The influence of task variation on manifestation of fatigue is ambiguous – a literature review

Task variation has been proposed to reduce shoulder fatigue resulting from repetitive hand–arm tasks. This review analyses the effect of task variation, both ‘temporal (i.e. change of work–rest ratio)’ and ‘activity (i.e. job rotation)’ variation, on physiological responses, endurance time (ET) and subjective feelings. Pubmed was searched and complemented with references from selected articles, resulting in 17 articles. Temporal variation had some positive effects on the objective parameters, as blood pressure decreased and ET increased, and on the subjective feelings, as perceived discomfort decreased. The observed findings of activity variation showed both positive and negative effects of increased activity variation, while hardly any effects were found on electromyography manifestations of fatigue. In conclusion, the evidence for positive effects of increasing the level of variation is scarce. The number of studies on variation is limited, while in most studies the findings were not controlled for the amount or intensity of work.     

Examining desensitization using facial electromyography:Violent videogames,gender, and affective responding

The results of research investigating the effects of violent videogames have been inconsistent. Some evidence suggests that exposure to violent videogames decreases physiological arousal and results in desensitization to subsequent exposure to violent stimuli. Other research does not support these findings. This study examined physiological and affective desensitization to violent videogame play. Participants played a violent or non-violent videogame and then viewed aggressive, pleasant, and neutral images. Participants’ negative affect in response to the images was assessed by examining activity in the brow muscle region (i.e., corrugator supercilii), heart rate (HR), self-reported affect, and self-reported arousal. Based on previous research regarding the General Aggression Model (GAM), we expected that participants who played the violent videogame would demonstrate desensitization as evidenced by less reactivity in the corrugator supercilii region and less HR reactivity in response to violent images than participants who played the nonviolent videogame. We also expected that participants who played the violent videogame would rate the aggressive images as less aversive than those who played the nonviolent game. Contrary to our expectations, the findings were not consistent with the hypotheses based on the GAM.     

Evaluation of the loading of neck and shoulder musculature in overhead pushing and pulling exertions

Despite substantial epidemiological evidence relating overhead exertions with work‐related musculoskeletal disorders (WMSD) of the neck, effects of such exertions on the loading of neck or cervical spine musculature are not well understood. In this study, the effects of overhead pushing and pulling exertions on the loading of the cervical spine were evaluated using electromyography (EMG) and subjective discomfort ratings. Additionally, the role of gender as well as individual strength on the loading of neck musculature during such exertions was evaluated. Twenty‐four healthy individuals (12 men and 12 women) participated in this study. Each participant performed overhead pushing and pulling exertions, exerting 25%, 50%, and 75% of their respective maximum strengths. Overhead pushing exertions were found to be significantly more strenuous to the neck musculature than were the pulling exertions. Gender had no significant effect on the activities of the neck muscles. Participants with high strength, however, were able to exert more force at comparatively low muscle activation levels. Subjective discomfort ratings were strongly correlated with the EMG data. At various workplaces, avoiding overhead exertions is rather impossible due to material, interface, and site constraints. Based on the results of this study, however, during such exertions, an interchange between directions of force application could prevent sustained loading of the neck muscles, fatigue, and consequently the probability of neck WMSD incidents. © 2011 Wiley Periodicals, Inc.     

The influence of mental load on muscle tension

We examined the differences in muscle tension and in physiological measures depending on the type of mental task. Fifteen participants performed tests for sustained attention, vigilance and maintaining posture only. We analysed electromyogram (EMG) measures of extensor digitorum (ED), flexor carpi ulnaris (FU), deltoideus (DE) and trapezius (TR), and heart rate (HR) and respiratory frequency (RF). Measures indicated higher values for mental tasks than for maintained posture only with significant differences in all measures. The following relationships were also significant: between DE and physiological measures (HR and RF), between ED and the amplitude of EMG of the other three muscles, between FU and TR and between HR and RF. The results of this study showed that the relationship between mental demands and muscle tension was mostly reflected by tension in the arm and shoulder girdle muscles and, to a lesser degree, in forearm muscles.

Practitioner Summary: We focused on physiological and muscle tension measures differentiating work according to the level of mental demands. Differences in sustained attention, vigilance and maintaining posture only proved that mental demands were mostly reflected by tension in arm and shoulder girdle muscles and, to a lesser degree, in forearm muscles.     

