Metabolic costs of load carriage with different container sizes

Abstract

Six well-trained male subjects carried boxes of varying box width and weight at varying speeds on a level treadmill until steady-state heart rates were obtained. Analysis of the steady-state data for heart rate and metabolic cost led to development of highly accurate predictor models for both factors. The metabolic-cost model accounted for over 94% of the variance (R²>0·94), and the heart-rate model accounted for over 81% of the variance present (R²>0·81). Evaluation of other models for predicting physiological response to carrying loads found their predictions to differ significantly from the data of the present study.     

Effects of load carriage, load position, and walking speed on energy cost of walking

PURPOSE: The purpose of this study was to examine the effects of load, load position, and walking speed on the energy cost of walking per unit distance (Cw: ml/kg/m). METHODS: Eight young male subjects walked on a treadmill at various speeds with and without load in the hands, on the back, and on the legs. The Cw values were determined from the ratio of 2-min steady-state oxygen consumption (Vo2) above resting value (net Vo2) to the walking speed (v): Cw = net Vo2/v. RESULTS: An energy-saving phenomenon was observed when the load was carried on the back at slower speeds. This phenomenon diminished at faster speeds, particularly when walking faster than 90 m/min. It was also observed when the load was carried in the hands at slower speeds. CONCLUSIONS: These findings partly supported our hypothesis that an energy-saving phenomenon would be observed due to an interaction between rotative torque around the center of body mass and excessive burden on the lower muscles as a function of speed.     

The effect of load distribution within military load carriage systems on the kinetics of human gait

Military personnel carry their equipment in load carriage systems (LCS) which consists of webbing and a Bergen (aka backpack). In scientific terms it is most efficient to carry load as close to the body's centre of mass (CoM) as possible, this has been shown extensively with physiological studies. However, less is known regarding the kinetic effects of load distribution. Twelve experienced load carriers carried four different loads (8, 16, 24 and 32 kg) in three LCS (backpack, standard and AirMesh). The three LCS represented a gradual shift to a more even load distribution around the CoM. Results from the study suggest that shifting the CoM posteriorly by carrying load solely in a backpack significantly reduced the force produced at toe-off, whilst also decreasing stance time at the heavier loads. Conversely, distributing load evenly on the trunk significantly decreased the maximum braking force by 10%. No other interactions between LCS and kinetic parameters were observed. Despite this important findings were established, in particular the effect of heavy load carriage on maximum braking force. Although the total load carried is the major cause of changes to gait patterns, the scientific testing of, and development of, future LCS can modify these risks.     

The effects of load placement on the EMG activity of the low back muscles during load carrying by men and women

An electromyographic (EMG) study of the lumbar paraspinal muscles during load carrying was undertaken in a group of 24 healthy subjects, 12 male and 12 female. Two different magnitude loads (10% and 20% of the subject's body weight) and four different carrying positions were compared with walking without an external load. Results indicated changes in back muscle activity showing a significant interaction between load magnitude and carrying position. Compared to walking without an external load, lumbar paraspinal EMG activity showed slight decreases when loads were carried in a backpack position or in the hand ipsilateral to the muscle. EMG activity contralateral to the hand carrying the load was significantly increased. Significant increases occurred when loads were carried anterior to the chest with the arms and a significant difference was found between male and female subjects for this carrying position. These findings have implications for the selection of carrying methods.     

Schoolbag weight and musculoskeletal symptoms in New Zealand secondary schools

The weight of schoolbags and the prevalence of musculoskeletal symptoms amongst 140 students (70 third form students comprising 35 females and 35 males, and 70 sixth form students comprising 35 females and 35 males) from five New Zealand secondary schools was investigated. Schoolbag weight for third form students (mean age 13.6 years) was 13.2% of their body weight, while for sixth form students (mean age 17.1 years) it was 10.3% of their body weight. These weights may exceed the recommended guideline load limits for adult industrial workers. Musculoskeletal symptoms were reported by 77.1% of the students. Symptoms were most prevalent in the neck, shoulders, upper back and lower back. Although musculoskeletal symptoms are believed to be multifactorial in origin, the carriage of heavy schoolbags is a suspected contributory factor and may represent an overlooked daily physical stress for New Zealand secondary school students.     

