Subjective and objective evaluation of shoulder muscle fatigue

In order to relate EMG signs of localized muscle fatigue to subjectively perceived muscle fatigue, a study was undertaken on 20 healthy volunteers exposing their right trapezius muscle by raising the arm to 90° of abduction. Every person performed two contractions: 0 kg hand load during 5 min and 2 kg hand load during 2.5 min. Surface EMG was recorded and analysed with respect to RMS amplitude and mean power frequency (MPF). Subjective muscle fatigue was estimated with a psychophysical rating scale (Borg's CR-10 Scale). At high load level we found a significant correlation between MPF and the CR-scores (r = ? 0.46), but at low load level there was no correlation. At high load level there was a linear decrease of MPF with increasing load dose, but at low load level the MPF did not change, despite significant subjective fatigue. There was a linear rise of the CR-score with increasing load dose, more pronounced at high load level. It was concluded, that at low load levels common in working life, MPF and subjective scores seem to provide different fatigue information. Moreover, the MPF did not seem to work as a valid estimator of muscle fatigue at this low load level. Caution is recommended if it is to be used in static low-load situations.     

Influence of fatigue in neuromuscular control of spinal stability

Lifting-induced fatigue may influence neuromuscular control of spinal stability. Stability is primarily controlled by muscle recruitment, active muscle stiffness, and reflex response. Fatigue has been observed to affect each of these neuromuscular parameters and may therefore affect spinal stability. A biomechanical model of spinal stability was implemented to evaluate the effects of fatigue on spinal stability. The model included a 6-degree-of-freedom representation of the spine controlled by 12 deformable muscles from which muscle recruitment was determined to simultaneously achieve equilibrium and stability. Fatigue-induced reduction in active muscle stiffness necessitated increased antagonistic cocontraction to maintain stability resulting in increased spinal compression with fatigue. Fatigue-induced reduction in force-generating capacity limited the feasible set of muscle recruitment patterns, thereby restricting the estimated stability of the spine. Electromyographic and trunk kinematics from 21 healthy participants were recorded during sudden-load trials in fatigued and unfatigued states. Empirical data supported the model predictions, demonstrating increased antagonistic cocontraction during fatigued exertions. Results suggest that biomechanical factors including spinal load and stability should be considered when performing ergonomic assessments of fatiguing lifting tasks. Potential applications of this research include a biomechanical tool for the design of administrative ergonomic controls in manual materials handling industries.     

On the relationship between subjective and objective measures of fatigue

Objective: Objective and subjective methods have been used in the past to assess workplace fatigue, but little is known about correlations between them. We examine correlations between subjective and objective measures, including measures collected in a workplace scenario. Methods: 15 young and 17 older participants were assessed before and after work with four types of fatigue measure: objective physical (posturography), objective mental (psychomotor vigilance task), subjective physical and mental (self-assessment), objective and subjective realistic (oculomotor behaviour, observer-rated facial expression, typing performance). Results: Pre- and post-test scores were analysed with an ANOVA, significant differences were submitted to a factor analysis. It yielded three factors: one representing posturography, the second self-rated mental and physical fatigue and the third observer-rated facial expression. Conclusions: Results advocate the existence of three independent fatigue components: Objective physical fatigue, introspective and extrospective fatigue.

Practitioner Summary: This study analyses correlations between different subjective and objective fatigue markers to better understand the complex nature of workplace fatigue. Measurements were conducted directly at the workplace. Results reveal that fatigue comprises three independent fatigue components: Objective physical fatigue, introspective and extrospective fatigue.     

Comparison of visual fatigue caused by head-mounted display for virtual reality and two-dimensional display using objective and subjective evaluation

This study aimed to evaluate objective and subjective visual fatigue experienced before and after performing a visual task while using a head-mounted display for virtual reality (VR-HMD) and two-dimensional (2D) display. Binocular fusion maintenance (BFM) was measured using a binocular open-view Shack–Hartmann wavefront aberrometer equipped with liquid crystal shutters. Twelve healthy subjects performed the BFM test and completed a questionnaire regarding subjective symptoms before and after performing a visual task that induces low visually induced motion sickness (VIMS). BFM (p = .87) and total subjective eye symptom scores (p = .38) were not significantly different between both groups, although these values were significantly lower after the visual task than before the task within both groups (p < .05). These findings suggest that visual fatigue after using a VR-HMD is not significantly different from that after using a 2D display in the presence of low-VIMS VR content.

Practitioner summary: Objective and subjective evaluation of visual fatigue were not significantly different with the use of a head-mounted display for virtual reality (VR-HMD) and two-dimensional display. These results should be valuable not only to engineers developing VR content but also to researchers involved in the evaluation of visual fatigue using VR-HMD.

