460 research outputs found

    Cross-Limb Dynamics of Postural Tremor Due to Limb Loading to Fatigue: Neural Overflow but not Coupling

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    Many experiments have shown independence of the index finger dynamics under bilateral postural tremor protocols. Here we investigated in young adults the dynamics of bilateral multidirectional postural tremor and forearm muscle activity under the progressively fatiguing conditions supporting an external weight to the point of induced postural failure. When no loads were applied, tremor in the vertical (VT) and mediolateral (ML) directions was similar with prominent peaks within 2- to 4-Hz and 8- to 12-Hz bandwidths. Contrastingly tremor in the anterior-posterior (AP) direction was characterized by a single peak between 0 and 2 Hz. Although no tremor coupling occurred cross limbs, strong within-limb coupling was found between ML and VT directions when no loads were applied (coherence range: 0.77-0.85), implying that these oscillations are related and likely derived from mechanical sources. Applying an external load to the index finger(s) led to significant increases in the amplitude of VT tremor and EMG activity within that limb but also caused increases in tremor directions not aligned with the gravitational vector (AP and ML). Significant increases in VT and ML tremor and EMG activity in the contralateral (unloaded) limb were also found when a single index finger was loaded; however, this bilateral increase did not align with increases in interlimb coupling (coherenc

    Factors Influencing Police Officer Marksmanship During Qualifying Drills

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    Police departments across the country are interested in reducing the costs of retraining and improving the rate of retention of the officers they are training. If police officers can be better trained in the skills necessary for marksmanship due to improved evaluative methods by instructors then the rate of progression in skill development could be accelerated. The purpose of this non-experimental, exploratory (comparative) and explanatory (correlational) survey research was to examine the relationships among demographics, handgrip, firearms experience, physiological changes, environmental factors, and psychological state for police officers during qualifying shooting drills, and to determine if Marksmanship during qualifying shooting drills differed among police officers according to those relationships. In addition, to determine if demographics, police experience, firearms experience, handgrip, physiological changes, and environmental factors were significant explanatory variables of the Psychological State of police officers during qualifying shooting drills; and to determine if demographics, police experience, firearms experience, psychological state, handgrip, physiological changes, and environmental factors were significant explanatory variables of Marksmanship during qualifying shooting drills for police officers. Three hundred and three officers agreed to participate in the study. Of the officers who chose to participate, 242 were male and 61 were female, 169 were Hispanic, 133 were non Hispanic, and two did not specify their ethnicity. Independent t-tests or ANOVA with post hoc comparisons to compare differences in marksmanship score and stepwise multiple regression analyses were conducted to answer research questions and hypotheses. In addition, all measures were examined for reliability and validity. Exploratory factor analysis was conducted on the State Trait Anxiety Inventory (STAI) and resulted in three subscales (Calmness, Anxiety, Nervous/Jittery/Indecisive) and a 19 item revised STAI. Findings indicated that (a) the age of police officers provided a trend explanatory variable of the Calmness subscale of the STAI; (b) the demographics of gender and age, in addition to police experience, provided a significant explanatory model of anxiety in police officers. Older male officers with more experience had more anxiety; (c) the demographics of gender and age, in addition to firearms experience (military experience) provided a significant explanatory model of the Nervous/Jittery/lndecisiveness subscale of the STAI; (d) the demographic of age provided a significant explanatory variable of the total 19-item scale. The best explanatory variables of marksmanship included race, handgrip strength, gender, ethnicity, temperature, blood pressure changes, and humidity. The range of variance in the best model was 11.4% to 13.5%. This indicated that white, Hispanic officers, with stronger dominant handgrip, cooler ambient temperature, lower humidity and with smaller changes in systolic blood pressure had higher marksmanship scores during qualifying shooting drills. Future researchers should conduct similar studies with populations from other regions around the country and the world in order to strengthen the external validity of findings

    Pre-employment functional capacity assessment and remedial intervention program for the New South Wales police

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    Assessment of physical capacity prior to employment serves a vital function in ensuring police recruits have the physical capability to perform essential policing functions. In the past, law enforcement agencies have used a variety of physical assessments to exclude potential candidates. The assessment criterion that has been used has lacked appropriate validation with critics arguing that the tests are invalid, irrelevant and potentially discriminatory. Additionally, the tests that have been used have focused on the assessment of policing specific skills prior to any skill-based training. For many years, sports scientists have used physiological assessments to identify specific weaknesses in the performance capability of athletes. The individual physiological assessments that are utilised are chosen to assess the functional components of the sport concerned. The results of these assessments are used to develop an effective remedial intervention program resulting in increased sports performance. This same concept can also be applied to a police training and recruitment program. The general aim of this study was to develop a pre-employment functional capacity assessment program that can accurately predict inadequate performance capability as well as determining specific weaknesses in underlying physiological capacity. This allows potential recruits who have less the