Effects of Depth Perception on Performance of Simulated Materials Handling Tasks

Abstract

A series of experiments were performed using ft laboratory simulation of a fork-lift truck setting task. In general, the same effects were observed as found in an another study using fork-lift trucks except that the direction of errors was reversed, showing a reversal of movement relationships in the simulator. The visual angle between the drivers' direction of motion and his line of sight to the target had a large effect on performance times and error rates. When this angle was less than 12°, both times and errors increased sharply. Performance times at different movement amplitudes and target widths were a linear function of an Index of Difficulty except for target widths of less than 2% of the amplitude. Subject age and experience of fork-lift truck driving had a significant effect of performance. Augmentation of vision using a closed circuit television display was beneficial to performance, reducing times by 14% and errors by 52% showing that this is an economic proposition for materials handling vehicles.     

Influence of carrying heavy loads on soldiers' posture,movements and gait

Military personnel are required to carry heavy loads whilst marching; this load carriage represents a substantial component of training and combat. Studies in the literature mainly concentrate on physiological effects, with few biomechanical studies of military load carriage systems (LCS). This study examines changes in gait and posture caused by increasing load carriage in military LCS. The four conditions used during this study were control (including rifle, boots and helmet carriage, totalling 8 kg), webbing (weighing 8 kg), backpack (24 kg) and a light antitank weapon (LAW; 10 kg), resulting in an incremental increase in load carried from 8, 16, 40 to 50 kg. A total of 20 male soldiers were evaluated in the sagittal plane using a 3-D motion analysis system. Measurements of ankle, knee, femur, trunk and craniovertebral angles and spatiotemporal parameters were made during self-paced walking. Results showed spatiotemporal changes were unrelated to angular changes, perhaps a consequence of military training. Knee and femur ranges of motion (control, 21.1° ± 3.0 and 33.9° ± 7.1 respectively) increased (p < 0.05) with load (LAW, 25.5° ± 2.3 and 37.8° ± 1.5 respectively). The trunk flexed significantly further forward, confirming results from previous studies. In addition, the craniovertebral angle decreased (p < 0.001) indicating a more forward position of the head with load. It is concluded that the head functions in concert with the trunk to counterbalance load. The higher muscular tensions necessary to sustain these changes have been associated with injury, muscle strain and joint problems.     

Neuromuscular and cardiovascular responses of Royal Marine recruits to load carriage in the field

Cardiovascular and neuromuscular responses of 12 male Royal Marine recruits (age 22 ± 3 years, body mass 80.7 ± 6.8 kg, VO(2)max 52.3 ± 2.7 ml kg(-1) min(-1)) were measured during 19.3 km of load carriage walking at 4.2 km h(-1) and carrying 31.0 kg. Heart rate during load carriage was 145 ± 10 beats·min(-1) (64 ± 5 %HRR) and showed a negative relationship with body mass (r = -0.72, P = 0.009) but no relationship with VO(2)max (ml kg(-1) min(-1); r = -0.40, P = 0.198). Load carriage caused a decrease in vertical jump height (8 ± 9%) and power (5 ± 5%) (P < 0.001). Change in vertical jump power showed a positive relationship with body mass (r(2) = 0.40, P = 0.029) but no relationship to VO(2)max (ml kg(-1) min(-1); r(2) = 0.13, P = 0.257). In conclusion, load carriage caused a reduction in vertical jump performance (i.e. decreased neuromuscular function). Lighter individuals were disadvantaged when carrying absolute loads, as they experienced higher cardiovascular strain and greater decreases in neuromuscular function.     

Effect of load position on physiological and perceptual responses during load carriage with an internal frame backpack

The purpose of this study was to determine the effect of load position in an internal frame backpack on physiological and perceptual variables. Ten female participants walked on a level treadmill for 10?min carrying 25% of their body weight in a high, central, or low position. The variables measured included oxygen consumption (VO₂), heart rate (HR), respiratory exchange ratio (R), respiratory rate (RR), minute ventilation (VE), and rating of perceived exertion (RPE). VO₂, VE, and RPE were significantly lower in the high position (18.6?±?2.3?ml/kg/min, 31.7?±?5.0?l/min, 2.8?±?0.8, respectively) compared to the low position (22.2?±?3.0?ml/kg/min, 38.6?±?7.5?l/min, 3.7?±?1.0, respectively). HR, R, and RR did not change significantly as the load was moved from the high (129.8?±?16.8, 0.89?±?0.06, 30.3?±?4.2, respectively) to the low position (136.0?±?25.3, 0.92?±?0.04, 33.8?±?5.2, respectively). The results of this study suggest that load placement is an important factor in the physiological and perceptual responses to load carriage, and that packing heavy items high in the backpack may be the most energy efficient method of carrying a load on the back.     

