Load stress; carrier strain: implications for military and receational backpacking

This paper reviews a growing literature on the stress of backpacking, particularly in military situations. Conceptual issues are raised and the implications for recreational backpackers are addressed. Under moderate to fairly heavy loading the energy cost, per kg total load carried, per hour, relates almost linearly to walking speed. Empirical data from studies in this unit are presented as benchmark indicators for use by recreational backpackers

The Relationship between Fitness and Marksmanship in Police Officers

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EFFECTS OF LOAD CARRIAGE ON SHOULDER NEUROMUSCULAR FUNCTIONS AND RECOVERY

Load carriage is a primary source for injury occurrence among military personnel and recreational hikers affecting all body areas. The shoulder ranks as the second or third most common site of injuries among military personnel. Many studies report that elevations in self-reported fatigue, soreness, and discomfort in the shoulders accompany the load carriage. Almost 50% of military personnel experienced a load carriage injury during the first episode of training, and 75% of those injured suffered a second injury during their career. The goal of this research project is to investigate the components associated with load carriage shoulder symptoms to determine which factor is a more substantial contributor to the cause of shoulder pain and injury. The first purpose of this dissertation was to investigate the effect of load carriage on shoulder strength and endurance, nerve amplitude and latency, and shooting accuracy. Experimental comparison between the neuromuscular functions before and after the load carriage of 20.5 kg was investigated in the first and second study. The second purpose was to determine the recovery time needed for the neuromuscular measures that were affected with load carriage task. The first study demonstrated that load carriage caused a significant decrement in shoulder strength, shoulder endurance, and nerve amplitude. The second study demonstrated that the load carriage task resulted in decreased strength, yet recovered in thirty minutes. Similarly, a decrement in nerve amplitude resulted but recovered in five minutes. The results of these studies suggest that load carriage mainly causes physical fatigue which affects shoulder strength. Fatigue could compromise the ability to perform overhead physical tasks if sufficient recovery time is not permitted

EFFECT OF LOAD CARRIAGE ON TACTICAL PERFORMANCE

Special Weapons and Tactics (SWAT) operators are specially trained personnel that are required to carry equipment to perform high risk tasks. Given the need to carry this equipment, it is important to understand the potentially deleterious effect that the additional load may have on tactical performance. Furthermore, it is important to identify physical fitness characteristics that are associated with the potential decrement in performance. Therefore, the purpose of this study was to evaluate the effect of load carriage on tactical performance and identify fitness characteristics associated with any decrement in performance. Twelve male operators performed a simulated tactical test (STT) on a live firing range with (loaded condition) and without external equipment (unloaded condition) and completed a battery of physical fitness assessments. Time to complete the STT in the loaded condition increased by 7.8% compared to the unloaded condition. Nine of the 13 STT tasks were performed significantly slower in the loaded condition. VO2peak was negatively associated and fatigue index was positively associated with the overall STT delta time. These findings indicate that a higher aerobic capacity and lower anaerobic fatigability are related to a greater resilience to carrying a load while performing tactical tasks

EFFECTS OF HEAT STRESS AND EXERCISE ON SHOOTING PERFORMANCE

Purpose: The purpose of this study was to evaluate the effects of exercise and acute heat stress on marksmanship performance measures of accuracy, precision, aim time, and distance travelled by the point of aim in trained US military veterans. Methods: Subjects (N=8) (height 184.1 ± 10.9 cm (SD), weight 92.1 ± 10.6 kg, 21.1 ± 8.9% body fat, VO2max 47.25 ± 7.36 mL/kg/min, age 26.8 ± 4.3 yrs.) completed one-hour of walking at 50% VO2max in a hot (35˚C, 30% maximal relative humidity) or cool (22˚C, 30% maximal relative humidity) environment. Core temperature, heart rate (HR), and physiological strain index (PSI) were recorded throughout the exercise period. Shooting assessments and nude body weights were completed before and after exercise to determine % body weight loss, accuracy, horizontal and vertical deviation, precision, aim time, and distance travelled by the point of aim. Results: Core temperature, HR, and PSI increased from rest (35.7 ± 4˚C; 88 ± 4bpm) in both cool (37.8 ± .5˚C; 143 ± 20bpm, 5.5 ±1.6) and hot (38.5 ± .4˚C; 167 ± 13 bpm, 7.8 ±1.11) conditions at 60 minutes but were significantly greater in hot compared to cool in the latter half of the trial. Percent body weight loss was greater in the hot (1.5 ± 0.5 %) compared to cool (0.9 ± 0.5 %) trials. Aim time decreased for cool (3.2 ± 0.4 sec) and hot (2.9 ±0.3 sec) trials compared to rest (4.1 ± 0.4 sec). Vertical-deviation increased in the kneeling position (15.2 ± 1.3 mm SE) compared to prone (10.7 ± 1.38 mm SE) but standing (14.1 ± 1.2 mm SE) was not significantly different from either. There were no changes from rest for accuracy, distance travelled, or precision in either hot or cool trials. Conclusion: Despite elevated levels of physiological strain there were no decrements in marksmanship performance due to exercise or heat stress. Kneeling may alter vertical deviation more than prone or standing shooting positions during marksmanship tasks. These data also indicate a need for more work related to prolonged, elevated PSI and/or % body weight losses commensurate with or exceeding the suggested 2% criteria