    Effects of local muscle temperature manipulations on neuromuscular function

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    Human muscle can operate through a wide range of temperature; however optimal function may occur throughout a much narrower range. Muscle cooling results in an impairment in muscle contractile properties and maximal force, whereas heating the muscle fosters faster and more powerful contractions. However, what neural compensatory mechanisms exist such that the muscle can still function adequately throughout a wide range of temperatures are unknown and forms the purpose of this dissertation. To this end, muscle contractile and motor unit properties of the flexor carpi radialis were examined during three separate projects involving forearm temperature manipulations. Chapter 4 investigates the effects of local forearm cooling on motor unit properties during an isometric wrist flexion contraction to 50% of baseline maximal force. Chapter 5 builds upon Chapter 4 to include local heating and contraction intensities above and below the motor unit recruitment range of the flexor carpi radialis. Finally, Chapter 6 investigates how different muscle temperatures affect manual performance – assessed through a staircase isometric force tracking task. Local cooling did not affect the ability to perform voluntary contractions to 50% of baseline force, but motor control was achieved through changes in the relationship between motor unit firing rate and recruitment threshold, indicating either faster motor unit firing rates and/or earlier motor unit recruitment to accomplish a task at the same absolute force (Chapter 4). However, these differences were not present when force requirements were made relative to muscle capacity of the respective temperature conditions. We found that motor units were recruited earlier in the cold when contraction intensity was above the motor unit recruitment range (Chapter 5). The altered relationship between motor unit firing rate and recruitment threshold observed in Chapter 4 with muscle cooling at an absolute force level did not affect isometric force tracking ability (Chapter 6). Collectively, this thesis found that the motor unit recruitment threshold may be depressed in the cold due to cutaneous stimulation, and that manual function during an isometric force tracking task involving relatively light loads is not impaired with muscle temperature changes

    Physical and Performance Characteristics May Influence Successful Completion of Military Tasks on the Sandhurst Competition

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    Identification and development of physical characteristics that lead to efficient performance of military skills or tasks has been a consistently difficult task for the United States military for decades. The literature suggests certain physical characteristics may be more important, although this information is conflicting. Furthermore, the military physical fitness training program that is intended to prepare soldiers for combat is commonly evaluated with the Army Physical Fitness Test (PFT), a test that is more suited for evaluating health and wellness rather than task-specific fitness. All of this testing and training of soldiers focuses on the individual soldiers and their abilities although military skills or tasks are seldom if ever conducted independently. The first purpose of this dissertation was to identify relationships between the PFT, anthropometrics, measures of strength, and power. The second purpose was to identify the team characteristics that influence team performance during the Sandhurst Competition (a 2-day simulated military operation). Strong correlations were found between PFT events and weak correlations were found between PFT measures and evaluations of strength and power. The strong correlations between PFT events could indicate that only one event may be necessary to determine health and wellness. The weak correlations between events of the PFT and measures of strength and power suggest the PFT is not an assessment of strength and power based on the strength and power measures employed in the current study. The evaluation of team characteristics indicated that age (possibly experience) had the largest effect on Sandhurst Competition performance. Further analysis of each event supported the contention that age influences performance but also identified specific aerobic, anaerobic, and anthropometric variables that influenced performance on particular events. The data from this dissertation suggests that teams competing in the Sandhurst Competition should attempt to recruit team members with more experience, very high run scores, and high vertical jump heights

    EFFECT OF LOAD CARRIAGE ON TACTICAL PERFORMANCE

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    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

