| Sumario: | Objectives. Neck and shoulder problems are increasing among workers, particularly during low-level repetitive tasks. Considering the interaction between neck and shoulder muscles during these tasks, studying the sternocleidomastoid muscle (SCM) activity pattern is crucial. This study aimed to investigate SCM activity during a simulated repetitive task involving muscle fatigue and upper limb elevation. Methods. Nineteen females and 20 males aged 18–35 years with body mass index 18.5–28 participated. Exclusions included musculoskeletal problems within the past 7 days, circulatory/rheumatic/inflammatory disorders, routine engagement in overhead sports or expertise in repetitive movements. Surface electromyography was used to record SCM activity, normalized using maximum voluntary contractions and converted into the root mean square (rms) and median frequency (MF). Pre-fatigue and post-fatigue periods were the first and last 30 s of the task. The craniocervical flexion test assessed deep cervical flexors and their interaction with SCM activity. Results. The rms of SCMs increased bilaterally post fatigue, regardless of sex. Females showed lower MF values in the SCM left side than males, independent of task duration. Conclusion. There were no gender differences. However, SCM changes during upper limb fatigue may indicate overuse of neck muscles during repetitive tasks involving fatigue and upper limb elevation.
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