflexion moment for tall women was higher than those in short women (p < 0.05). However, regardless of the load condition, we did not observe differences in the strains and the stress-fracture risk between the stature groups. When compared to the no-load condition, a 22.7-kg load increased the peak hip extension and flexion moments for all stature groups (p < 0.05). However, when compared to the no-load condition, the 22.7-kg load increased the strains and the stress-fracture risk in short and medium women (p < 0.05), but not in tall women.ConclusionThese results show that women of different statures adjust their gait mechanisms differently when running with external load. This study can educate the development of new strategies to help reduce the risk of musculoskeletal injuries in women while running with external load.

A biomechanical study of load carriage by two paired subjects in response to increased load mass

The biomechanics of load carriage has been studied extensively with regards to single individuals, yet not so much with regards to collective transport. We investigated the biomechanics of walking in 10 paired individuals carrying a load that represented 20%, 30%, or 40% of the aggregated body-masses. We computed the energy recovery rate at the center of mass of the system consisting of the two individuals plus the carried load in order to test to what extent the pendulum-like behavior and the economy of the gait were affected. Joint torque was also computed to investigate the intra- and inter-subject strategies occurring in response to this. The ability of the subjects to move the whole system like a pendulum appeared rendered obvious through shortened step length and lowered vertical displacements at the center of mass of the system, while energy recovery rate and total mechanical energy remained constant. In parallel, an asymmetry of joint moment vertical amplitude and coupling among individuals in all pairs suggested the emergence of a leader/follower schema. Beyond the 30% threshold of increased load mass, the constraints at the joint level were balanced among individuals leading to a degraded pendulum-like behavior.

Graded exercise test with or without load carriage similarly measures maximal oxygen uptake in young males and females.

The aim of this was to compare the effects of the graded exercise test (GXT) with or without load carriage on maximal oxygen uptake () heart rate (HR), and expired ventilation () and blood lactate in young healthy males and females. The study included ten females (age:20.2±0.7 yrs) and ten males (age:19.5±0.7 yrs) who performed the modified Bruce protocol at five load conditions; unloaded, 5, 10, 15, and 20% of body weight (BW) (kg). All the tests were performed in random order, at least 48 hours apart. During the GXTs, HR, , , workload and test duration were recorded and blood lactate concentration was measured before and immediately after the GXTs. remained unchanged during the GXTs in load and unloaded conditions for both sexes (p>0.05). Test duration was significantly less in females during the GXT with 15% BW (15.9±0.51 min vs. 18.1±1.14 min; p = 0.014) and 20% BW load carriage (15.2±0.75 min vs. 18.1±1.14 min; p = 0.020), compared to the unloaded GXT. Males showed significant decrease in the test duration during the GXT with load 15% BW (20.5±0.53 min vs. 22.8±0.61 min; p = 0.047) and with 20% BW (19.6±0.42 min vs. 22.8±0.71 min; p = 0.004), compared to the GXT with 5% BW. statistically decreased in female subjects only at 15% BW compared to 20% BW (15% BW = 77.9 ± 10.5 L/min vs. 15% BW = 72.0 ± 10.9 L/min; p = 0.045). There was no difference observed in maximal HR and blood lactate concentration between the GXTs in load and unloaded conditions. This study indicates that no matter the load % used during the GXT, , but not total exercise time, remains the same in young males and females.

The Influence of Carrying Anterior Load on the Sagittal and Frontal Plane Kinematics of Lower Extremities during Stair Ascending.

Background: Anterior load carriage is a one of the commonly performed activities in some industries. Stair climbing while carrying anterior load significantly alters different biomechanical mechanisms that can potentially affect the musculoskeletal function of the lower extremities.Objective: The study aims to assess the effect of carrying an anterior load (20% of body weight) on lower extremity kinematics during the kinematical phases of stairs ascent (weight acceptance, pull up, forward continuance, and swing phase).Material and Methods: In this experimental study, data were collected through the use of a custom made wooden staircase and OPtiTrack motion capture system was composed of 12 infrared cameras and a per modeled reflective marker set. Sixteen female college students volunteered to conduct two tasks of ascending stairs with and without an anterior load of approximately 20% of their body weight. The collected frontal and sagittal plane lower extremity joint angles were calculated using MATLAB software (version R2015a). Statistical comparison between the two study tasks was made using IBM SPSS Statistics software (version 25.0; SPSS Inc., Chicago, IL, USA). Results: Based on the results, there is significant difference (p-value < 0.05) between the two study tasks during ascending stair phases in all three sagittal plan lower extremity joint angles. Conclusion: Anterior load carried during stair ascent causes participants to depend more on the hip joint (higher flexion angles) compared to stair ascent without loads, which may increase the risk of falls and injuries, and the importance of muscle-strengthening activities and highlight the use of appropriate technique during load carriage.

