What symptom is indicative of repeated use of the index finger in an assembly line job?

The symptom indicative of repeated use of the index finger in an assembly line job is finger jerking. This condition often arises from continuous and repetitive motion of the finger, which places stress on the muscles and tendons, leading to involuntary movements such as jerking. This can be a result of muscle fatigue or strain, where the finger struggles to maintain control after prolonged use, reflecting the impact of ergonomic stressors in a workplace setting.

In contrast, tinnitus is associated with hearing issues and is not related to finger movement, while full-body fatigue typically stems from overall physical exertion rather than localized repetitive activity. Joint stiffness may occur but is more general and can affect any joint without specifically indicating the repetitive use of the index finger. Thus, finger jerking directly correlates to the specified repetitive task, making it the most relevant symptom in this context.