Measures of localized spinal muscle fatigue

The objective of this study was to determine the best variable, if any, to indicate the level of localized muscle fatigue. Six male and six female subjects were studied while they exerted their maximal voluntary contraction and 40% of maximal voluntary contraction of spinal extensors in an isometric lifting activity. The electromyography (EMG) of erectores spinae at thoracic and lumbar levels was measured bilaterally. Also, the muscle bed blood volume, level of blood oxygenation to erector spinae at L3 level and heart rate were measured. The initial and final values of subjective feelings of fatigue through visual analogue score, rate of perceived exertions and body part discomfort rating were recorded. The mean maximal voluntary contraction forces for males and females were 899 (238) N and 431 (135) N respectively. The mean durations of hold in maximal voluntary fatiguing contraction were 68.1 (39.9) s and 72.3 (37.0) s for men and women respectively. By the end of the hold the force declined to 52% for males and 62% for females. The EMG amplitudes and median frequencies also progressively declined (p < 0.01). ANOVA revealed that the task percentile values of all variables were significantly different (p < 0.01). Gender had a significant main effect (p < 0.01). The correlation coefficients between force and other individual variables were weak to modest, but significant (p < 0.001). None of the single variables predicted fatigue reliably for either gender and levels of contraction. The regression equations developed were highly significant (p < 0.01) and they explained 96 to 98% of variance in both genders and contractions.     

Effects of changes in sitting work posture on static neck and shoulder muscle activity

Abstract

In order to analyse the effect of changing the sitting posture on the level of neck and shoulder muscular activity, an electromyographic (EMG) study of ten healthy experienced female workers from an electronics plant was undertaken. A standardized, simulated task was performed in eight different sitting work postures. Using surface electrodes, the level of muscular activity was recorded as normalized, full-wave rectified low-pass filtered EMG. The results showed that the whole spine flexed sitting posture gave higher levels of static activity in several neck and shoulder muscles than the posture with a straight and vertical spine, which in turn gave higher levels than the posture with slightly backward-inclined thoraco-lumbar spine.     

Review of: “ Systems Documentation: Techniques of persuasion in large organizations”. By FRANK WHITEHOHSE, ( London: Business Books, 1973.) [Pp. viii + 191.] £450.

The use of back belts in industry has increased despite the lack of scientific evidence supporting their efficacy. The purpose of this study was to investigate the effect of a semi-rigid lumbosacral orthosis (SRLSO) on oxygen consumption during 6-min submaximal repetitive lifting bouts of 10 kg at a lifting frequency of 20 repetitions min^-1. Fifteen healthy subjects (13 men, two women) participated in this study. Each subject performed squat and stoop lifting with and without an SRLSO for a total of four lifting bouts. Lifting bouts were performed in random order. Oxygen consumption during the final minute of each lifting bout was used for analysis. A two-way analysis of variance with repeated measures was used to analyse the effects of lift and belt conditions. The stoop and squat methods were significantly different, with the squat lift requiring 23% more oxygen on average than the stoop lift for equal bouts of work. No significant difference was found between the belt and no belt condition within the same lifting technique and no interaction was present. These data suggest that an SRLSO does not passively assist the paravertebral muscles (PVM) in stabilizing the spine during submaximal lifting bouts.     

On Educational Ergonomics

Abstract

This paper represents an effort to establish an inter-disciplinary field of research toward total educational effectiveness. The traditional educational delivery lacks any systems perspective and precision. The application of ergonomics to education has received only limited attention. A systems analysis has identified 5 components for educational ergonomics: (1) learning ergonomics, (2) instructional ergonomics, (3) orgonomics of educational facilities, (4) ergonomics of educational oqutpment, and (5) the ergonomics of educational environment.

Learning ergonomics explores such areas as educational skills of handwriting, roading, drawing, instrument manipulation, class scheduling and school scheduling, research in examinations, management of learning activities, and grading systems. The instructional ergonomics covers textbook design, teaching devices, instruction techniques, classroom conducts, lecture preparation, and educational T.V. Ergonomics of educational facilities concerns educational furniture, laboratory and library ergonomics, classroom and office design, and equipment allocation. Ergonomics of education equipment investigates needs analysis, C/D design, allocation of equipment, performance analyses, and its safety and construction. Ergonomics of educational environment includes such things as illumination, colour, noise, space utilization, and allocation of equipment. Within each variable, research is reviewed and typical studies are suggested. The value of an integrated discipline of educational ergonomics is also discussed.     

