Physiological factors of importance for load carriage (original) (raw)
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Differentiated perceptions of exertion and energy cost of young women while carrying loads
European Journal of Applied Physiology and Occupational Physiology, 1982
Differentiated local ratings of perceived exertion from the legs and central ratings from the chest, and oxygen consumption, were determined during load carriage in seven young women. Subjects walked for 6 rain at 3.22, 4.83, 6.44, or 8.05 km-h -1 carrying (1) no load, (2) a load equal to 7.5% of body weight (mean: 4.66 kg) or (3) a load equal to 15% of body weight (mean: 9.32 kg). Thus, each subject underwent 12 separate tests. The external loads were in the form of lead pellets carried in a plastic scuba belt worn around the waist. A differentiation threshold was found at 6.44 km 9 h -1 for the 0% and 7.5% loads and at 4.83 km 9 h -1 for the 15% load. At speeds below the threshold, the perception of exertion was similar in the legs, chest and overall. At higher speeds, exertion was perceived to be more intense in the legs than overall and less intense in the chest than overall, suggesting that the local legs signal was the dominant factor in shaping the overall sensation of exertion. The oxygen uptake was greater for the 15% load than for either the 0% or 7.5% loads, but was similar for the 0% and 7.5% loads. Findings suggested a critical weight limit for external loads that could be transported without increasing the metabolic cost beyond that required to move the body weight alone. This limit fell between 7.5% and 15% of the body weight. When oxygen uptake was expressed per kg of total weight transported, there was no loss of metabolic efficiency while carrying loads up to 15% of the body weight.
Occupational medicine (Oxford, England), 2005
To test the hypothesis that measures of aerobic fitness, body mass and indices of body composition will influence the metabolic and cardiovascular demands of simulated load-carriage tasks. Twenty-eight healthy male volunteers, following assessment of maximal oxygen uptake (O(2)max) and body composition, walked on a treadmill at 4 kph (1.11 m/s) for 60 min on gradients of 0, 3, 6 and 9% whilst carrying backpack loads of 0, 20 and 40 kg. During the final 3 min of each 5-min exercise bout, indirect respiratory calorimetry and heart rate data were collected and the 'steady-state' metabolic O(2) and cardiovascular (heart rate) demands quantified. Absolute O(2)max (ml/min) produced the strongest correlation (r = -0.64, P < 0.01) with the metabolic demand of heavy load-carriage (40 kg). The body composition index lean body mass/(fat mass + external load) produced a moderate correlation (r = -0.52, P < 0.01) with the metabolic demand of heavy load-carriage. The increases in me...
Effect of load and speed on the energetic cost of human walking
European Journal of Applied Physiology, 2005
It is well established that the energy cost per unit distance traveled is minimal at an intermediate walking speed in humans, defining an energetically optimal walking speed. However, little is known about the optimal walking speed while carrying a load. In this work, we studied the effect of speed and load on the energy expenditure of walking. The O2 consumption and CO2 production were measured in ten subjects while standing or walking at different speeds from 0.5 to 1.7 m s−1 with loads from 0 to 75% of their body mass (M b). The loads were carried in typical trekker’s backpacks with hip support. Our results show that the mass-specific gross metabolic power increases curvilinearly with speed and is directly proportional to the load at any speed. For all loading conditions, the gross metabolic energy cost (J kg−1 m−1) presents a U-shaped curve with a minimum at around 1.3 m s−1. At that optimal speed, a load up to 1/4 M b seems appropriate for long-distance walks. In addition, the optimal speed for net cost minimization is around 1.06 m s−1 and is independent of load.
The Physiology and Biomechanics of Load Carriage Performance
Military Medicine, 2018
Introduction: The weight that soldiers are required to carry in training and in combat has continually increased over the years. Changes in load carried or pace of activity will alter the physiological and biomechanical stress associated with the activity. Whether it is part of the soldier's training or an actual operation, managing the proper load and speed to minimize fatigue can be integral to the soldier's success. Without a proper understanding of the multitude of factors that may affect load carriage performance, mission success may be jeopardized. The purpose of this review is to summarize and clarify the findings of load carriage research and to propose a new method for analyzing the intensity of load carriage tasks, the Load-Speed Index. Materials and Methods: We reviewed studies that examined military load carriage at walking speeds and included articles that featured non-military participants as deemed necessary. Results: Major factors that can affect load carriage performance, such as speed of movement, load carried, load placement, body armor, and environmental extremes all influence the soldier's energy expenditure. A critical aspect of load carriage performance is determining the appropriate combination of speed and load that will maximize efficiency of the activity. At the higher end of walking speeds, the walk-to-run transition represents a potential problem of efficiency, as it may vary on an individual or population basis. Conclusions: This review provides a comprehensive overview of these factors and suggests a new Load-Speed Index, which can be utilized to define thresholds for load and speed combinations and contribute to the understanding of the physiological and biomechanical demands of load carriage marches. The literature recommends that load and speed should be managed in order to maintain an exercise intensity~45% VO 2 max to delay time to fatigue during prolonged marches, and the Load-Speed Index corroborated this finding, identifying 47% VO 2 max as a threshold above which intensity increases at a greater rate with increases in load and speed. The Load-Speed Index requires validation as a predictive tool. There are no definitive findings as to how load affects the speed at which the walk-to-run transition occurs, as no investigations have specifically examined this interaction. Additional research is clearly needed by examining a wide range of loads that will facilitate a clearer understanding of speed and load combinations that optimize marching pace and reduce energy expenditure.