Abbreviations: VR: virtual reality; VR-HMD: head-mounted display for virtual reality; BFM: binocular fusion maintenance; BWFA: binocular open-view Shack–Hartmann wavefront aberrometer     

Perceived fatigue after mental work: an experimental evaluation of a fatigue inventory

The aim of this study was to investigate the perceived fatigue after mental work and to test the Swedish Occupational Fatigue Inventory (SOFI). Twenty male and 20 female participants worked with proof reading (2 x 90 min) and a vigilance task (2 x 60 min). After each task session, perceived fatigue was rated with the SOFI and Borg's CR10O-scale. In addition, physiological reactions were registered; blood pressure, heart rate, heart rate variability and muscle activity in corrugator supercilii, as well as measures of performance: reaction time, number of pages read and number of proof errors found, number of detected signals. As expected, the highest ratings were obtained on Lack of energy, Lack of motivation and Sleepiness, particularly after the vigilance task. High ratings after both work tasks were also found on the CR10-scale. Men and women did not differ significantly with respect to their ratings. No clear-cut physiological reactions were found to correlate with ratings of fatigue. The results indicate the validity of the mental dimension of the SOFI.     

Perceived fatigue after mental work: an experimental evaluation of a fatigue inventory

The aim of this study was to investigate the perceived fatigue after mental work and to test the Swedish Occupational Fatigue Inventory (SOFI). Twenty male and 20 female participants worked with proof reading (2x90 min) and a vigilance task (2x60 min). After each task session, perceived fatigue was rated with the SOFI and Borg's CR10-scale. In addition, physiological reactions were registered; blood pressure, heart rate, heart rate variability and muscle activity in corrugator supercilii, as well as measures of performance: reaction time, number of pages read and number of proof errors found, number of detected signals. As expected, the highest ratings were obtained on Lack of energy, Lack of motivation and Sleepiness, particularly after the vigilance task. High ratings after both work tasks were also found on the CR10-scale. Men and women did not differ significantly with respect to their ratings. No clear-cut physiological reactions were found to correlate with ratings of fatigue. The results indicate the validity of the mental dimension of the SOFI.     

Development and initial assessment of objective fatigue measures for apple harvest work

Previous research has shown that neck, back and shoulder musculoskeletal strain is a major occupational health problem affecting migrant orchard harvest workers. Researchers seek to measure the effect of an ergonomic modification to the apple picking bucket on muscle fatigue, however objective measures for use in the orchard are not yet available.

The purpose of this study is to develop simple back, shoulder or arm strength measures, which detect statistically significant drops in strength over one workday. Candidate muscle strength measures were piloted in the laboratory, adapted for the orchard and evaluated (n=102). Data were analyzed for morning to afternoon fatigue, and for correlation between fatigue score and hours worked.

In the laboratory, the timed arm hold (35.7% time reduction, 95% CI: 21.81–49.61), and the timed spinal extension (31.8% time reduction, 95% CI: 23.54–39.96) showed significant fatigue. In the orchard (n=102), only the timed arm hold showed significant (11.4%, p<.0001) fatigue. The potential effect of field conditions and subject motivation on these results needs further exploration.     

球员效率值(PER)算法的Mysql实现与应用

在篮球比赛中,统计数据可以反映一名球员的能力,但不一定全面、客观,通过对统计数据进行处理与修正可以更客观地评估篮球运动员的个人能力。使用MySql数据库实现了PER算法;选取有代表性的几名球员的PER值与hoopdata.com网站给出的PER值进行比较,然后将PER算法应用于CBA联盟2012-2013赛季中。     

Influence of fatigue time and level on increases in postural sway

The purpose of this study was to investigate the influence of fatigue time and fatigue level on the increases in postural sway during quiet standing. Centre of pressure-based measures of postural sway were collected both before and after fatiguing participants using three different fatigue levels and two different fatigue times. Results showed increasing fatigue time increased sway velocity and sway area, and increasing fatigue level increased sway velocity. Fatigue time effects are important to consider when applying laboratory-based findings to the field given that the fatigue time can differ substantially between the two. Fatigue level effects imply a dose – response relationship between localized muscle fatigue and risk of falling that can have important implications in work/rest cycle scheduling for occupations at risk of injurious falls.     

Influence of fatigue time and level on increases in postural sway

The purpose of this study was to investigate the influence of fatigue time and fatigue level on the increases in postural sway during quiet standing. Centre of pressure-based measures of postural sway were collected both before and after fatiguing participants using three different fatigue levels and two different fatigue times. Results showed increasing fatigue time increased sway velocity and sway area, and increasing fatigue level increased sway velocity. Fatigue time effects are important to consider when applying laboratory-based findings to the field given that the fatigue time can differ substantially between the two. Fatigue level effects imply a dose - response relationship between localized muscle fatigue and risk of falling that can have important implications in work/rest cycle scheduling for occupations at risk of injurious falls.     

