Effect of Manganese Exposure on Multi-Finger Coordination with Asymptomatic Welder

Chronic exposure to manganese in occupational settings such as welding is known to accumulate in the basal ganglia and disrupt motor control. Although clinical symptoms emerge only after considerable neural damage, subtle motor deficits may exist in asymptomatic individuals. This study aimed to identify such subclinical motor alterations by examining multi-finger coordination in professional welders. Nine professional welders with more than 20 years of welding experience and ten age-matched healthy controls participated in the study. Participants performed three isometric finger force tasks: a maximal voluntary contraction task to assess maximal finger forces, a single-finger ramp task to evaluate finger enslaving, and a multi-finger quick pulse task to analyze motor synergies and anticipatory synergy adjustments (ASA). Surface electromyogram was recorded to quantify muscle co-contraction. Compared to controls, welders exhibited reduced motor synergy strength, delayed and decreased ASA, and increased antagonist muscle co-contraction. These findings suggest that long-term occupational welding exposure, which involves manganese as a major component, is associated with subtle but measurable alterations in motor coordination and neural control strategies, even in the absence of clinical symptoms. Multi-finger synergy analysis and co-contraction metrics may serve as sensitive markers for detecting early motor dysfunction in populations occupationally exposed to neurotoxic substances.