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.     

Biomechanical and metabolic effects of varying backpack loading on simulated marching

Twelve healthy, male Army recruits performed three, 40-min treadmill marches at 6 km/h, under three load carriage conditions: 0%-body weight (BW) backpack load, 15%-BW load and 30%-BW load. Kinematic and kinetic data were obtained, immediately before and after each treadmill march, for computing ankle, knee and hip joint rotations and moments. Metabolic data (oxygen uptake (VO2), expired ventilation (VE), respiratory exchange ratio (RER)), heart rate (HR) and ratings of perceived exertion (RPE) were collected continuously during marching. Significant differences (p < or = 0.05) were observed between each load for VO2, HR and VE throughout the marches. At 40 min, relative energy costs for 0%-BW, 15%-BW and 30%-BW loads were 30, 36 and 41% VO2max, respectively. RPE responses during marching significantly differed for only the 30%-BW load and were greater than responses at 0%-BW and 15%-BW loads. During load carriage trials prior to treadmill marches (pre-march), peaks in internal, hip extension, knee extension and ankle plantar flexion moments increased with increasing backpack load. Relative to 0%-BW load, percentage increases in knee moments, due to 15%-BW and 30%-BW loads, pre-march, were substantially larger than the percentage increases for hip extension and plantar flexion moments, pre-march. Pre-march and post-march peaks in hip extension and ankle plantar flexion moments were similar with all loads, while notable pre-march to post-march declines were observed for knee extension moment peaks, at 15%-BW and 30%-BW load. Pre-march joint loading data suggests that the knee may be effecting substantial compensations during backpack loaded marching, perhaps to attenuate shock or reduce load elsewhere. Post-march kinetic data (particularly at 15%-BW and 30%-BW load), however, indicates that such knee mechanics were not sustained and suggests that excessive knee extensor fatigue may occur prior to march end, even though overall metabolic responses, at 15%-BW and 30%-BW load, remained within generally recommended limits to prevent fatigue during prolonged work.     

Maximal physiological responses to deep and shallow water running

The maximal physiological responses to treadmill running (TMR), shallow water running (SWR) and deep water running (DWR) while wearing a buoyancy vest were compared in 15 trained male runners. Measurements included oxygen consumption (VO2 max), respiratory exchange ratio (RER) and heart rate (HR). Treadmill running elicited VO2 max and HRmax, which were higher than the peaks attained in both water tests (p < 0.01). VO2 peak averaged 83.7 and 75.3% of VO2 max for SWR and DWR respectively. Peak HR for SWR and DWR were 94.1 and 87.2% of the HRmax reached in the TMR. RER responses were similar between the three modalities. The observations suggest that the training stimulus provided by water is still adequate for supplementary training. While SWR is potentially an efficient method of maintaining cardiovascular fitness, it needs to be investigated further to establish if it is a viable technique for the injured athlete to employ.     

Comparison of five modes of carrying a load close to the trunk†

Abstract

This study was designed to investigate the cardiorespiratory, metabolic, and subjective responses to carrying a load close to the trunk in five different ways. Each of five subjects carried a load equivalent to 35% body weight (BW) for one hour at 4-5 km hr^?1 and 0%grade on a motor driven treadmill using each of the following modes of load carriage: (1) the total load carried in a backpack with frame (BP/F), (2) the total load carried in a backpack with no frame (BP/NF), (3) half the load in a backpack (with frame) and half in pouches attached to a waist belt (BP/WB), (4) half the load in a backpack (with frame) and half in a front pack on the chest (BP/FP), and (5) the total load carried as a trunk jacket (TJ), i.e. a military type ‘flak’ jacket with weights inserted in pockets evenly distributed about the trunk. There were no statistically significant differences in the mean cardiorespiratory and metabolic costs associated with each of the five modes of load carriage. However, BP/FP and TJ were subjectively rated as significantly (P < 001) more comfortable than BP/F and BP/NF, suggesting that there may be physiological differences between the five modes of load carriage which were not detected by the cardiorespiratory and metabolic measurements used in this study (i.e. heart rate, oxygen consumption and minute ventilation). In contrast, the BP/FP was reported to be the hardest to don and doff and was associated with a statistically significant (P <0-05) restrictive type of ventilatory impairment. In conclusion, in practical terms there may seldom be a single ‘best’ way to carry a 35% BW load close to the trunk.     

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.     