Design and evaluation of a gamified system for ERP training

Enterprise Resource Planning Systems (ERP) facilitate the flow of information within a company by storing data in common databases. These systems offer a holistic view of the organization because they reduce information redundancy, offer information in real time, help with process standardization, and improve information flow and communication among employees. Nevertheless, the benefits attributed to an ERP implementation can be lost without an effective user training. Previous studies have observed that common training mechanisms don't provide meaningful learning to users, and that user satisfaction rates range from neutral to low. Therefore, in this paper we study the effects that gamification has on ERP training concerning user learning and user satisfaction. Gamification is the use of game elements and game design techniques in non-gaming environments. Several applications prove that gamified systems increase user engagement and performance. Our hypotheses were that a gamified system for ERP training improve user learning and user satisfaction levels during the training period. To test our hypotheses, we designed and evaluated a gamified system. The results showed that users trained using a gamified system performed better than those trained using a conventional, non-gamified, training mechanism.     

网络性能评估中客观权重确定方法比较

针对目前网络性能评估中多元指标之间权重难以客观确定的问题,将标准差法、离差最大化法、熵权法以及它们的改进算法应用于客观权重确定,使客观权重确定方法的选择更加全面完备.改进算法引入指标间冲突性概念,考虑指标间相关性对客观权重确定的影响.以VOIP网络为例,采用仿真方法获取权重计算样本,为了选取更加客观的权重确定方法,将六种权重计算方法进行了比较.测试结果表明,基于指标相关性的指标权重确定方法(CRITIC)计算出的权重具有较强客观性.     

The differences in motivations of online game players and offline game players: A combined analysis of three studies at higher education level

Computer games have become a highly popular form of entertainment and have had a large impact on how University students spend their leisure time. Due to their highly motivating properties computer games have come to the attention of educationalists who wish to exploit these highly desirable properties for educational purposes. Several studies have been performed looking at motivations for playing computer games in a general context and in a Higher Education (HE) context. These studies did not focus on the differences in motivations between online and offline game players. Equally the studies did not look at the differences in motivations of people who prefer single player games and people who prefer multiplayer games. If games-based learning is to become a recognised teaching approach then such motivations for playing computer games must be better understood. This paper presents the combined analysis of three studies at HE level, performed over a four year period from 2005 to 2009. The paper focuses on differences of motivations in relation to single player/multiplayer preference and online/offline game participation. The study found that challenge is the top ranking motivation and recognition is the lowest ranking motivation for playing computer games in general. Challenge is also the top ranking motivation for playing games in HE while fantasy and recognition are the lowest ranking motivations for playing games in HE. Multiplayer gamers derive more competition, cooperation, recognition, fantasy and curiosity from playing games and online gamers derive more challenge, cooperation, recognition and control from playing games. Multiplayer gamers and online gamers ranked competition, cooperation and recognition significantly more important for playing games in HE than single players and offline participants.     

Evaluation of physiological work demands and low back neuromuscular fatigue on nurses working in geriatric wards

This study evaluated the physiological demands and low back neuromuscular fatigue patterns following a daytime work shift of 21 female nurses working in geriatric wards. Subjects' heart rate (HR) at work was monitored for 8 h and surface electromyogram (EMG) of their back muscle was recorded during a 1-minute horizontal trunk holding test before and after work. Results showed that the nurses had heart rates exceeding 90 beats/min in 57% and 110 beats/min in 19% of their working hours. The EMG revealed a significant drop in initial median frequency (MF) (p = 0.04) and increase in negative slope of the MF/time plot (p<0.001) of the back muscle after work. These suggest that the muscles were fatigued after work. The nurses rated patient lifting, transfer and turning as most physically demanding, and these corresponded to the highest heart rates recorded. The physiological and neuromuscular strain on the nurses indicated that extreme care should be exercised at work, particularly towards the end of a work shift when the muscles have become fatigued.     

The effect of physical training on objective and subjective measures of productivity and efficiency in industry

The aims of this study were to investigate the associations between an activity logbook and the RT3 accelerometer and to assess whether the RT3 can discriminate activity levels in healthy adults. Ten participants completed two trials wearing an RT3 accelerometer over a 4–6 h period and completed a detailed activity log. Results showed a poor correlation between the RT3 in moderate activities (r = 0.22) in comparison to low (r = 0.52) and hard (r = 0.70) from the logbook. A significant difference was found in average RT3 vector magnitude (VM) counts/min in each activity level (p < 0.0001). Discriminant analysis demonstrated that an RT3VM counts/min value of approximately 500 was found to have high sensitivity (88%), and specificity (88%) for discriminating between low and moderate activity levels from the logbook. This study found that accelerometry has the potential to discriminate activity levels in free living. This study is the first to investigate whether tri-axial accelerometry can discriminate different levels of free-living activity recorded in an activity logbook. The RT3 accelerometer can discriminate between low and moderate physical activities and offers a methodology that may be applicable to future research in occupational settings.     