A Thorax Marker Set Model to Analyse the Kinematics of Walking Without the Need to Place Markers on the Back.

Previous thorax models have been proposed for gait analysis, however these require markers to be placed on the back. This presents a limitation in the kinematic analysis of the thorax under load carriage conditions. This study evaluated the validity and reliability of a thorax marker set that does not require markers to be placed on the back (HubemaLab model) when compared to 3 previously published marker set models. 17 young adults were evaluated while walking at their self-selected speed. A 12 camera motion capture system was used to acquire the marker position data which was then processed using the respective models using Visual-3D. The level of agreement for the flexion/extension peak, right/left lateral peak and right/left rotation peak of the thorax angle and angular velocity; together with the range of motion and thorax angular velocities in the three planes was found between each thorax marker set, while the reliability was measured using the intraclass correlation coefficient. The ICC results for the thorax angle ROM and the range of thorax angular velocity between the HubemaLab model and the other models showed excellent to good reliability in all three planes. While the ICCs for the peak flexion/extension, peak right/left lateral flexion and peak right/left rotation showed excellent to moderate reliability in all three planes. The new model could be potentially valuable for kinematic gait analysis under load carriage conditions which obscure markers placed on the back.

Increased velocity at VO2max and load carriage performance in army ROTC cadets: prescription using the critical velocity concept

The purpose of this study was to evaluate the effects of using the critical velocity (CV) concept to prescribe two separate high-intensity interval training (HIT) exercise programs aimed at enhancing CV and load carriage performance. 20 young adult participants (male = 15, female = 5) underwent a 4-week training period where they exercised 2 dwk−1. Participants were randomly assigned into two groups: (1) HIT or (2) Load Carriage-HIT (LCHIT). Pre- and post-training assessments included running 3-minute All-Out Test (3MT) to determine critical velocity (CV) and distance prime (D′) and two load carriage tasks (400 and 3200 m). There were significant increases in CV (p = 0.005) and velocity at V˙ O2max (v V˙ O2max) (p = 0.037) among the sample but not between training groups. Improvements were observed in 3200 m load carriage performance time (p < 0.001) with a 9.8 and 5.4% decrease in the LCHIT and HIT groups, respectively. Practitioner summary: Critical velocity has shown efficacy as a marker for performance in tactical populations. With the addition of load carriage, there is a reduction in the individual’s CV. The CV-concept-prescribed exercises (HIT and LCHIT) 2 days per week for 4 weeks showed improvements in CV, v V˙ O2max and load carriage performance. The use of the CV concept provides a method to prescribe HIT to increase running and load carriage performances in tactical populations.

Dynamics of locomotion in the seed harvesting antMessor barbarus:effect of individual body mass and transported load mass

Ants are well-known for their amazing load carriage performances. Yet, the biomechanics of locomotion during load transport in these insects has so far been poorly investigated. Here, we present a study of the biomechanics of unloaded and loaded locomotion in the polymorphic seed-harvesting ant Messor barbarus (Linnaeus, 1767). This species is characterized by a strong intra-colonial size polymorphism with allometric relationships between the different body parts of the workers. In particular, big ants have much larger heads relative to their size than small ants. Their center of mass is thus shifted forward and even more so when they are carrying a load in their mandibles. We investigated the dynamics of the ant center of mass during unloaded and loaded locomotion. We found that during both unloaded and loaded locomotion, the kinetic energy and gravitational potential energy of the ant center of mass are in phase, which is in agreement with what has been described by other authors as a grounded-running gait. During unloaded locomotion, small and big ants do not display the same posture. However, they expend the same amount of mechanical energy to raise and accelerate their center of mass per unit of distance and per unit of body mass. While carrying a load, compared to the unloaded situation, ants seem to modify their locomotion gradually with increasing load mass. Therefore, loaded and unloaded locomotion do not involve discrete types of gait. Moreover, small ants carrying small loads expend less mechanical energy per unit of distance and per unit of body mass and their locomotion thus seem more mechanically efficient.

Physiological interactions with personal-protective clothing, physically demanding work and global warming: An Asia-Pacific perspective.

