Troponin proteins regulate calcium sensitivity in the myofibril contractile apparatus of striated muscles. Troponin I (TnI), along with TnT and TnC, forms the troponin complex in thin muscle filaments. TnI acts as the inhibitory subunit, blocking actin-myosin interactions and mediating muscle relaxation. The TnI subfamily includes three genes: TnI-skeletal-fast-twitch, TnI-skeletal-slow-twitch, and TnI-cardiac. TnI-fast and TnI-slow are expressed in fast-twitch and slow-twitch skeletal muscles, respectively, while TnI-cardiac is specific to cardiac muscle. This gene encodes the TnI-skeletal-slow-twitch protein, expressed in cardiac and skeletal muscles during early development but restricted to slow-twitch fibers in adults. The protein prevents muscle contraction by inhibiting calcium-mediated changes in actin-myosin complexes.