Effects of prolonged load carriage on ground reaction forces, lower limb kinematics and spatio-temporal parameters in female recreational hikers

The effect of load carriage on female recreational hikers has received little attention. This study collected lower limb sagittal plane kinematic, spatio-temporal and ground reaction force (GRF) data from 15 female hikers carrying four loads (0%, 20%, 30% and 40% body weight (BW)) over 8 km. Increasing load resulted in a proportional increase in GRF up to 30% BW, increased stance time, and greater mediolateral impulse with 30% and 40% BW. Also seen were decreased velocity and cadence and increased double support and knee flexion when carrying load compared to no load. Increased distance resulted in increased knee flexion and ankle plantar flexion at initial foot-ground contact. It was concluded that, as load mass and distance increased, female hikers modified their gait to attenuate the lower limb impact forces. When carrying 30% and 40% BW loads, however, the changes aimed at attenuating the higher GRF may result in a less stable gait. PRACTITIONER SUMMARY: Limited research has investigated the biomechanical responses of female recreational hikers to prolonged load carriage. This study provides a better understanding of the effects of increasing load on lower limb kinematics, spatio-temporal parameters and the GRF generated by female hikers during prolonged load carriage. The results have implications for the development of load carriage guidelines to minimise the risk of injury to females who carry backpacks and to improve performance for this population.     

Effects of military load carriage on kinematics of gait

Manual load carriage is a universal activity and an inevitable part of the daily schedule of a soldier. Indian Infantry soldiers carry loads on the waist, back, shoulders and in the hands for a marching order. There is no reported study on the effects of load on gait in this population. It is important to evaluate their kinematic responses to existing load carriage operations and to provide guidelines towards the future design of heavy military backpacks (BPs) for optimising soldiers' performance. Kinematic changes of gait parameters in healthy male infantry soldiers whilst carrying no load (NL) and military loads of 4.2–17.5 kg (6.5–27.2% body weight) were investigated. All comparisons were conducted at a self-selected speed. Soldier characteristics were: mean (SD) age 23.3 (2.6) years; height 172.0 (3.8) cm; weight 64.3 (7.4) kg. Walk trials were collected using a 3-D Motion Analysis System. Results were subjected to one-way ANOVA followed by Dunnett post hoc test. There were increases in step length, stride length, cadence and midstance with the addition of a load compared to NL. These findings were resultant of an adaptive phenomenon within the individual to counterbalance load effect along with changes in speed. Ankle and hip ranges of motion (ROM) were significant. The ankle was more dorsiflexed, the knee and hip were more flexed during foot strike and helped in absorption of the load. The trunk showed more forward leaning with the addition of a load to adjust the centre of mass of the body and BP system back to the NL condition. Significant increases in ankle and hip ROM and trunk forward inclination (≥10°) with lighter loads, such as a BP (10.7 kg), BP with rifle (14.9 kg) and BP with a light machine gun (17.5 kg), may cause joint injuries. It is concluded that the existing BP needs design improvisation specifically for use in low intensity conflict environments.

Statement of Relevance:The present study evaluates spatial, temporal and angular changes at trunk and limb joints during military load carriage of relatively lighter magnitude. Studies on similar aspects on the specific population are limited. These data can be used for optimising load carriage and designing ensembles, especially a heavy BP, for military operations.     

Does load position affect gait and subjective responses of females during load carriage?

