Integration of active pauses and pattern of muscular activity during computer work

Abstract

Submaximal isometric muscle contractions have been reported to increase variability of muscle activation during computer work; however, other types of active contractions may be more beneficial. Our objective was to determine which type of active pause vs. rest is more efficient in changing muscle activity pattern during a computer task. Asymptomatic regular computer users performed a standardised 20-min computer task four times, integrating a different type of pause: sub-maximal isometric contraction, dynamic contraction, postural exercise and rest. Surface electromyographic (SEMG) activity was recorded bilaterally from five neck/shoulder muscles. Root-mean-square decreased with isometric pauses in the cervical paraspinals, upper trapezius and middle trapezius, whereas it increased with rest. Variability in the pattern of muscular activity was not affected by any type of pause. Overall, no detrimental effects on the level of SEMG during active pauses were found suggesting that they could be implemented without a cost on activation level or variability.

Practitioner Summary: We aimed to determine which type of active pause vs. rest is best in changing muscle activity pattern during a computer task. Asymptomatic computer users performed a standardised computer task integrating different types of pauses. Muscle activation decreased with isometric pauses in neck/shoulder muscles, suggesting their implementation during computer work.     

Effects of a thermal-insulating mouse pad on temperature of forearm and hand during computer tasks

This laboratory experiment studied the effects of a thermal-insulating mouse pad on arm temperature and comfort during computer work. Fourteen subjects performed two 20-min computer tasks (a mouse task and a combined task alternating keyboard and mouse use), under three conditions, namely with: 1) a thermal-insulating pad; 2) a placebo pad; 3) no pad (desktop). The temperatures of the forearm, wrist, hand and fingers were measured with four thermocouples. Comfort and discomfort were determined by two visual analogue scales. No arm temperature differences were found between the experimental conditions after performing the combination task in any location. After the mouse task, however, arm temperature decreased significantly less with the thermal-insulating mouse pad than with the placebo pad. The thermal-insulating pad was rated as more comfortable and less uncomfortable than a regular desktop during mouse tasks. A large size is recommended for the thermal-insulating pad.     

Motor-unit recruitment in the trapezius muscle during arm movements and in VDU precision work

It has been hypothesized that shoulder myalgia, which is common in many occupations involving light-to-moderate manual work, is due to an overuse of low threshold muscle fibers, causing damage at the muscle cell level. The present study was undertaken to investigate in the trapezius muscle, (a) to what extent it is possible to track low threshold motor-units in non-isometric conditions, and (b) to study the effect of arm movements on recruitment and firing patterns. Intramuscular four lead fine wire electrodes were inserted in the trapezius muscle of four volunteers, who performed arm movements (shoulder abduction–adduction 0–90–0° in the scapula plane), as well as standardized work using computer mouse. Three channels of electromyography (EMG) were used for motor-unit action potential (MUAP) identification and signal decomposition. Results showed (a) that it was possible to perform signal tracking during slow movements, and (b) that there were motor-units that were active over a wide range of shoulder abduction movement, as well as in work with computer mouse. The findings indicate that stereotypic recruitment patterns exist in the trapezius muscle not only in static work, but also in work situations involving arm and shoulder movements.

Relevance to industry

Occupationally related chronic shoulder pain is an increasing problem in industry, in manual work as well as in computer work. This paper presents results of studies on muscular activity patterns during movements which support the notion that chronic pain may be evoked by overuse syndromes at the muscular fiber level. Practical precautions to reduce such risks are discussed.     

Design of an electronic instrumentation for measuring repetitive hand movements during computer use to help prevent work related upper extremity disorder

Repetitive movements for computer users can result in complaints caused by extreme hand posture, finger movements, and force when using the computer, which is known as Work Related Upper Extremity Disorder (WRUED). This study is about the construction of electronic instrumentation for monitoring and quantifying these movements and forces, using sensors to register wrist posture and fingertip force with software developed to collect and process the data. Tests evaluated the performance of the instrumentation with seventeen subjects participating in this study. The maximum extension observed for the first test was 41°, however after training the subject decreased this value to 33°. Six subjects had a wrist extension of between 15° and 41° for the first test; five reduced their wrist extension (between 3° and 33°) during the second test (p = 0.08) while one subject increased instead of decreased it. No subject performed fingertip force greater than 0.77N during the first test; this was reduced to 0.57N during the second test (p = 0.04). The average typing frequency in the group decreased from 3.2Hz to 2.5Hz during the second test (p = 0.01). Results confirm that this solution may potentially contribute to hand movement reeducation, thereby reducing the risk of WRUED for computer users.

Relevance to industry

Knowledge of repetitive movements during computer use and associated WRUED is essential for prevention. This electronic instrumentation aids the correction of hand movements, which reduces the risk of injury due to inappropriate posture, extreme range of movement, or force during computer use.