Troponin I is the inhibitory subunit of troponin, the thin filament regulatory complex which confers calcium-sensitivity to muscle actomyosin ATPase activity. Expressed in body-wall musculature, with weak expression in late-stage embryos and strong expression during the larval and adult stages. Also expressed in vulval and anal muscles, and weakly expressed in pharyngeal muscle. Worms exhibit abnormal locomotion, unregulated contraction of the sarcomeres due to small portions of each myofibril shortening irregularly and independently from another causing rigid paralysis. This is due to poorly defined sarcomeric structure, with small islands of thin filaments interspersed within the overlap region of A bands and the H zone. Belongs to the troponin I family.