Recreational hikers carry heavy loads while often walking long distances over uneven terrain. Previous studies have suggested that not only the load mass but also the position of the load may influence load carriage. The purpose of this study was to determine the effect of vertical load position on gait and subjective responses of female recreational hikers. Fifteen experienced female hikers walked for 2 km over a simulated hiking trail carrying 30% BW in three vertical load positions (high, medium and low). Lower limb and trunk kinematic, electromyography (EMG) and ground reaction force (GRF) data were collected together with heart rate (HR), ratings of perceived exertion (RPE) and discomfort measures. Although HR, RPE and discomfort measures were not able to discern statistical differences between load positions, the high load position was the most preferred by participants. The high load position also resulted in a more upright posture (p < 0.001), decreased gastrocnemius integrated EMG compared to the medium (p = 0.005) and low load positions (p = 0.02) and a higher first peak deceleration vertical GRF compared to the low load position (p = 0.011). However, the absolute differences were small and unlikely to be functionally relevant in load carriage studies. Based on the findings of this study, a high, medium or low load position cannot be preferentially recommended for healthy, experienced, female hikers carrying 30% BW.     

Effects of backpack load and positioning on nonlinear gait features in young adults

Overloaded backpacks can cause changes in posture and gait dynamic balance. Therefore, the aim of this study was to assess gait regularity and local dynamic stability in young adults as they carried a backpack in different positions, and with different loads. Twenty-one healthy young adults participated in the study, carrying a backpack that was loaded with 10 and 20% of their body weight (BW). The participants walked on a level treadmill at their preferred walking speeds for 4 min under different conditions of backpack load and position (i.e. with backpack positioned back bilaterally, back unilaterally, frontally or without a backpack). Results indicate that backpack load and positioning significantly influence gait stability and regularity, with the exception of the 10% BW bilateral back position. Therefore, the recommended safe load for school-age children and adolescents (10% of BW) should also be considered for young adults.

Practitioner summary: Increase in load results in changes in posture, muscle activity and gait parameters, so we investigated the gait adaptations related to regularity and stability. Conditions with high backpack loads significantly influenced gait stability and regularity in a position-dependent manner, except for 10% body weight bilateral back position.     

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.     

Physiological and biochemical responses during incremental uphill load carriage

The present study aimed to examine the effect of carrying different magnitudes of load on the changes and relationships of salivary Immunoglobulin A (IgA) and cortisol concentrations and the physiological parameters. Twelve Indian soldiers performed an intense uphill treadmill walking at two speeds viz. 2.5 km h⁻¹ and 4 km h⁻¹ without any load and carrying 10.7 kg, 17 kg and 21.4 kg loads for 36 min. Salivary IgA concentration relative to total protein decreased significantly after each exercise session and cortisol concentration increased concomitantly with physiological variables e.g. heart rate (HR), oxygen consumption (VO₂), minute ventilation (VE) and energy expenditure (EE). An inverse correlation (P < 0.05) was observed between IgA with HR for all the conditions except when the participants walked at 4 km h⁻¹ carrying 17 kg and 21.4 kg load. The degree and type of physiological and biochemical responses may help in designing combat training, operations and developing preventive strategies of military personnel involving intense exercise.Relevance to industry: Walking with load in incremental uphill terrain is highly stressful and fatiguing. Results of the present study will help in designing training schedules for maintaining the optimal fitness of an individual during uphill walking with loads in different speeds.     

Optimization of load carriage at desert environment

The present study was undertaken to assess the effect of different magnitudes of load on physiological responses of soldiers in desert terrain and also to estimate an optimum load that can be carried comfortably at specific walking speed. Nine infantry male soldiers of SHAPE-I standard with age 25.22 ± 1.02 years, height 170.78 ± 0.95 cm and weight 66.56 ± 2.38 Kg volunteered in this study. All participants were marched at speed of 6.13 ± 0.40 Km h⁻¹ in desert terrain with 10.7 Kg (16.07% BW) and 21.4 Kg (32.15% BW) load and without load. Heart rate (HR), respiratory frequency (RF), oxygen consumption (VO₂), minute ventilation (VE), energy expenditure (EE) and relative work load (RWL) were recorded by using K4b² system. During carrying of 10.7 Kg load HR, VO₂, EE, RF, VE and RWL (%VO₂max) were increased 13.88, 18.20, 20.16, 7.86, 19.30 and 23.71% respectively in comparison to no load. Similarly, during 21.4 Kg load, physiological responses viz.; HR, VO₂, EE, RF, VE and RWL (%VO₂max) were increased 24.84, 36.98, 33.68, 21.24, 38.25 and 40.64% respectively in comparison to no load. The observation of this study stated that 6.27 Kg (9.42%BW, 50% RWL), 13.7 Kg (20.58%BW, 60%RWL) and 24.86 Kg (37.35%BW, 75% RWL) can be recommended for 8 h, 2 h and for 30 min respectively.Relevance to industryMost of the countries do not have their own database for load carriage in specific environmental conditions. Result of this study will be helpful to the similar kind of population working under specified conditions.     