    THE EFFECTS OF AGING ON MULTIPLE POSTURAL MUSCLE CONTROL AND POSTURAL SWAY BEHAVIOR

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    Episodes of instability and falls in the elderly represent a major public health concern. The lack of scientific information about the effects of age-related changes on neurophysiological mechanisms of postural control has limited the advance in the field of fall prevention and rehabilitation of balance disorders. The overall goal of this dissertation was to investigate the effects of aging on postural control. Considering the progressive non-homogeneous deterioration of aging physiological systems, a series of five experimental studies, with healthy young and healthy nonfaller older adults performing upright stance tasks, explored three main hypotheses: (1) intermuscular coherence analysis is able to detect signs of intermuscular synchronization at lower frequency bands as one of the strategies used by the Central Nervous System to control upright stance; (2) aging is associated with a reorganization of correlated neural inputs controlling postural muscles; and (3) aging is associated with changes in body sway behavior. The first three studies corroborated the use of intermuscular coherence analysis to investigate the formation of correlated neural inputs forming postural muscle synergies during upright stance. The fourth study revealed an age-related reorganization of the distribution and strength of correlated neural inputs to multiple postural muscles. Healthy nonfaller older adults presented stronger levels of synchronization, within 0–10 Hz, for three distinct muscle groups: anterior, posterior, and antagonist muscle groups. The fifth study investigated age-related changes on postural sway using traditional and novel postural indices extracted from the center of pressure coordinates. Although the functional base support is preserved in healthy nonfaller older adults, these seniors revealed a larger, faster, shakier, and more irregular pattern of body sway compared to healthy young adults. In addition, age-related changes on supraspinal mechanisms, spinal reflexes, and intrinsic mechanical properties of muscles and joints involved in postural control were observed by changes in both rambling and trembling components of the postural sway. Findings reported here provide valuable information regarding compensatory mechanisms adopted by healthy nonfaller older adults to control upright stance. Together, these findings suggest an age-related reorganization of correlated neural inputs controlling multiple postural muscles, accompanied by changes in body sway behavior