Changes in neck muscle electromyography and forward head posture of children when carrying schoolbags

This study tested the effects of three alternative types of backpack on head posture and neck muscle electromyography (EMG) in children. Four loading conditions were tested: no pack; a backpack; a double pack; a modified double pack (designed with a backpack and a front pack weighing 10% and 5% of body weight, respectively). Dependent variables were neck muscle activity, forward head angle and forward head distance (the perpendicular distance from C7 to a vertical line through the tragus of the ear). Fifteen children were asked to walk at a speed of 0.8 m/s on a treadmill. The EMG activity of upper trapezius, sternocleidomastoid and midcervical paraspinals muscles and the forward head angle and forward head distance were all significantly higher when carrying a backpack than for the other conditions. When carrying a double pack, there was a backward head posture characterised by an increased negative forward head angle, decreased forward head distance, increased sternocleidomastoid EMG signal and decreased midcervical paraspinals EMG signal, compared to carrying no pack. When carrying a modified double pack, the forward head angle and forward head distance decreased when compared to carrying a backpack. These findings indicate that the modified double pack minimises postural deviation.     

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.     

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.     

Biomechanical and metabolic effects of varying backpack loading on simulated marching

Twelve healthy, male Army recruits performed three, 40-min treadmill marches at 6 km/h, under three load carriage conditions: 0%-body weight (BW) backpack load, 15%-BW load and 30%-BW load. Kinematic and kinetic data were obtained, immediately before and after each treadmill march, for computing ankle, knee and hip joint rotations and moments. Metabolic data (oxygen uptake ([Vdot]O₂), expired ventilation ([Vdot]E), respiratory exchange ratio (RER)), heart rate (HR) and ratings of perceived exertion (RPE) were collected continuously during marching. Significant differences (p?0.05) were observed between each load for [Vdot]O₂, HR and [Vdot]E throughout the marches. At 40 min, relative energy costs for 0%-BW, 15%-BW and 30%-BW loads were 30, 36 and 41% [Vdot]O₂max, respectively. RPE responses during marching significantly differed for only the 30%-BW load and were greater than responses at 0%-BW and 15%-BW loads. During load carriage trials prior to treadmill marches (pre-march), peaks in internal, hip extension, knee extension and ankle plantar flexion moments increased with increasing backpack load. Relative to 0%-BW load, percentage increases in knee moments, due to 15%-BW and 30%-BW loads, pre-march, were substantially larger than the percentage increases for hip extension and plantar flexion moments, pre-march. Pre-march and post-march peaks in hip extension and ankle plantar flexion moments were similar with all loads, while notable premarch to post-march declines were observed for knee extension moment peaks, at 15%-BW and 30%-BW load. Pre-march joint loading data suggests that the knee may be effecting substantial compensations during backpack loaded marching, perhaps to attenuate shock or reduce load elsewhere. Post-march kinetic data (particularly at 15%-BW and 30%-BW load), however, indicates that such knee mechanics were not sustained and suggests that excessive knee extensor fatigue may occur prior to march end, even though overall metabolic responses, at 15%BW and 30%-BW load, remained within generally recommended limits to prevent fatigue during prolonged work.     

The influence of speed, grade and mass during simulated off road bicycling

The purpose of this investigation was to examine the effects of bicycle mass, speed, and grade on oxygen consumption (VO2), heart rate (HR), and ratings of perceived exertion (RPE) during a simulated off-road riding paradigm. Nine adult subjects with mean +/- SD age, mass, and VO2 max of 26.1 +/- 5.6 years, 71.7 +/- 7.5 kg, 56.6 +/- 5.2 ml x kg(-1) x min(-1) respectively, were trained to ride a fully suspended Trek Y-22 mountain bike on a treadmill with a 3.8 cm bump affixed to the belt. Riders completed a maximum of nine separate trials encompassing three different bike masses (11.6, 12.6 and 13.6 kg), 3 speeds (2.7, 3.6 and 4.5 m x s(-1)), and 3 grades (0, 2.5, and 5%). Throughout a trial, bike mass and speed remained constant while riding grade was increased every 5 min. During simulated off-road riding on a fully suspended mountain bike, increases in speed and grade significantly increased VO2, heart rate, and RPE. Increases in bike mass had no significant effects on VO2, heart rate or RPE. In addition, speed and grade changes interacted to differentially affect VO2, heart rate, and RPE at all speeds and grades.     