Effects of different loads and carrying systems on selected biomechanical parameters describing walking gait

The effects of two different systems on selected biomechanical parameters of walking gait, while carrying loads of varying magnitude, were investigated.

Ten healthy males who were not regularly engaged in carrying tasks walked a distance of 20 m for ten trials for each of the following five conditions: (i) normal walking without any external load; (ii) 20% and (iii) 40% body weight carried using a backpack system; and (iv) 20% and (v) 40% body weight carried using a doublepack system which distributed the load equally between the front and back of the subjects. The experimental set-up consisted of a Kistler force platform interfaced to a Tektronix 4051 Graphic Calculator, two super 8 mm movie cameras and a photoelectric timing system. Force data (417 Hz) were obtained for ten trials along with side- and rear-view film data (100 fps) for three of the trials for each of the subject conditions. In addition, selected aspects of foot-position data were acquired from a minimum of six footprints from one trial for each subject condition. Walking speed was controlled at 4·5 ± 0·3km/h. Parameters describing the temporal relationship of the gait pattern and values describing the spatial relationship of foot position were evaluated. Selected variables describing the components of the ground-reaction-force-time curves were also examined. Finally, selected kinematic and kinetic parameters were evaluated for four functional subphases of the support period.

Comparisons using a one-way ANOVA with repeated measures were conducted to examine differences between parameters describing the load-carrying conditions and normal gait. Results from the analysis revealed that both the light and heavy loads substantially modified the normal walking gait pattern. Interactions between the load conditions and carrying systems were tested using separate two-way ANOVA with repeated measures. Significant ordinal interactions as well as significant main effects were found between the two carrying systems for some parameters, suggesting that the doublepack system was more effective than the conventional backpack system, especially for carrying the heavy load.     

Evaluation of the effect of backpack load and position during standing and walking using biomechanical,physiological and subjective measures

Recommendations on backpack loading advice restricting the load to 10% of body weight and carrying the load high on the spine. The effects of increasing load (0%–5%–10%–15% of body weight) and changing the placement of the load on the spine, thoracic vs. lumbar placement, during standing and gait were analysed in 20 college-aged students by studying physiological, biomechanical and subjective data. Significant changes were: (1) increased thorax flexion; (2) reduced activity of M. erector spinae vs. increased activation of abdominals; (3) increased heart rate and Borg scores for the heaviest loads. A trend towards increased spinal flexion, reduced pelvic anteversion and rectus abdominis muscle activity was observed for the lumbar placement. The subjective scores indicate a preference for the lumbar placement. These findings suggest that carrying loads of 10% of body weight and above should be avoided, since these loads induce significant changes in electromyography, kinematics and subjective scores. Conclusions on the benefits of the thoracic placement for backpack loads could not be drawn based on the parameter set studied.     