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.     

ABSTRACTING SERVICE

1. The methods which are commonly used in work physiology for rapid sampling, laboratory storage and analysis of expired air have been examined

2. The rapid fractional sampling of expired air from both a mixing chamber and a side arm sampling device produces significant differences in [Vdot]o_a values when compared to the standard Douglas method. However, provided the volume of the mixing chamber is above 4 litres, the differences are small for this technique, (293 ±18.1 mls) compared with the side arm technique (263.4± 62.9 mls), and introduce negligible error into the estimation of energy expenditure

3. The selective loss of CO₂ from butyl rubber bladders, Douglas bags and syringes was found to be 0.11 per cent/hr., 0.2 per cent/hr. and 0.007 per cent/hr. respectively during the 8 hr. period. Loss of CO₂ during the first 30 min was high in the case of the bladders and they were found to be very unsatisfactory storage containers. Douglas bags showed a negligible loss of CO₂ during the first 2 hours, but the concentration began to fall shortly thereafter. Syringes, on the other hand, showed no appreciable decline of CO₂ until after the 8th hour of storage Samples collected in glass tonometers by mercury siphoning and displacement of acidulated water still maintained their concentrations of O₂ and CO₂ after 56 days of storage

4. The Pauling (Beckman E₂ analyser was found to be an accurate, simple and fast method of estimating the O₂ concentration in expired air. The discrepancy between the methods was found to be of the order of ±0.15 vol per cent when compared with the conventional Haldane gas analysis method.     

The acceptable load while marching at a speed of 5km h-1 for young Chinese males

Ninety-three young Chinese men selected at random were involved in the load carrying experiments. They marched at 5 km h^?1 carrying loads of 0,15,20,25 and 31 kg for 7 h per day. At this speed the acceptable load to be carried was 20 kg. Under this load 95% of the men had heart rates below 120 btmin"’ while marching and energy metabolism was in balance. Nevertheless, 10-15% of the men were fatigued and felt tired.     

Postural adjustments while standing with two types of loaded backpack ∗

Two types of frame backpack, the internal-frame pack and the external-frame pack, are commonly used by hikers to carry heavy loads. The centre of volume of the internal-frame pack is lower and closer to the body than that of the external-frame type. This study examined how carrying each pack type changed the body posture compared with the typical standing posture as a control. The packs were loaded with 19?kg loads for the men and 14?kg loads for the women. The positions of the knees, hips, shoulders and ears were recorded photographically; the whole-body centre of gravity and the partial centres of gravity above the knee and hip were calculated. The nine female and seven male subjects were experienced in carrying packs. Both types of packs caused the subjects to lean forward; the bend was greatest above the hips but the knees and hips were also forward of the control position. The internal-frame pack caused a greater displacement and also a greater uncompensated torque at the hips: The female subjects overwhelmingly preferred the external-frame pack, while the male subjects preferred the internal-frame pack; no difference in parameters was seen between the men and the women that might explain these preferences. Although the internal-frame pack seems less adaptive in a static test, it would provide greater stability and less moment of inertia during walking.     