Co-acting strangers but not friends influence subjective liking and facial affective responses to food stimuli

In recent years, consumers' emotional responses have been found to be an important complement to sensory and hedonic evaluations for the prediction of food choice and consumption behaviour. Given this trend, it is essential that the influence of contextual variables on emotion are investigated. The present study contributes to the discussion with an investigation of the effect of social context on implicit emotional responses to food images. 87 participants (56 female, 31 male) viewed food images of varying acceptability either alone, with a stranger, or with a friend. Subjective liking ratings were measured using a labelled affective magnitude scale, and facial muscle activity from zygomaticus major (contracted during smiling), corrugator supercilii (contracted during frowning) and levator labii superioris (contracted during nose wrinkling) were measured with an EMG recording system. Controlling for individual differences in facial expressivity and food image acceptability using linear mixed models, it was found that the presence of a co-acting stranger facilitated muscle activity indicative of a disgust response, increased the strength of relationship between muscle activity and subjective liking ratings, and led to lower subjective liking overall. No differences in muscle activity or subjective liking were found between subjects who participated alone and with a co-acting friend. This suggests that the influence of social context is complex, where the relationship between the subject and the social environment can impact both hedonic and emotional evaluations of food stimuli. These findings indicate that facial EMG can be a useful dynamic and implicit measure of emotion in consumer research, but it is critical to consider the social context of the testing environment.     

sEMG识别控制系统在虚拟仪器平台上的实现

在开发传统的sEMG识别控制系统时,一般采用软件算法研究与硬件实现相分离的方法,容易造成识别控制算法的“理想化”.设计一种基于虚拟仪器的sEMG识别控制系统,该系统平台基于LabVIEW及数据采集设备、MATLABScrip节点程序和机械臂执行机构,实现了对sEMG识别控制系统的半实物仿真控制,使算法研究与硬件实现相结合,缩短了真实系统的开发时间,提高了控制算法的准确性和实用性.     

EFFECTS OF SAMPLE THICKNESS ON BITE FORCE FOR RAW CARROTS AND FISH GELS

The effects of food thickness on human bite force were investigated using a multiple‐point sheet sensor and electromyography. The total force and contact area were directly measured in real time using the sensor, and the average stress detected between the teeth and a food sample (active stress) was derived from the ratio of the force to the contact area. Raw carrots and fish gels with different thicknesses were bitten between the upper and lower incisors or molars by healthy women. For hard and brittle carrots, the peak force, contact area and active stress at the fracture point were greater in thicker samples when biting with incisors. For soft and tough gels, the peak force and contact area were increased as thickness increased; however, the active stress was similar in incisor bites. These values did not differ significantly with thickness in the molar bites of both samples. Although the force and contact area were greater for molar bites than incisor ones, the active stresses at fracture point were independent of tooth position. The sample thicknesses influenced the bite force of humans and the stress applied to the sample, and the effects differed with sample texture.     

A novel estimating method for steering efficiency of the driver with electromyography signals

The existing research of steering efficiency mainly focuses on the mechanism efficiency of steering system, aiming at designing and optimizing the mechanism of steering system. In the development of assist steering system especially the evaluation of its comfort, the steering efficiency of driver physiological output usually are not considered, because this physiological output is difficult to measure or to estimate, and the objective evaluation of steering comfort therefore cannot be conducted with movement efficiency perspective. In order to take a further step to the objective evaluation of steering comfort, an estimating method for the steering efficiency of the driver was developed based on the research of the relationship between the steering force and muscle activity. First, the steering forces in the steering wheel plane and the electromyography （EMG） signals of the primary muscles were measured. These primary muscles are the muscles in shoulder and upper ann which mainly produced the steering torque, and their functions in steering maneuver were identified previously. Next, based on the multiple regressions of the steering force and EMG signals, both the effective steering force and the total force capacity of driver in steering maneuver were calculated. Finally, the steering efficiency of driver was estimated by means of the estimated effective force and the total force capacity, which represented the information of driver physiological output of the primary muscles. This research develops a novel estimating method for driver steering efficiency of driver physiological output, including the estimation of both steering force and the force capacity of primary muscles with EMG signals, and will benefit to evaluate the steering comfort with an objective perspective.     

基于Bayes决策理论的表面肌电信号模式分类的研究

通过对采集的四通道表面肌电信号进行分析,对其建立AR（Autoregressive）参数模型,提取AR模型参数构建特征矢量。根据实际表面肌电（SEMG）信号的随机性特征,提出了一种采用Bayes决策理论对肌电信号的AR模型参数特征进行分类的新方法,并运用最小错误率Bayes分类器,很好地实现了对前臂八种动作表面肌电信号的模式分类。平均识别率为99．125％。此外,还提出采用动态聚类中心的方法对其进行了改进,使其平均识别率提高到99．5％。研究表明,采用Bayes分类器对肌电信号的AR模型参数特征进行分类,是一种有效的处理手段,并可直接应用到其它具有随机性特征的生理电信号的模式分类中。     

基于经验模态分解的牵张反射起始点检测研究

针对痉挛状态患者表面肌电信号易出现虚假的肌电峰值,引起牵张反射起始点前后的信号差异变小,提出经验模态分解去噪与改进样本熵识别的牵张反射起始点检测方法。首先用经验模态分解对肌电信号进行分解;然后以受试者静息状态下的表面肌电信号为参考,设定软阈值对分解的信号进行去噪;最后用改进样本熵识别牵张反射起始点。实验结果表明,经验模态分解算法可以有效地去除肌电信号噪声,而且在改进样本熵的最优参数下牵张反射起始点平均识别率为94%。