Effect of load mass on posture, heart rate and subjective responses of recreational female hikers to prolonged load carriage

Load carriage has been associated with a risk of upper and lower limb musculoskeletal disorders with women suffering significantly higher injury rates than their male counterparts. Despite this injury risk, there are limited evidence-based guidelines for recreational hikers, particularly female recreational hikers, regarding safe backpack loads. The purpose of the present study was to determine how variations in load mass affected the heart rate, posture and subjective responses of women during prolonged walking to provide evidence for a load mass limit for female recreational hikers. Heart rate (HR), posture and ratings of perceived exertion (RPE) and discomfort were collected for 15 female experienced recreational hikers (22.3 ± 3.9 years) while they hiked for 8 km at a self-selected pace under four different load conditions (0%, 20%, 30% and 40% of body weight (BW)). Although HR was not significantly affected by load mass or walking distance, increasing load mass and distance significantly affected posture, RPE and discomfort of the upper body. Carrying a 20% BW load induced significant changes in trunk posture, RPE and reported shoulder discomfort compared to the unloaded condition. The 20% BW load also resulted in a mean RPE rating of ‘fairly light’, which increased to ‘hard’ when carrying a 40% BW load. As load carriage distance increased participants reported significantly increased shoulder, neck and upper back discomfort. Based on the changes to posture, self-reported exertion and discomfort when carrying loads of 20%, 30% and 40% BW over 8 km, it was concluded that a backpack load limit of 30% BW should be recommended for female recreational hikers during prolonged walking.     

Evaluation of the effect of backpack load and position during standing and walking using biomechanical, physiological and subjective measures

Recommendations on backpack loading advice restricting the load to 10% of body weight and carrying the load high on the spine. The effects of increasing load (0%-5%-10%-15% of body weight) and changing the placement of the load on the spine, thoracic vs. lumbar placement, during standing and gait were analysed in 20 college-aged students by studying physiological, biomechanical and subjective data. Significant changes were: (1) increased thorax flexion; (2) reduced activity of M. erector spinae vs. increased activation of abdominals; (3) increased heart rate and Borg scores for the heaviest loads. A trend towards increased spinal flexion, reduced pelvic anteversion and rectus abdominis muscle activity was observed for the lumbar placement. The subjective scores indicate a preference for the lumbar placement. These findings suggest that carrying loads of 10% of body weight and above should be avoided, since these loads induce significant changes in electromyography, kinematics and subjective scores. Conclusions on the benefits of the thoracic placement for backpack loads could not be drawn based on the parameter set studied.     

The effect of military load carriage on 3-D lower limb kinematics and spatiotemporal parameters

The 3-D gait analysis of military load carriage is not well represented, if at all, within the available literature. This study collected 3-D lower limb kinematics and spatiotemporal parameters in order to assess the subsequent impact of carrying loads in a backpack of up to 32 kg. Results showed the addition of load significantly decreased the range of motion of flexion/extension of the knee and pelvic rotation. Also seen were increases in adduction/abduction and rotation of the hip and pelvis tilt. No changes to ankle kinematics were observed. Alterations to the spatiotemporal parameters of gait were also of considerable interest, namely, an increase in double support and a decrease in preferred stride length as carried load increased. Analysing kinematics during military or recreational load carriage broadens the knowledge regarding the development of exercise-related injuries, while helping to inform the human-centred design process for future load carrying systems. The importance of this study is that limited available research has investigated 3-D lower limb joint kinematics when carrying loads.     

Application of wearable sensors for human gait analysis using fuzzy computational algorithm

The authors have developed and tested a wearable inertial sensor system for the acquisition of gait features. The sensors were placed on anatomical segments of the lower limb: foot, shank, thigh, and hip, and the motion data were then captured in conjunction with 3D ground reaction forces (GRFs). The method of relational matrix was applied to develop a rule-based system, an intelligent fuzzy computational algorithm. The rule-based system provides a feature matrix model representing the strength of association or interaction amongst the elements of the gait functions (limb-segments accelerations and GRFs) throughout the gait cycle. A comparison between the reference rule-based data and an input test data was evaluated using a fuzzy similarity algorithm. This system was tested and evaluated using two subject groups: 10 healthy subjects were recruited to establish the reference fuzzy rule-base, and 4 relapsing remitting multiple sclerosis subjects were used as an input test data; and the grade of similarity between them was evaluated. This similarity provides a quantitative assessment of mobility state of the impaired subject. This algorithmic tool may be helpful to the clinician in the identification of pathological gait impairments, prescribe treatment, and assess the improvements in response to therapeutic intervention.     