Empirical evaluation of training and a work analysis tool for participatory ergonomics

A controlled laboratory experiment was performed to test the effects of ergonomics training and the NIOSH lifting equation on the participatory redesign of a simulated manual material handling job. Before performing the job, 16 subjects were given ergonomics training and 16 were instructed on how to use the NIOSH lifting equation for manual lifting tasks. Compared to a control group, subjects who received the ergonomics instruction identified and eliminated more risk factors in the simulated job. While subjects who used the NIOSH lifting equation also identified more risk factors, they did not eliminate any more risk factors than the control group. No additive benefit was found using both the training and the lifting equation over either method alone. Ergonomics training led to better improvements than use of the lifting equation in terms of risk factors identified and eliminated. Implications for use of training and tools in participatory ergonomics approaches are discussed.

Relevance to industry

This study supports that ergonomics training should be a requisite for any participatory ergonomics approach. Given a fundamental level of ergonomics training, subjects demonstrated that they were better capable of identifying and eliminating risk factors in the job.     

Fitness inheritance in multiple objective evolutionary algorithms: A test bench and real-world evaluation

In many real-world applications of evolutionary algorithms, the fitness of an individual has to be derived using complex models and time-consuming computations. Especially in the case of multiple objective optimisation problems, the time needed to evaluate these individuals increases exponentially with the number of objectives due to the ‘curse of dimensionality’ [J. Chen, D.E. Goldberg, S. Ho, K. Sastry, Fitness inheritance in multi-objective optimization, in: W.B. Langdon et al. (Eds.), GECCO 2002: Proceedings of the Genetic and Evolutionary Computation Conference, July 9–13, Morgan Kaufmann Publishers, New York, 2002, pp. 319–326]. This in turn leads to a slower convergence of the evolutionary algorithms. It is not feasible to use time-consuming models with large population sizes unless the time to evaluate the objective functions is reduced. Fitness inheritance is an efficiency enhancement technique that was originally proposed by Smith et al. [R.E. Smith, B.A. Dike, S.A. Stegmann, Fitness inheritance in genetic algorithms, in: Proceedings of the 1995 ACM Symposium on Applied Computing, February 26–28, ACM, Nashville, TN, USA, 1995] to improve the performance of genetic algorithms. Sastry et al. [K. Sastry, D.E. Goldberg, M. Pelikan, Don’t evaluate, inherit, in: L. Spector et al. (Eds.), GECCO 2001: Proceedings of the Genetic and Evolutionary Computation Conference, Morgan Kaufmann Publishers, San Francisco, 2001, pp. 551–558] and Chen et al. [J. Chen, D.E. Goldberg, S. Ho, K. Sastry, Fitness inheritance in multi-objective optimization, in: W.B. Langdon et al. (Eds.), GECCO 2002: Proceedings of the Genetic and Evolutionary Computation Conference, July 9–13, Morgan Kaufmann Publishers, New York, 2002, pp. 319–326] have developed analytical models for fitness inheritance. In this paper, the usefulness of fitness inheritance for a set of popular and separable multiple objective test functions as well as a non-separable real-world problem is evaluated based on unary performance measures testing closeness to the Pareto-optimal front, uniform distribution along and extent of the obtained Pareto front. A statistical evaluation of the performance of an NSGA-II like algorithm on the basis of these unary performance measures suggests that especially for non-convex or non-continuous problems the use of fitness inheritance negatively affects the closeness to the Pareto-optimal front.     

Specification and evaluation of level of detail selection criteria

Level of detail (LOD) is a technique where geometric objects are represented at a number of resolutions, allowing the workload of the system to be based upon an object's distance, size, velocity, or eccentricity. However, little is known about how to specify optimally when a particular LOD should be selected so that the user is not aware of any visual change, or to what extent any particular LOD scheme can improve an application's performance. In response, this paper produces a generic, orthogonal model for LOD based upon data from the field of human visual perception. The effect of this model on the system is evaluated to discover the contribution that each component makes towards any performance improvement. The results suggest that both velocity and eccentricity LOD should be implemented together (if at all) because their individual contribution is likely to be negligible. Also, it is apparent that size (or distance) optimisations offer the greatest benefit, contributing around 95% of any performance increment.