Evidence for repetitive load in the trapezius muscle during a tapping task.

Many studies describe the trapezius muscle activation pattern during repetitive key-tapping focusing on continuous activation. The objectives of this study were to determine whether the upper trapezius is phasically active during supported key tapping, whether this activity is cross-correlated with forearm muscle activity, and whether trapezius activity depends on key characteristic. Thirteen subjects (29.7 ± 11.4 years) were tested. Surface EMG of the finger's extensor and flexor and of the trapezius muscles, as well as the key on-off signal was recorded while the subject performed a 2-min session of key tapping at 4 Hz. The linear envelopes obtained were cut into single tapping cycles extending from one onset to the next onset signal and subsequently time-normalized. Effect size between mean range and maximal standard deviation was calculated to determine as to whether a burst of trapezius muscle activation was present. Cross-correlation was used to determine the time-lag of the activity bursts between forearm and trapezius muscles. For each person the mean and standard deviation of the cross-correlations coefficient between forearm muscles and trapezius were determined. Results showed a burst of activation in the trapezius muscle during most of the tapping cycles. The calculated effect size was ≥0.5 in 67% of the cases. Cross-correlation factors between forearm and trapezius muscle activity were between 0.75 and 0.98 for both extensor and flexor muscles. The cross-correlated phasic trapezius activity did not depend on key characteristics. Trapezius muscle was dynamically active during key tapping; its activity was clearly correlated with forearm muscles' activity.

Work and workload of nursing personnel in a nursery school and two institutions for handicapped children.

Work-related low back pain and cervicobrachial disorders have become increasingly common among nursing personnel with the increase in the number of social welfare institutions and workers. The aim of this study is to assess the burden on the low backs of personnel caring for children. We measured work content, working time, posture and muscular activity in 16 nursery workers in three different types of institutions for healthy and handicapped children. The working time and posture of 7 nursery teachers in a public nursery school for healthy children (A school), 7 nursing workers (4 nursery teachers and 3 nursery instructors) in a public daycare center for mentally and physically handicapped children (B center), and 2 nursery instructors in a private home for severely handicapped children (C home) were analyzed. The muscular activity of the erectores spinae muscle of three subjects was measured using a newly developed EMG monitor (portable EMG monitor, PEMM). The following results were obtained. The average length of a lesson or activity in A school was greater than that in B center and C home. The time required by care for meals was longest in C home. The arrangement and rearrangement times were longest in the classes of children aged 3-5 in A school. The time occupied for clerical work and other work was relatively longer, while recess including lunch time was approximately one hour. The most commonly observed posture was sitting on the floor in all kinds of classes, with this occurring most often in C home. Hazardous postures such as bending forward, squatting, and kneeling appeared in 11-18% (48-81 min) of a day's working time. The average muscular activity of the erectores spinae muscle of three subjects throughout a day was approximately 10% of the maximum isometric contraction (% maximum work load, %MWL), when muscular activities were measured by PEMM. The relatively high %MWL values (19-27%MWL) were obtained at a slightly bending posture and a kneeling posture, while lower (1-9%MWL) values were observed at a sitting posture. The %MWL values at a sitting posture varied according to such conditions as duration of sitting, back rest, weight on the arms, twisting of the trunk, and hip movement. The risky nature of the sitting posture are also discussed.

[Cervicobrachial occupational diseases in office workers]. / Arbeitsbedingte cervicobrachiale Beschwerden bei Büroarbeiten.

A comparison of Japanese and Swiss studies on keyboard operators in office work shows that objective and subjective symptoms of injuries in muscles and tendons of te cervicobrachial region are frequent in both countries. It is possible to demonstrate a clear relation between workplace dimensions, postures and impairments. We agree with the Japanese view, that the localised symptoms should be considered as a syndrome of Occupational Cervicobrachial Disorder.

[Ergonomic design of alpha numeric keyboards]. / Ergonomische Gestaltung von alphanumerischen Tastaturen.

Split keyboards have been developed based on laboratory and field studies. They are characterized by a large forearm/hand support, an angle between the two half keyboards of 25 degrees, a frontal-, lateral inclination of 10 degrees and a hand-conforme key arrangement. These split keyboards reduce constrained postures in arms and hands. The keyboard can be operated with supported forearms. Work on a split keyboard is more comfortable and it was preferred by a large majority of the users.

[Comparison of muscular load between normal handwriting and constrained writing forced by optical character reader (OCR) cards].

Optical character readers (OCR) were introduced into an office as input devices for a computer system. In order to input data in to the system, workers of this office had to write down the data on sheets of specially formatted paper, called OCR cards. Some workers engaged in this task complained of symptoms of occupational cervicobrachial disorders (OCD). Observation suggested that the constrained motion of writing on OCR cards may cause such symptoms. Therefore, in order to prevent OCD, the writing motion was analyzed. The electromyogram of the upper extremities and shoulders was also compared between normal handwriting and constrained writing on the OCR cards in laboratory studies. The results were as follows. 1. Writing time per letter for the OCR cards was longer than that for normal handwriting. 2. Discharge of muscles observed through electromyogram was larger per letter for the OCR cards than for the normal handwriting. 3. Discharge from the trapezius per unit time for the OCR cards was rather large. This phenomenon showed that the workload of constrained writing was heavier than that of normal handwriting. The results suggests that more careful preventive measures for OCD should be promoted in comparison with ordinary clerical tasks.

Hand differences on a sensory test using tactual stimuli.

To examine hand differences in the sensory feeling of texture, 35 subjects made sensory evaluations with the left and the right hands to a tactile stimulus (sponge rubber) and also marked on a 5-point Likert scale 50 adjectives which represented various tactual feelings. Factor analyses, applied to the data of 35 subjects, showed that the left hand related more to a keen and sharp dimension while the right hand related more to a mild and soft dimension of the tactile stimulus. Possible relations of these hand differences in sensitivity to hemisphere functioning were discussed.