    Fatigue at the Workplace: Measurement and Temporal Development

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    Fatigue at the workplace has been described as a multidimensional construct, affecting the overall state of the whole organism, which may be a consequence of prolonged work and various psychological, socioeconomic, and environmental factors. In the short term, fatigue may lead to discomfort, diminished motor control, reduced proprioception, increased force variability, and reduced strength capability, resulting in reduced performance, lowered productivity, deficits in work quality, and increased incidence of accidents and human errors. Fatigue may also lead to longer-term adverse health outcomes such as chronic fatigue syndrome, myalgia, and burnout syndromes, and may be a precursor to WMSDs – work-related musculoskeletal disorders. If indeed fatigue is a precursor to WMSDs and other long-term health outcomes, it may then be a relevant biomarker for cumulative exposure to repetitive and/or sustained work, and thus a useful risk indicator and/or a design and evaluation tool. However, little is known of the temporal pattern of fatigue development and its relationships with disorder risks and work performance. The objective of this thesis was to identify and evaluate a battery of fatigue measures for both laboratory and field-based research, and provide insight into fatigue development in work-relevant task conditions. Six studies were designed to address these objectives. In the first study, measures and analysis methods that detect fatigue-related changes were identified by a group of expert fatigue researchers. The second was an exploratory study focused on the responsiveness of a select number of measures during a workday and multiple workdays in realistic physically demanding residential plumbing work. In the third study, a selected number of conventional and novel measures were evaluated for their reliability and sensitivity in a controlled laboratory setting. This study also addressed the responsiveness of measures during a test battery or during the fatiguing activity (i.e., continuously), and the time between cessation of activity and test battery in which measures remain responsive. The fourth study reported on whether circadian effects were detectable by selected measures, providing insight towards the daylong reliability of these measures. In the fifth study, measures were evaluated in four fatiguing conditions, representing changes in type of contraction, intensity, and body segment. Furthermore, the pattern of fatigue development and the temporal responsiveness of measures were described. Finally, measures were assessed over an 8-hour light precision micropipetting task to investigate temporal responsiveness of measures and fatigue development. Errors were quantified and the effects of scheduled work breaks were reported. In study 1, fifty-seven measures were identified based on outcomes and/or effects of fatigue in the workplace. Based on the perceived validity, reliability, and practicality in laboratory and field investigations, four measures were recommended for both settings: maximum voluntary contractions, questionnaires and fatigue scales, Borg’s rating of perceived exercise or discomfort, and visual analog scales. On the other hand, twenty-five measures were not recommended for field studies, including methods traditionally recognized as “gold standard” in measuring cellular and metabolic changes. In study 2, fatigue was documented in realistic physically demanding work while employing a set of measures to provide a comprehensive picture of fatigue development. Not all measures revealed increasing fatigue over the workday or over the workweek, which may be a result of measures reflecting different fatigue processes. Thus, the study reinforced the need of a complementary set of measures, reflecting multiple domains, to measure and interpret the temporal development of fatigue. Two measures, rating of perceived discomfort and grip strength, indicated significant differences within a work day, notably an increase at the beginning and end of the shift (perceived discomfort) and a decrease between mid-shift and end of shift (grip strength). It was speculated that within-day trends were consistent with central fatigue mechanisms. Over multiple workdays, both central and peripheral components displayed a significant day effect. Fatigue accumulation over the workweek was observed with grip strength, physiological resting tremor, and postural tremor measures, particularly between day 1 (Tuesday) and day 4 (Friday). In study 3, test-retest reliability ranged between “poor agreement” and “almost perfect agreement”. In terms of sensitivity, action tremor, MMG RMS amplitude, postural tremor, and rating of perceived fatigue were highly responsive. Perceived fatigue remained elevated, relative to baseline, until 11 minutes post-exercise. Postural and physiological tremor persisted from baseline until the third minute of recovery. Action tremor, however, quickly recovered within the first minute of recovery. This current study found that for most of the measures, there were no statistical differences between test battery and continuous measurement, but a few measures were approaching statistical significance. Action tremor and mechanomyography collected during a test contraction, and perceived fatigue assessed by a visual analog scale, were found to be most reliable, most responsive, comparable to continuous measures, and sensitive after the fatiguing activity, and should be considered with other measures of interest, as part of a test battery. In study 4, only two measures revealed a statistically significant time-of-day effect: mechanomyography of a flexor forearm muscle and action tremor at 30% MVC. These two measures exhibited rhythmicity based on cosinor analysis. Therefore a degree of caution might be required when interpreting daylong fatigue with these two measures, whereas the other measures may not be susceptible to, or detect, significant diurnal effects. Although the remaining measures did not reveal statistically significant time effects, most measures were characterized with similar patterns to those found in previous literature. In study 5, there was no one universal measure that was common, in terms of responsiveness, in all exercise conditions. Although no single measure was found to be most responsive in all conditions, there were measures responsive in most exercise conditions as either a continuous or test battery measure. This was the case with action tremor. A maximum voluntary contraction, which is dependent on processes in both central and peripheral domains, was similarly responsive. Rating of perceived fatigue, which has been cited as a centrally mediated indicator, was also found to increase with exercise progression in hand conditions. Therefore fatigue measures, reflecting changes to both central and peripheral processes, may be useful in measuring tasks and exercises of varying parameters. In this study, we support earlier investigations on the pattern of fatigue development in isometric and time-varying (e.g., intermittent isometric, concentric) contractions. The temporal responsiveness of central and peripheral measures, on the other hand, may be a better reflection of the intensity of the task. The shoulder intermittent condition was not consistent with the expected pattern for an intermittent isometric contraction. However, the study protocol may have inadvertently generated lower muscle activity, and therefore the extent of fatigue may have been minimal. There remains a need to understand complex combinations of task-dependent factors in both fatigue development and temporal responsiveness. In study 6, nine measurement parameters revealed significant increases in fatigue over the work period. Traditional field measures (i.e., MVC and EMG) did not lead to extraordinary time effects. Error rates followed similar trends to the 9 significant measurements: an increase from baseline towards mid-morning, a slight decrease prior to the lunch break, a nadir after lunch, and increasing fatigue effects over the course of the afternoon. Error rates, however, might not be a sole consequence of fatigue – cognitive and physical; but might also reflect changes in arousal level. Over the pipetting task, there was interplay between peripheral and central fatigue mechanisms in three body segments: thumb, hand, and shoulder. Fatigue developed at a “local” level (i.e., at the three body segments) and was consistent with expected patterns observed in study 5, particularly if thumb and shoulder actions were considered concentric actions and the grip force was a sustained isometric contraction. Overall, the collective assessments suggested that rating of perceived fatigue and action tremor, on average, were highly repeatable and responsive in multiple task conditions. Postural tremor or steadiness and maximum voluntary contractions were moderately reliable and responsive. Different forms of tremor may be responsive to different task conditions. Postural tremor amplitude was found to increase over the course of an 8-hour workday in a light precision work task, and over multiple days in physically demanding work. Action tremor, on the other hand, appeared to be responsive at higher work intensities performed at a shorter duration of time. Possibly, action tremor may be more indicative of changes in the periphery, whereas postural tremor reflects changes more central in nature. Consequently, these measures should be considered for inclusion into a test battery for field use. For the ergonomist or health and safety practitioner, this body of work provides some insight into the utility of a test battery of fatigue measures to complement current task analysis techniques. For workplace researchers, this dissertation provides insight into the temporal development of fatigue in various task conditions and the reliability and responsiveness of select measures in both short and longer-term work-studies. This research might subsequently elicit future investigations in the relationship between work exposure, fatigue development, and performance and longer-term health outcomes
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