Impact of ballistic body armour and load carriage on walking patterns and perceived comfort

This study investigated the impact of weight magnitude and distribution of body armour and carrying loads on military personnel's walking patterns and comfort perceptions. Spatio-temporal parameters of walking, plantar pressure and contact area were measured while seven healthy male right-handed military students wore seven different garments of varying weight (0.06, 9, 18 and 27 kg) and load distribution (balanced and unbalanced, on the front and back torso). Higher weight increased the foot contact time with the floor. In particular, weight placement on the non-dominant side of the front torso resulted in the greatest stance phase and double support. Increased plantar pressure and contact area observed during heavier loads entail increased impact forces, which can cause overuse injuries and foot blisters. Participants reported increasingly disagreeable pressure and strain in the shoulder, neck and lower back during heavier weight conditions and unnatural walking while wearing unbalanced weight distributed loads. This study shows the potentially synergistic impact of wearing body armour vest with differential loads on body movement and comfort perception.

Practitioner Summary: This study found that soldiers should balance loads, avoiding load placement on the non-dominant side front torso, thus minimising mobility restriction and potential injury risk. Implications for armour vest design modifications can also be found in the results.     

Effect of backpack load on the head,cervical spine and shoulder postures in children during gait termination

Twelve boys with an average age of 9.9 years were instructed to carry backpacks that weighed 0%, 10% and 15% of their body weights (BWs) to complete planned and unplanned gait termination experiments. The craniohorizontal, craniovertebral and sagittal shoulder posture angles at the sagittal plane as well as the anterior head alignment and coronal shoulder posture angles at the coronal plane were analysed. Results revealed significantly smaller craniohorizontal and sagittal shoulder posture angles during planned gait termination and a significantly smaller sagittal shoulder posture angle during unplanned gait termination under loaded conditions compared with those at 0% BW backpacks. Furthermore, the coronal shoulder posture angles at 10% and 15% BW during planned and unplanned gait terminations were significantly larger than those at 0% BW. Therefore, subjects were more likely to have a forward head posture, rounded shoulder posture and increased lateral tilting of the shoulders during gait termination as backpack loads were increased. However, gait termination, whether planned or unplanned, did not elicit a remarkable effect on posture.     

Influence of pressure-relief insoles developed for loaded gait (backpackers and obese people) on plantar pressure distribution and ground reaction forces

The aims of this study were to test the effects of two pressure relief insoles developed for backpackers and obese people on the ground reaction forces (GRF) and plantar pressure peaks during gait; and to compare the GRF and plantar pressures among normal-weight, backpackers, and obese participants. Based on GRF, plantar pressures, and finite element analysis two insoles were manufactured: flat cork-based insole with (i) corkgel in the rearfoot and forefoot (SLS1) and with (ii) poron foam in the great toe and lateral forefoot (SLS2). Gait data were recorded from 21 normal-weight/backpackers and 10 obese participants. The SLS1 did not influence the GRF, but it relieved the pressure peaks for both backpackers and obese participants. In SLS2 the load acceptance GRF peak was lower; however, it did not reduce the plantar pressure peaks. The GRF and plantar pressure gait pattern were different among the normal-weight, backpackers and obese participants.     