Journal of Human Kinetics, 2013
Walking is considered a fundamental method of movement and using a backpack is a common and economical manner of carrying load weight. Nevertheless, the shock wave produced by the impact forces when carrying a backpack can have detrimental effects on health status. Therefore, the aim of this study was to investigate differences in the accelerations placed on males and females whilst carrying different loads when walking. Twenty nine sports science students (16 males and 13 females) participated in the study under 3 different conditions: no weight, 10% and 20% body weight (BW) added in a backpack. Accelerometers were attached to the right shank and the centre of the forehead. Results showed that males have lower accelerations than females both in the head (2.62 ± 0.43G compared to 2.83 + 0.47G) and shank (1.37 ± 0.14G compared to 1.52 ± 0.15G; p<0.01). Accelerations for males and females were consistent throughout each backpack condition (p>0.05). The body acts as a natural shock absorber, reducing the amount of force that transmits through the body between the foot (impact point) and head. Anthropometric and body mass distribution differences between males and females may result in women receiving greater impact acceleration compared to men when the same load is carried.
Cardio-Respiratory and Metabolic Changes during Continuous Uphill-Downhill Load Carriage Task
Department of Human Physiology with Community Health , Vidyasagar University , Midnapore , West Bengal, 2015
Indian Army soldiers are deployed in hilly and mountainous regions of eastern and western part of the Himalayas to guard the borders. In this context they are required to march uphill and downhill with moderate to heavy load continuously for long duration. The physiological cost of such activities has been of specific interest for maintenance of optimum soldier performance. Studies on physiological changes during continuous uphill and downhill climbing are rare. A study was therefore undertaken to find the effect of uphill and downhill walk with load on the physiological parameters in laboratory conditions. Twelve soldiers with mean (± SD) age-26.8 (± 3.9) yrs, height-170.6 (± 3.2) cm and weight 66.2 (± 6.8) kg participated in the study as volunteers to measure the energy cost and physiological changes of continuous uphill and downhill load carriage task. The soldiers were subjected to treadmill walking at a speed of 3 km/ h. They had to undergo continuous uphill walking at 0, 5, 10, 15 and 20% gradients and downhill walking in the opposite manner. Participants walked 6 mins in each gradient. Total duration of walk was 60 min. The volunteers carried 10.7 and 21.4 kg load beside without load. Oxygen consumption (VO 2), Heart rate (HR), and energy expenditure (EE), were measured breath by breath using Metamax 3B system throughout the test. Relative work load (RWL, %VO 2 max) was calculated as percentage of VO 2 max. Repeated measure ANOVAs were used to predict level of significance across the experimental conditions. The mean (± SD) VO 2 max of the participants was found to be 52.6 (± 3.8) ml/min/kg. All the physiological parameters increased significantly with the increase in uphill gradient irrespective of the loads. VO 2 , EE and %VO 2 max decreased till 5% downhill gradient, but slight increase was observed at the level walking. HR continued to decrease till the downhill walking reached 0% gradient with and without load. Relative work load reached above the recommended limit (35% of VO 2 max) at 10% and above uphill gradients in both the load conditions. This information will be helpful in making strategy for designing uphill and downhill load march in mountains for Army personnel and hitch hikers.
The effects of mass (0, 5.4, 10.4 kg) and the type of support (on the shoulder or on waist) on physiological and mechanical strain indices of four young male subjects were quantified. While standing, oxygen uptake was not influenced by the type or mass of the backpack, and averaged 10% maximal oxygen uptake. The heart rate increased significantly by 9 beats per min while standing wearing a backpack. While walking (1.33 m . s -1 ) the mass significantly influenced both the heart rate and the oxygen uptake carried, but both types of strain remained below the tolerance limits for prolonged wear. Standing supporting a load did not significantly increase the EMG signal of the trapezius shoulder muscle (pars descenders). While walking, load carrying significantly increased the EMG of the shoulder muscles. The pressure on the skin under the shoulder straps during load carrying on the shoulders was more than a factor of three times higher than the threshold value for skin and tissue irritation. Load transfer to the waist with a flexible frame reduced the pressures on the skin of the shoulder to far below the threshold value. On basis of these results it was concluded that even with relatively low loads the limiting factor was the pressure on the skin, if a waist belt did not relieve such pressure on the shoulders.