Effects of heel cushioning elements in safety shoes on muscle–physiological parameters

Safety shoe designs are primarily based on safety requirements. But all-day comfort should not be luxury: Heel strike associated impact loads on joints need to be compensated by active muscular effort and safety shoes should support this protective function of muscle activation. In 10 healthy men, 12 trunk and leg muscles were analyzed with surface electromyography. Subjects walked on a walkway while wearing different safety shoes with the test shoes being equipped with exchangeable cushioning heel inserts according to individuals' body weight. While wearing the optimally cushioned shoes the cumulative muscle activity per distance travelled dropped clearly compared to the regular safety shoes, demonstrating reduced muscular effort. Also, the heel strike associated amplitude peak of back muscles occurred earlier within the stride while wearing the test shoes. Thus weight-balanced cushioning heel inserts in safety shoes proved able to reduce muscle strain, logically delaying muscular fatigue and extending muscular joint protection.Relevance to industryAdjustable heel inserts in safety shoes are suited to improve the health status of employees by reducing muscular effort so that active joint protection can be prolonged.     

Functional changes in cerebral and paraspinal muscle physiology of healthy women during exposure to whole-body vibration

The objective of this study was to investigate the effects of whole-body vibration on multiple tissues simultaneously in fourteen healthy women. On three separate days, participants were exposed to frequencies, 3, 4.5, or 6 Hz (at 0.9 g_r.m.s acceleration in vertical direction) per day on a simulator for 16 min. While sitting ‘with’ and ‘without’ backrest support, participants also performed handgrip contractions for 1 min. Cerebral and lumbar muscle oxygenation and blood volume responses were measured using near-infrared spectroscopy. Cardiorespiratory responses were collected using a metabolic cart. In general, cerebral and cardiorespiratory responses increased with vibration compared to without vibration, whereas in the lumbar region oxygenation and blood volume responses decreased. Greatest cerebral responses were observed at 6 Hz (P < 0.05). When compared to exposure to vibration without performing work, significant decrease in lumbar responses was observed during handgrip contractions in both conditions of sitting ‘with’ and ‘without’ a backrest (P < 0.05). Such decreases in the lumbar responses suggest postural load due to prolonged sitting combined with physical activity during vibration, might reduce vascular supply to the paraspinal muscles. This study reiterates the importance of understanding the physiological basis for various health disorders in women due to exposure to whole-body vibration.     

Morphological investigation of low back erector spinae muscle: Historical data populations

Accurate and reliable low back morphological data such as the cross-sectional area (CSA) of the erector spinae muscle (ESM) is vital for biomechanical modeling of the lumbar spine to estimate spinal loading and enhance the understanding of injury mechanisms. The objective of the present study is to enhance the current database regarding ESM sizes by studying with larger sample sizes, collecting data from live subjects, using high resolution MRI scans, using computerized, reliable, and repeatable measurement techniques, and analyzing data from three inter-vertebral disc (IVD) levels for both genders. A total of 163 subjects (82 males and 81 females) were included in the study. CSAs of both right and left ESMs were measured from axial-oblique MRI scans using architectural design software. The average CSA of the ESM was 23.50, 24.22, and 24.33 cm² for females and 30.00, 28.28, and 24.60 cm² for males at the L3/L4, L4/L5, and L5/S1 levels, respectively. Results agree with some studies, but generally larger than most previous studies, possibly due to differences in sampling (sample size, subject characteristics: age, anthropometrics, cadavers, etc.), measurement techniques (scanning technology, scanning plane, scanning posture, different IVD levels), or muscle definitions.Relevance to industryLifting tasks are very common in occupational settings and associated with low back pain. Accurate and reliable low back muscle size data is of importance to produce more efficient low back biomechanical models to better understand the loading mechanism in lifting tasks and to minimize low back pain risk regarding the lifting task. However, available low back muscle size data are quite limited. This study fills part of this gap by providing data from a large sample population of live subjects, multiple levels, both genders, high resolution MRI scans, reliable and repeatable measurement technique. The updated low back muscle size data presented in this paper can be used by biomechanical modelers to improve current low back biomechanical models.     

盾构管片拼装机用行星齿轮减速器的研制

用于大直径（大于11m）隧道盾构管片拼装机上的行星齿轮减速器原是从日本EATON公司引进，经本公司在上海4条过江隧道使用后，其主要传动件均已磨损，其中驱动用油马达和液压制动器的摩擦片等均为日本标准，维修更换困难，供货周期与价格均不理想。根据作者多年的工作经验和国内现有制造条件，该减速器自行研制是可行的。     

腰部运动损伤防护智能服装的研发

针对硬拉项目初学者易出现腰部肌肉损伤的问题,研发了穿戴肌肉疲劳度检测系统,使穿戴者实时掌握竖脊肌疲劳度情况,从而避免肌肉过度疲劳。系统以可穿戴Myoware肌电传感器与Arduino UNO开发板为基础,完成对表面肌电脉冲信号的采集和计算,并将计算得到的表面肌电平均功率频率与肌电疲劳阈进行比较,判定是否达到肌肉疲劳。通过测量4名男性大学生硬拉运动过程中肌肉电信号从开始到疲劳恢复过程中的变化数据,将150 Hz作为该目标群体的肌电疲劳阈。同时,考虑各电子模块的可穿戴性和运动紧身衣的可洗涤性,以可拆卸式风琴袋作为载体,实现电子模块与运动紧身衣的结合。