Influence of school bag loads and carrying methods on body strain among young male students

This study examined the influences of schoolbag carrying modes combined with carrying weights on the body posture alterations, muscle activations, and subjective discomfort scores of participants. Twelve male university students were recruited as participants and executed nine test combinations of three carrying methods (2-strap backpack, 1-strap side backpack, and 1-strap crossbody carrying) generally used by Taiwanese young students and three loads (5%, 10%, and 15% of their respective body weights [BWs]). The results revealed that carried load and method significantly affected body posture and trapezius activation. Side backpack carrying should be avoided because of the relatively high lateral shoulder tilt, trunk flexion, right trapezius activation, and low lumbosacral angle observed compared with other two carrying methods. The unbalanced load of side backpack carrying may cause an uneven shoulder posture, thus resulting in extra body strains. Furthermore, carrying loads at 10% of BW was recommended when carrying a 2-strap backpack.Relevance to industryThe daily carriage of a schoolbag or backpack on the musculoskeletal health of young students has been a permanent concern. The findings suggest that carrying a load weighing 15% of BW and using the unbalanced side backpack carrying method should be avoided.     

Biomechanical model for energy consumption in manual load carrying on Indian farms

This study pertains to manually carrying load in Indian farms. Different modes are adopted for carrying farm inputs and farm produce; head, shoulder and back. A biomechanical model was developed and validated to predict metabolic energy consumption for carrying load manually by varying modes, loads and ground inclinations. The model developed incorporated operator, ground inclination and load parameters. Operator parameters included human efficiency, body weight and height of the worker. Load parameters considered were weight of load and mode of load carrying. Experiments on three modes (head, back and shoulder) and three loads (10, 15, 20 kg load) at three slopes (0, 5, 10%) were conducted in a laboratory set up. Twelve farm workers (six males and six females) working in local farms participated in the study. The model closely predicted energy and rest requirement for load carrying in different modes.     

Wearing body armour and backpack loads increase the likelihood of expiratory flow limitation and respiratory muscle fatigue during marching

Abstract

The effect of load carriage on pulmonary function was investigated during a treadmill march of increasing intensity. 24 male infantry soldiers marched on six occasions wearing either: no load, 15?kg, 30?kg, 40?kg or 50?kg. Each loaded configuration included body armour which was worn as battle-fit or loose-fit (40?kg only). FVC and FEV₁ were reduced by 6 to 15% with load. Maximal mouth pressures were reduced post load carriage by up to 11% (inspiratory) and 17% (expiratory). Increased ventilatory demands associated with carrying increased mass were met by increases in breathing frequency (from 3 to 26 breaths·min^?1) with minimal changes to tidal volume. 72% of participants experienced expiratory flow limitation whilst wearing the heaviest load. Loosening the armour had minimal effects on pulmonary function. It was concluded that as mass and exercise intensity are increased, the degree of expiratory flow limitation also increases.

Practitioner Summary: This study investigated the effect of soldier load carriage on pulmonary function, to inform the trade-off between protection and burden. Load carriage caused an inefficient breathing pattern, respiratory muscle fatigue and expiratory flow limitation during marching. These effects were exacerbated by increases in mass carried and march intensity.     

A momentum-based balance controller for humanoid robots on non-level and non-stationary ground

Recent research suggests the importance of controlling rotational dynamics of a humanoid robot in balance maintenance and gait. In this paper, we present a novel balance strategy that controls both linear and angular momentum of the robot. The controller’s objective is defined in terms of the desired momenta, allowing intuitive control of the balancing behavior of the robot. By directly determining the ground reaction force (GRF) and the center of pressure (CoP) at each support foot to realize the desired momenta, this strategy can deal with non-level and non-stationary grounds, as well as different frictional properties at each foot-ground contact. When the robot cannot realize the desired values of linear and angular momenta simultaneously, the controller attributes higher priority to linear momentum at the cost of compromising angular momentum. This creates a large rotation of the upper body, reminiscent of the balancing behavior of humans. We develop a computationally efficient method to optimize GRFs and CoPs at individual foot by sequentially solving two small-scale constrained linear least-squares problems. The balance strategy is demonstrated on a simulated humanoid robot under experiments such as recovery from unknown external pushes and balancing on non-level and moving supports.