The Asia-Pacific contains over half of the world's population, 21 countries have a Gross Domestic Product <25% of the world's largest economy, many countries have tropical climates and all suffer the impact of global warming. That 'perfect storm' exacerbates the risk of occupational heat illness, yet first responders must perform physically demanding work wearing personal-protective clothing and equipment. Unfortunately, the Eurocentric emphasis of past research has sometimes reduced its applicability to other ethnic groups. To redress that imbalance, relevant contemporary research has been reviewed, to which has been added information applicable to people of Asian, Melanesian and Polynesian ancestry. An epidemiological triad is used to identify the causal agents and host factors of work intolerance within hot-humid climates, commencing with the size dependency of resting metabolism and heat production accompanying load carriage, followed by a progression from the impact of single-layered clothing through to encapsulating ensembles. A morphological hypothesis is presented to account for inter-individual differences in heat production and heat loss, which seems to explain apparent ethnic- and gender-related differences in thermoregulation, at least within thermally compensable states. The mechanisms underlying work intolerance, cardiovascular insufficiency and heat illness are reviewed, along with epidemiological data from the Asia-Pacific. Finally, evidence-based preventative and treatment strategies are presented and updated concerning moisture-management fabrics and barriers, dehydration, pre- and post-exercise cooling, and heat adaptation. An extensive reference list is provided, with >25 recommendations enabling physiologists, occupational health specialists, policy makers, purchasing officers and manufacturers to rapidly extract interpretative outcomes pertinent to the Asia-Pacific.

Why highly compliant poles are not energetically beneficial during running: Evidence from an optimization-based biped model

Springy poles are a unique load-carrying tool and inspire novel designs of other load-carrying systems. Previous experiments have shown that highly compliant poles with a natural frequency lower than step frequency are more economical than rigid poles during load carriage in walking and this was successfully explained in later modeling studies. However, an energetic benefit was not observed during running with highly compliant poles. We speculate that gait type (running versus walking) may be a factor accounting for the different observations. An optimization-based biped model is adopted to predict the energy cost of load carriage with poles during running, with the parameters from previous experimental studies. The predicted load motion and load-body interaction force agree well with experimental measurements. Compared to running with rigid poles, the highly compliant pole results in reduced peak ground reaction force, longer stance phase duration, and higher energy cost. The changes in running energetics are further found to depend on the natural frequency of the load-pole system relative to the step frequency, but with an opposite trend compared to the changes in walking energetics during pole carriage. Highly compliant poles cost more energy than rigid poles during running, while stiffer poles with a higher natural frequency may offer energetic benefits. This study indicates that the fundamental difference in gait type has a profound influence on the energetic performance of load-carrying devices and this should be taken into consideration in future device designs.

Using Machine Learning and Wearable Inertial Sensor Data for the Classification of Fractal Gait Patterns in Women and Men During Load Carriage

Ambulating while carrying a mission specific load is one of the most frequently executed occupational tasks for the military, especially for individuals in combat roles. Prolonged ambulation is a naturally dynamic and complex process, characterized by highly multi-dimensional interactions within the gait mechanics of the lower extremity. Recent wearable sensors studies, like inertial measurement unit (IMU)-related gait studies have demonstrated that machine learning (MLN) algorithms and fractal analysis can successfully discriminate between classes, such as movement patterns, injury, age and sex. This study attempts to classify fractal gait patterns of women and men using IMU-based signal data obtained from accelerometer, gyroscope and magnetometer during a 2 km loaded (20 kg) march. Random Forest (RF) MLN algorithm was used to generate a model that can measure the accuracy and identify the importance of IMU-based signal-related fractal variables. A total of 18 variables were calculated using 2 fractal methods, detrended fluctuation analysis (DFA) and wavelet transform-based power spectral density (PSD), from 3 IMU-based signals in their 3 axes (medial-lateral, vertical and anterior-posterior). A total of 33 healthy adults (17 men [26.7±5.9 years] and 16 women [25.2±4.5 years]) volunteered for this study. A 9-axis IMU sensor was attached to each participant at each of the following locations: feet, shanks, thighs and lumbar spine. An independent training-testing approach, called one-vs-one ( i.e., variables from one IMU-based signal were trained and tested using another IMU-based signal) was applied to determine the classification accuracy ( i.e., similarities between IMUs) and variable importance (score ranges: 0.0-1.0) measures. These values were then used to select the variables that best independently describe the rank in classification margin. The results from each IMU sensor placement based on the fractal values showed ‘moderate’ accuracy (50-75%), with the exception of two cases: the left shank yielded ‘good’ accuracy (80.1%) compared with the right shank, and the right thigh generated ‘poor’ accuracy (48.9%) compared with the left foot. No IMU location showed excellent accuracy (>90%). The results indicate that each IMU placement location has their own fractal patterns that are not similar to another IMU location in terms of sex classification. The analysis of the variable importance in the classification margin showed that most of the PSD resulted variables were classified as ‘most important’ compared with the DFA resulted variables. IMU sensors, and the associated analyses, could be used during military load carriage to evaluate changes in gait resulting from injury, fatigue or overtraining.