Physiological, perceptual and other performance decrements in combat related tasks following prolonged heavy-load marching

In response to challenging situations physiological and psychological adaptations result in elevated levels of arousal and when these levels are 'optimal' performance is enhanced. There are however, limitations to the amount of physiological and mental stimulation one can tolerate, with cumulative fatigue effects being the outcome when stressful conditions are imposed on the individual over an extended period of time. As a result of the extreme physical and cognitive demands placed on military forces while in combat, with soldiers being thrust into battle and required to make critical life-or-death determining decisions followed by appropriate motor responses, the physical and psychological capabilities of the troops are pushed to maximal limits, often resulting in undesirable decrements in physical and mental performance, with consequential human and materiel losses. Thirty-two soldiers participated in a battery of combat-related field and laboratory tests, first under 'normal' conditions with no prior physical activity and then immediately after the participation of an intensive bout of exercise. Physiological and perceptual responses plus standard of performance were measured at various stages of testing. Results of the Rating of Perceived Exertion (RPE), Body Discomfort Scale and heart rate responses revealed significantly higher levels of psychophysical strai,n in response to the strenuous physical activity. Despite these findings, the electromyographic (EMG) activity and efficiency of the combat-related skills were not negatively affected. Rather, nominal improvements in post-activity performance were noted, specifically response time, and this was attributed to elevated arousal and activation as a result of the exercise that was of sufficient duration to enhance arousal without imposing long term cumulative fatigue effects

Human load carriage : the ergonomic assessment and development of military load carriage systems

There were two main aims to the thesis: (1) to develop a mobile 'in-field' pressure measurement system to assess pressure at Body-Load Carriage System (LCS) interfaces (shoulders and hips). (2) To evaluate and compare prototype LCS designs in-field and to provide human factor requirements for design improvement. To satisfy the aims of the thesis in-field trials were carried out in a realistic military context. The purposes of these trials were to: (1) compare the standard issue British military LCS against a prototype LCS design in terms of pressure and subjective comfort; (2) increase the understanding of the properties of the shoulder and hip interfaces; (3) assess the relationship between loading at the shoulder and hip; and (4) identify whether other ergonomic issues are also important to consider. By assessing these areas human factors requirements for design were then determined. An additional (minor) aim was to develop a new prototype LCS with a greater degree of compatibility between the components of a military LCS (backpack and webbing), incorporation of material advances, and with a greater consideration for fit and posture. Four main experimental trials were performed the first (n = 11) assessedth e affect of clothing layers at the body-LCS interface on transmitted pressure. Results showed that clothing layers even worn in multiple have no effect on pressure transmission. Thus, no relief from pressure exists for the user. This highlighted the importance of the materials in the shoulder and hip straps. The second trial (n = 10) was a laboratory based comparison of two backpacks, the first the standard issue British military pack, the second a new prototype. Results found significant difference in subjective comfort and also peak pressure at the shoulder interface. The prototype backpack being associated with reduced peak pressure and increased comfort. The third trial (n = 10) assessed whole LCSs (backpack + webbing) in field with civilian participants. The standard issue LCS was compared against a prototype LCS. No significant difference in pressure was identified between the two LCSs, although differences in subjective comfort ratings were still significant indicating a preference for the prototype LCS. The final trial (n = 30) was military in-field trial. Military personnel and loadings were utilised. Again no significant difference in pressure data was identified although differences in subjective ratings remained significant with the prototype LCS design being preferred. Research findings highlighted the continued need for subjective assessment. The relationship between pressure loading at the shoulder and hip interfaces, along with locations of peak pressure within each interface were found to be important factors affecting comfort. Increased pressure distribution at the interfaces via new materials and design was also associated with increased comfort. Other areas which appeared important were the effect of posture and other physical forces not measured (i.e. shear and friction). Human factors guidelines were created for finiher LCS designs and future research ideas were presented.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Assessing Cognitive-Motor Interference in Military Contexts: Validity and Reliability of Two Dual-tasking Tests

Introduction Cognitive-motor interference is the decrease in cognitive performance and/or physical performance occurring when a cognitive task and a physical task are performed concurrently (dual task) compared to when they are performed in isolation (single task). The aim of this study was to investigate the construct validity and test–retest reliability of two cognitive-motor interference tests in military contexts. Materials and Methods Twenty-two soldiers, officers, and cadets performed a 10-min loaded marching, a 10-min Psychomotor Vigilance Task, and the two tasks combined (visit 1). During visit 2, a 5-min running time trial, a 5-min Word Recall Task, and the two tasks combined. These tests were repeated by 20 participants after 2 weeks (visits 3 and 4). Results Significant impairments were shown on both running distance (P < .001) and number of words recalled (P = .004) in the dual-task condition compared to the single-task condition. Significantly shorter step length (P < .001) and higher step frequency (P < .001) were found during the loaded marching in the dual-task condition compared to the single-task condition. No significant differences were observed in mean reaction time (P = .402) and number of lapses (P = .479) during the Psychomotor Vigilance Task. Good-to-excellent reliability was found for all the cognitive and physical variables in both single- and dual-task conditions, except for the number of lapses. Conclusion These findings suggest that the Running + Word Recall Task test is a valid and reliable dual-tasking test that could be used to assess cognitive-motor interference in military contexts