[An experimental study on muscle tension reaction induced by voice among sign language interpreters]

The purpose of this study is to ascertain the incidence of cervicobrachial muscle tension induced by voice among sign language interpreters (SLIs). The analyzed subjects included 8 professional SLIs (Case group) who complained of pain in the cervicobrachial muscle when listening to others' talking and 8 other people who have not learned sign language (Control group). Matching sexes, ages, and smoking habits of the Case and the Control groups was carried out. Informed consent to participate in the study was obtained from all subjects. While subjects relaxed in a sitting position, surface electromyographies (EMGs) were recorded from the right and left trapezius muscles and biceps brachii muscles. During this time, all subjects had two listening tasks: to listen to lectures in Japanese and to listen to instrumental music. An inquiry about subjective symptoms was conducted just after each task. Root-mean-square (RMS) values per 100 ms in each of the tasks were calculated for analysis of surface EMG. An original criterion of judgment was that the threshold of RMS values was 3.8 microV, and its threshold continued for more than 1 s. The criterion was used and the muscle tension was confirmed. Results showed muscle tension in the trapezius muscles or the biceps brachii muscles among 5 of 8 subjects in the Case group, and in 1 of 8 in the Control group when listening to the lecture. 3 subjects in the Case group and none in the Control group showed muscle tension in the trapezius muscles when listening not to music but to the lecture. The differences between the Case and Control groups in these results were not statistically significant. Confirmed muscle tension in SLIs when listening to a Japanese lecture is probably induced by the Japanese voice. It is necessary to further investigate whether muscle tension is an acquired reaction from sign language interpreting or a pathological reaction. Listening to Japanese voices may contribute to muscular overload in SLIs so that it may be necessary for SLIs to relax their muscles during break times with an absence of Japanese voices.