Decreased submaximal oxygen uptake during short duration oral contraceptive use: a randomized cross-over trial in premenopausal women

Long-term oral contraceptive (OC) use is known to be associated with changes in haemostasis, cardiovascular dynamics, and carbohydrate and lipid metabolism. Less well documented are the short-term variations in cardiorespiratory responses to exercise during the menstrual cycle of OC users. In this study the short-term effects of the usage of OC on cardiorespiratory and ventilatory responses to submaximal exercise were examined. Ten women (age = 23 +/- 3 years) on monophasic OC were tested at three different times during their 'cycle': during menstruation, off OC use (off OC: days 2-4), early on OC use (EOC: days 7 - 9) and late on OC use (LOC: days 19 - 21). Times of testing were assigned randomly. On each occasion participants performed a continuous 12-min run exercise on a treadmill at three submaximal intensities (averaging 7, 8 and 9 km h(-1)), each for 4 min. Heart rate, ventilation (VE), oxygen uptake (VO2), carbon dioxide output (VCO2), respiratory exchange ratio and running economy were assessed in the last minute of each stage of exercise. No significant variations were observed between the different times for heart rate, VE, and VCO2 irrespective of the stage of exercise (p > 0.05). Using two-way analysis of variance (ANOVA) with repeated measures on both factors (three stages and three times), VO2 (ml kg(-1) min(-1)) was lower by 3% to 5.8% when participants were on early and late OC use compared to off OC regardless of the stage of the exercise (F(2,18) = 6.3; p = 0.008). Running economy (ml O2 kg(-1) km(-1)) was significantly improved (lower values) when women were on late OC use compared to off OC regardless of the stage of exercise. No significant interaction effect between stage of exercise and time of pill usage was demonstrated in any of the parameters studied. Results suggest that oral contraceptive users may expect lower VO2 and better running economy during the pill ingestion phase and consequently have implications for exercise performances.     

Ergonomics diary

Physiological, perceptual and physical responses to a typical circuit weight-training (CWT) regimen were recorded in two studies. The aims were to assess the intensity of exercise during CWT; and to determine whether physical responses as evaluated by spinal shrinkage were related to physiological and perceptual responses to CWT. In the first study (n = 10) heart rate (HR), oxygen consumption (VO), ventilation (VE), blood lactate (La) and perceived exertion (RPE) were measured in response to CWT. Mean ( ± SD) time to complete three circuits of CWT was 17.8 (± 1-4) min. The HR max, VO₂max and peak La, measured first during an incremental treadmill test, were 195 (±13) beats.min ^?159-7 (±4-8) ml.kg^?1.min^?1 and 14-3 (±3-5) mM respectively. Mean HR and vO₂ during CWT were 69% and 50% of the respective maximal values. The HR-VO₂ ratio observed on the treadmill was elevated during CWT, with VO₂ being lowered relative to HR. Mean VE and La values were 52-7 (± 14-5) l.min^?1 and 6-9 ( ± 3-6) mM. The effect of the same CWT regimen on spinal loading as indicated by change in stature (shrinkage) was investigated in a second study (n = 8). The mean ( ± SD) time taken to complete the circuit was 17-4 ( ± 1-3) min. Mean shrinkage due to CWT (2-5 ± 1 -5?mm) was unrelated to the time taken to complete the circuits, to HR, RPE or to low back pain ratings (p > 0-05). Observations suggest that CWT as represented in these studies engages anaerobic as well as aerobic mechanisms but the exercise intensity may not provide sufficient stimulation for aerobic training. The physical load on the spine indicated by spinal shrinkage was not related to the physiological or perceptual strain.     

Physiological strain during kitchen work in relation to maximal and task-specific peak values

Six female and three male subjects from a hospital kitchen volunteered for the study. The subjects were working on a conveyor belt collecting and sorting dirty plates, glasses and cutlery for cleaning. In the study, a medical examination, a maximal clinical exercise test with a 12-lead electrocardiogram (ECG) and a maximal arm cranking test were performed in the laboratory. Further, each subject was studied for 30 min during a normal work shift in the kitchen. Oxygen uptake (VO2) and heart rate (HR) were continuously registered. During the work period, a rating of perceived exertion (RPE) was asked at the 5th, 15th and 30th minute. Physiological responses were measured by a portable system (K4) both in the laboratory and in the field. VO2 and HR measured in the field were proportioned to corresponding maximal values during cycling and to peak values during arm-cranking. The mean VO2 for the male and the female subjects during kitchen work was 0.65 +/- 0.16 l min-1. This corresponded to 24% of VO2max and to 41% of VO2peak during arm-cranking. The difference was significant (p < 0.001). Owing to a magnetic field at the conveyor belt, reliable HR values were obtained only from the female subjects. The mean HR during work among the female subjects was 101 beats min-1. It corresponded to 55% of HRmax and 67% of HRpeak during arm-cranking (p < 0.05). The present study shows that the relative work intensity is markedly higher when it is expressed relative to the corresponding muscle group's VO2peak instead of the VO2max. Similar difference was also seen in the HR response. More task-specific testing of physical capacity may provide improved evaluation of physical strain in a job.     

