Shoulder strain in keyboard workers and its alleviation by arm supports

Summary Keyboard work consists mostly of dynamic contractions of the small muscles of the forearms and hands. This is accompanied by continuous activity in the arm, shoulder and neck muscles keeping the head and hand in the correct position. Eliminating the weight from the arm by means of support and the position of the arms influences the electrical activity of shoulder muscles when working at a keyboard. We studied the influence of elbow angle, as well as that of different arm supports, on electrical activity of upper trapezius muscle during keyboard work in healthy workers and persons suffering from shoulder pains. The measurements were carried out in the laboratory. EMG activities, which where measured as mean square root (RMS)-values at every 100-millisecond period in trapezius muscle when working, were lower, the greater the elbow angle. Furthermore electrical activity decreased when subjects used arm supports while working. It is evident that the static load to shoulder muscles can be lowered significantly in keyboard work, when the forearms are at an angle of at least 100 degrees and by using arm supports. The most convienient and ergonomic working position can also be found individually be the method used here.     

On the role of static and dynamic visual afferent information in goal-directed aiming movements

Movement planning has been shown to be optimized when the participant is permitted to see his or her hand resting on the starting base prior to movement initiation. However, this proposition is opposed by contradictory results. In the present study, we wanted to determine whether these conflicting results were caused by procedural differences. The results showed that seeing one's hand on the starting base did not result in more accurate aiming movement than when this information was not available. However, lower aiming errors were found when one was asked to foveate the starting base and then the target prior to movement initiation, but only when no dynamic visual information was available during movement. When an aiming movement was performed while one's hand was visible in visual periphery, foveating the starting base or not prior to movement initiation did not modify aiming accuracy. These results suggest that gazing at the starting base and then at the target provides an eye-based representation of the movement to be performed that can be used by the CNS to plan a manual aiming movement. Information for better planning of the direction – but not the extent – dimension of an upcoming movement can also be derived from dynamic visual information available in peripheral vision. Electronic Publication     

Physiological effects of dynamic work on a bicycle ergometer combined with different types of static contraction

Summary The effects on heart rate, oxygen uptake, and pulmonary ventilation of muscular exercises, including both dynamic contractions, either simple or combined, were studied in 4 male subjects, aged 21 to 23 years. The dynamic work consisted in cycling on an ergometric bicycle at three power levels: 40, 80, and 100 W. The static work consisted in pushing against, pulling and holding with the arms a 6, 9, 12, or 18 kg load. The physiological effects are expressed as cardiac cost (HR), oxygen cost (VO₂) and ventilation cost (V). The physiological cost of the combined work increases according to the cycling power and to the isometric load developed. A statistical analysis shows that the costs of combined work are not different from the sum of the costs of the static and dynamic contractions measured separately. Thus, the physiological responses to the combinations investigated are of an additive type.     

磁场对微循环的影响

为了探讨磁场对微循环的作用，利用直径０．７ｃｍ、表面磁感强度０．３Ｔ的磁片及磁感强度０．１Ｔ、转速２５００ｒ／ｍｉｎ的旋磁机分别作用于受试者左手无名指３０ｍｉｎ，并记录作用前后微循环改变。结果表明，动、静磁场均可使微血管清晰度、血流速及管径有明显改变，而对管袢数与红细胞聚集没有影响。这一结果提示，微血管扩张、血流速加快是磁场改善微循环的基础。     

Microcirculation in the upper trapezius muscle during varying levels of static contraction,fatigue and recovery in healthy women —a study using percutaneous laser-Doppler flowmetry and surface electromyography

Summary Microcirculation in the upper portion of the trapezius muscle was measured percutaneously by continuous laser-Doppler flowmetry (LDF) during two 10-min series of alternating 1-min periods of static contraction and rest determined electromyographically (EMG). Stepwise increased contraction was induced by keeping the arms straight and elevated at 30, 60, 90 and 135°, which was repeated with a 1-kg load carried in each hand. Thereafter, fatigue and recovery were recorded while the subject kept her arms straight and elevated at 45° carrying the 1-kg hand load as long as possible, followed by rest with arms hanging and no load. A group of 16 healthy women of different ages was studied. Signal processing was done on line using a 386 SX computer. The LDF- and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) and median spectrum frequency were performed. The rms-EMG increased significantly with an increase in the calculated shoulder torque (r=0.75). Accumulated local fatigue was indicated by a decrease in MPF with increased shoulder angle and added load (r = –0.54). Blood flow increased with increased shoulder angle (r=0.82, with hand loadr=0.62) and with increased shoulder torque (r=0.72), and also showed a significant increase with increased EMG activity (r=0.74). The LDF showed a negative correlation to MPF (r= –0.67), with increased values when MPF was lowered. During the endurance test, a moderate increase of LDF occurred which reached its maximum during the 1st min of recovery. Then, a slow return to the base level was recorded. The ability to increase the flow in the microcirculation with increasing muscle load was not diminished with age.     