Effect of backpack fit on lung function

Carrying loads close to the trunk with a backpack causes a restrictive type of change in lung function in which Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1?s (FEV₁) are reduced without a corresponding decrement in the FEV₁.FVC^???1 %. It is not known whether this is due to the weight of the load acting on the chest or to the tightness of fit of the shoulder and chest straps and waist belt of the pack harness. This study examined FVC, FEV₁, FEV₁.FVC^???1 %, peak expiratory flow (PEF), forced expiratory flow between 0.2 and 1.2?s (FEF_0.2?–?1.2) after the start of expiration and between 25 and 75% of each FVC (FEF_25?–?75%) in 12 healthy males wearing a 15?kg backpack in which the shoulder and chest straps and hip belt were loosened by 3?cm from a ‘comfort fit’ to achieve a ‘loose pack’ fit (LPF) and tightened by 3?cm from CF to achieve a ‘tight pack’ fit (TPF). In comparison with the control condition of no pack, a loose pack fit significantly reduced FVC (by 3.6%, p?<?0.01), FEV₁ (by 4.3%, p?<?0.01) and FEF_25?–?75% (by 8.4%, p?<?0.01). A tight pack fit significantly reduced FVC (by 8.1%, p?<?0.01) and FEV₁ (by 9.1%, p?<?0.001). It also significantly reduced FEF_0.2?–?1.2 (by 7.3%, p?<?0.05) and FEF_25?–?75% (by 21%, p?<?0.01). In comparison with a loose pack fit, the tight pack fit was associated with a significantly lower FVC (by 4.6%, p?<?0.01), FEV₁ (by 5.0%, p?<?0.01), FEF_25?–?75% (by 13.8%, p?<?0.01) and a fall in FEF_0.2?–?1.2 (by 5.5%). The latter was approaching significance (p?=?0.077). There were no significant changes in FEV₁.FVC^???1% and PEF. It is concluded that tightening the fit of a backpack significantly affects lung function in a manner that is typical of a restrictive change in lung function and is very similar in pattern to that of wearing a loosely fitted loaded backpack. The effect of tightness of fit is additional to that due to the weight of the load alone and may also reduce expiratory flow at low lung volumes.     

Subjective perceptions of load carriage on the head and back in Xhosa women

The purpose of this study was to compare the subjective perceptual responses to both head-loading and back-loading in a group of Xhosa women. Thirty two women were divided into three groups based on their experience of head-loading and walked on a treadmill on two occasions, head-loading and back-loading, at a self selected walking speed for 4 min with a variety of loads until pain or discomfort caused the test to be terminated or a load of 70% body mass was successfully carried. After each workload there was a 1 min rest period during which the women indicated feelings of pain or discomfort in particular areas of the body via visual analogue scales. At the end of each test the women were asked to complete further questionnaires relating to pain and discomfort and on completion of the second test were also asked to compare the two loading conditions. Finally the women were interviewed to establish their history of load carriage and associated pain and discomfort. The data indicate that whilst back-loading was generally associated with more areas of discomfort than head-loading, the pain and discomfort in the neck associated with head-loading was the predominant factor in the termination of tests and that this was independent of head-loading experience. This early termination meant that, on average, the women could carry greater loads on their backs than on their heads. The study suggests that further work needs to be carried out to establish viable alternatives to head-loading for rural dwellers in Africa.     

Trunk muscle activity in different modes of carrying schoolbags

The daily load of carrying schoolbags is influenced by the mode of carriage. Electromyographic (EMG) activity from rectus abdominis and erector spinae was recorded bilaterally in five static conditions: no bag; shoulder bag; backpack; front pack; double pack. Nineteen students carried a load of 15% of their body weight. A double pack, with the load equally distributed in a front and a backpack, showed no significant differences in EMG activity compared with unloaded standing. The activity levels of erector spinae significantly decreased while carrying a backpack and increased with a shoulder bag and a front pack. Rectus abdominis revealed significantly higher EMG levels in the backpack trial. Asymmetrical activity between the right and the left part of the back muscles was clearly observed while carrying a shoulder bag with the weight at the right side of the body. The abdominal muscles revealed a slightly significant asymmetry for the shoulder bag and, surprisingly, also for the backpack. These findings suggest that the physical stresses associated with carrying book bags can be minimized by the design of a double pack. Asymmetry in muscle activity may indicate a failure of trunk stabilization and contribute to the development back pain.     

Load carriage for fun: a survey of New Zealand trampers, their activities and injuries

Much of the published research investigating the physiological, biomechanical and psychological impact of load carriage by backpack has studied young, fit males carrying loads for an hour or less. The resultant body of knowledge may not be appropriate to the increasing numbers of middle-aged and older men and women who are taking up or returning to tramping as a recreational activity. In this study, members of 11 tramping clubs throughout New Zealand were surveyed to discover their personal characteristics, characteristics of tramping trips undertaken and injuries sustained. Significant numbers of men and women over 30, 40 and 50 years of age and with generally sedentary lifestyles reported occasional tramping during which they carried backpacks weighing up to 29% of their body weight for more than five hours over 11–15 km/day. Injuries were reported by 74%, with sprains being the most common injury type and knees, ankles and feet the most frequent location of injury. These findings may have implications for route planning and the design of interventions to reduce injuries, health care, training, tracks, equipment and footwear, and demonstrate the need for further research to investigate the risks and requirements of recreational trampers.