Oxygen consumption during fire suppression: error of heart rate estimation.

Ten male firefighters were tested on a treadmill to determine their heart rate (HR) x oxygen consumption (VO2) relationship. These men then performed a simulated fire suppression protocol during which HR and VO2 were measured simultaneously by a portable physiological monitoring system. Average VO2 in the simulated setting was 31.0 +/- 7.0 ml.kg-1.min-1 at a HR of 176 +/- 9 bpm. This VO2 was significantly (p less than or equal to 0.05) less than the VO2 that would have been predicted by treadmill testing (38.9 +/- 5.0 ml.kg-1.min-1) at a corresponding HR. Fifty-nine per cent of this variability could be accounted for by regression analysis. Firefighters worked on average at 73 +/- 10% VO2 max with a range of 54% to 88%. There was a significant (-0.82; p less than or equal to 0.05) inverse relationship between performance time of the fire suppression protocol and the relative intensity of VO2 max at which the firefighters worked. These findings indicate that the prediction of energy expenditure from HR is not straightforward in fire suppression settings. Furthermore, the relative intensity of work firefighters self-select is variable and should be considered as an additional physiological determinant of work behaviour.     

Cardiorespiratory and thermoregulatory response of working in fire-fighter protective clothing in a temperate environment

The cardiorespiratory and thermal responses of two intensities of treadmill exercise were compared for brief periods (12 min) in fire ensemble (FE) but without self contained breathing apparatus, and sports ensemble (SE), in a temperature environment. A further experiment explored the responses of subjects exercising in FE over a prolonged period (60 min). Eighteen male fire-fighters wearing either FE or SE walked on a level treadmill for 6 min at 5 km x h(-1) increasing to 7 km x h(-1) for 6 min. Following a recovery interval of 1 h, the exercise protocol was repeated in the second ensemble; the order of ensemble was balanced. Heart rate (HR), rectal temperature (Tre), VO2 max and rating of perceived exertion (RPE) were monitored continuously under both ensembles. At 7 km x h(-1), VO2 was significantly higher (p<0.05) in FE (36.1 and 39.9 ml x kg(-1) x min(-1)) than in SE and represented 74% VO2 max. There were no changes Tre. In experiment 2, following a rest interval of at least 36 h, eight subjects in FE walked on the treadmill at 6 km x h (gradient 10%) for 60 min also in temperate conditions, where HR, Tre and RPE were recorded at 10-min intervals. During the 60-min exercise in FE, HR reached 161 beats x min(-1) and Tre increased to 38.3 degrees C. Despite considerable subject discomfort, Tre remained below dangerous levels (38.4 degrees C). When RPE were compared with a physiological strain index (PSI) calculated from Tre and HR data over 60 min, there was no significant difference (p<0.05) with a correlation coefficient (r) of 0.98. The results suggest that RPE and PSI are closely related when exercise is sufficiently prolonged or intense to elevate Tre and HR in fire-fighters wearing FE in temperate conditions. If further investigation confirms this relationship for hot humid conditions in which fire-fighters operate, then with training, it may provide individuals with a valid measure of dangerous levels of perceived heat strain.     

Comparison of work rates, energy expenditure, and perceived exertion during a 1-h vacuuming task with a backpack vacuum cleaner and an upright vacuum cleaner

The purpose of this study was to evaluate two types of industrial vacuum cleaners, in terms of cleaning rates, energy expenditure, and perceived exertion. Twelve industrial cleaners (six males and six females, age 28-39 yr) performed two 1-h vacuuming tasks with an upright vacuum cleaner (UVC) and a backpack vacuum cleaner (BPVC). Measures for oxygen uptake (VO2) and ratings of perceived exertion (RPE) were collected continuously during the 1-h vacuuming tasks. Cleaning rates for the UVC and BPVC were 7.23 and 14.98 m2min(-1), respectively. On a separate day subjects performed a maximal treadmill exercise test to determine their maximal aerobic capacity (peak VO2). Average absolute energy costs (in Metabolic equivalents), relative energy costs of the vacuum task compared to the subjects' maximal aerobic capacity (% peak VO2), and RPE responses for the 1-h vacuuming tasks were similar between vacuum cleaners, but % peak VO2 and RPE values differed between genders. These results indicate that the BPVC was more efficient than the UVC. With the BPVC, experienced workers vacuumed at a cleaning rate 2.07 times greater than the UVC and had similar levels of energy expenditure and perceived effort, compared to the slower cleaning rate with the UVC.     