Comparison of static and dynamic models of maternal immunization to prevent infant pertussis in Brazil

BackgroundThis paper compares cost-effectiveness results from two models of maternal immunization to prevent pertussis in infants in Brazil, one static, one dynamic, to explore when static models are adequate for public health decisions and when the extra effort required by dynamic models is worthwhile.MethodsWe defined two scenarios to explore key differences between static and dynamic models, herd immunity and time horizon. Scenario 1 evaluates the incremental cost/DALY of maternal acellular pertussis (aP) immunization as routine infant vaccination coverage ranges from low/moderate up to, and above, the threshold at which herd immunity begins to eliminate pertussis. Scenario 2 compares cost-effectiveness estimates over the models’ different time horizons. Maternal vaccine prices of $9.55/dose (base case) and $1/dose were evaluated.ResultsThe dynamic model shows that maternal immunization could be cost-saving as well as life-saving at low levels of infant vaccination coverage. When infant coverage reaches the threshold range (90–95%), it is expensive: the dynamic model estimates that maternal immunization costs $2 million/DALY at infant coverage > 95% and maternal vaccine price of $9.55/dose; at $1/dose, cost/DALY is $200,000. By contrast, the static model estimates costs/DALY only modestly higher at high than at low infant coverage. When the models’ estimates over their different time horizons are compared at infant coverage < 90–95%, their projections fall in the same range.ConclusionsStatic models may serve to explore an intervention’s cost-effectiveness against infectious disease: the direction and principal drivers of change were the same in both models. When, however, an intervention too small to have significant herd immunity effects itself, such as maternal aP immunization, takes place against a background of vaccination in the rest of the population, a dynamic model is crucial to accurate estimates of cost-effectiveness. This finding is particularly important in the context of widely varying routine infant vaccination rates globally.Clinical Trial registryClinical Trial registry name and registration number: Not applicable.     

Forces and moments on the human leg in the frontal plane during static bipedal stance.

An experimental apparatus was assembled that permitted measurement of the vertical and lateral ground reaction forces as the hip is abducted, resulting in foot separations ranging from 0.25 to 71 cm, with the knee in 0 degree flexion. Twelve healthy volunteers (8 men and 4 women) were tested. The hip joint was located by means of center of rotation measurements on each subject's legs, and the location of the knee joint was determined using anatomical measurements. It was observed that the mediolateral force was nonzero and directed toward the body midline, even when the subject's feet were placed together. With the feet placed at shoulder width, the population mean mediolateral force was 3% of body weight. It was determined that simplifying assumptions based upon either "zero lateral force," or "zero hip moment," produced errors, when compared with our measured values, over various ranges of foot separation, with the zero hip moment assumption providing accuracy over a broader range. The inclination of the tibial plateau, with respect to the long axis of the tibia, that would produce minimal mediolateral shear at the knee is presented. Research and clinical applications of our results and techniques are discussed.     

人体静态眼球反旋转反应的初步观察

目的观察人体于不同的头位倾斜条件下诱发的OCR反应特征,为建立其检测方法和实际应用提供依据.方法受试对象为地面人员22名和飞行人员11名,端坐于装有特制头托的座椅上,通过头位在冠状面内分别处于左右各倾斜30°、50°、70°的位置诱发静态OCR反应.采用红外视频眼动记录方法分别随机测定从头直位到左右各30°、50°、70°的眼动视频信号.最后以动头前即刻的眼球位置为零位,以眼球虹膜纹理为标志,对各时刻虹膜纹理与初始状态虹膜纹理进行互相关分析,找出相关度最大的一点为各时刻眼球位置,测量该时刻眼球与初始眼球位置的角度即为眼球扭转角度.结果头位倾斜引起的典型OCR反应曲线特征是,头位倾斜动作开始,首先引起一个幅度较大的与头动方向相反的眼球反方向旋转,随之,眼球反转角度逐渐减小,在头位倾斜到固定角度后,眼球反转角度在一定范围内波动或不变,未发现头位向同一方向倾斜不同角度引起的OCR有显著差异.飞行员与正常地面人群OCR反应未见显著差别.结论静态头位倾斜可以诱发出OCR反应,可用来评价耳石器功能.