School backpack design: A systematic review and a summary of design items

The purpose of this paper is to systematically review the recent literatures to obtain a summary of significant items (see Table B1) for better student backpack design for health improvement, as well as to identify gaps for further research. A systematic review was performed in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), targeting papers of the last 20 years. Thirty-six studies were included, assessed and synthesised. Four categories of design-related items were summarised: Biomechanical consideration, Strap, Dimension and Carrying method. Quality assessments were completed for the included studies by utilising different tools. The major health outcomes associated with the design-related items were posture, perception, metabolic cost, lung function, contact pressure of foot or shoulder, and muscle activity. An optimal location for the centre of mass of a backpack could not be ascertained from this review in the aspect of spinal curvature and postural displacement, and there was usually no best input that induced the best outcome in every dimension. Oscillation in the medial-lateral direction should be minimised, and wider shoulder strap should be utilised, together with hip straps. Different carrying methods, such as double pack, BackTpack, modified backpack, and frontpack, were superior to the traditional backpack, whereas the single-strap pack should be avoided. Some gaps, such as lack of standardised protocol and evidence for clinical significance, were identified. Meanwhile, the risk of bias is commonly high for recent studies.     

Effect of single and double strap backpacks on lung function

Carrying heavy and moderate military loads in backpacks or as body armour compresses the chest, causing a change in lung function that is typical of a restrictive ventilatory impairment. It is not known if a lighter backpack load of only 6 kg, such as is typical of loads carried by students, will have a similar effect on lung function. There have been no studies examining whether backpacks of different strapping styles have an effect on lung function. Several designs of student backpack have recently been introduced to the market. One of the most popular is a single-strap backpack. This study examined Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), FEV1.FVC( - 1)% and Peak Expiratory Flow (PEF) in 13 participants (4 males, 9 females) wearing each of two 6 kg backpacks, one with two shoulder straps (a Double Strap Backpack (DSB)) and the other with a single strap (a Single Strap Backpack (SSB)) worn across the shoulder and chest. In comparison with the control of no pack (N), SSB significantly reduced FVC (by 3.94%, p = 0.006) but there were no significant differences in FEV1, FEV1. FVC( - 1)% and PEF. The DSB also significantly reduced FVC (by 1.97%, p = 0.034) but no significant differences were found in FEV1, FEV1. FVC( - 1)% and PEF measures. In comparison with DSB, the SSB was associated with a significantly lower FVC (by 2.05%, p = 0.049) and FEV1 (by 1.88%, p = 0.029) but there were no significant changes in FEV1. FVC( - 1)% and PEF. It is concluded that a backpack load of 6 kg could produce a mild restrictive type of ventilatory impairment in lung function. This effect was greater for a single cross-chest strap than for a more conventional double strap harness.     

一种保护青少年脊柱健康的减重背包设计与研究

目前市面上的青少年背包主要通过肩部来进行载荷,而忽略了腰部载荷的作用。背包长期负重 不当会影响脊柱生长。为了平衡肩部、腰部和臀部的载荷,设计一种通过臀部带和弹性杆结构改变重力传递方 式的减重背包。首先对人体背包进行生物力学分析,提出设计方案;然后借助 ADAMS 对传统背包与减重背包 在平地、上坡、下坡 3 种路况下进行人体肩部、腰部和臀部载荷的动力学仿真,并利用 MATLAB 对 2 种背包 的肩部、腰部和臀部的力矩进行分析。结果表明减重背包减轻了肩部 6.1%和腰部 5.4%力矩;减重背包肩部力 矩与腰臀部合力矩的比值是 4.17,而传统背包的比值是 6.58。减重背包减少了肩部和腰部的载荷,同时发现肩 部力矩与腰、臀部合力矩的比值越小,转移到臀部的力矩越大,背包的平衡性越好,表明了减重背包优于传统 背包。     

Bicycle messengers: energy expenditure and exposure to air pollution

The purpose of the study was to determine the level of energy expenditure and exposure to air pollution for bicycle messengers. Relationships between heart rate (HR) and oxygen uptake, and between HR and pulmonary ventilation (VE) for each participant were established in laboratory tests. Air pollution and HR were measured during one working day. The total oxygen uptake was then described as the total energy expenditure in Joule (J) and in multiples of the energy expenditure at rest (MET). The mean energy expenditure during a working day (8 h) was 12 MJ, (4.8 MET). The level of air pollution exposure when cycling seemed to be comparable with the levels of exposure when sitting inside a vehicle. The VE during cycling was four times higher than resting value. Increased VE led to increased exposure to air pollution.