This page discusses the sliding-filament model of muscle contraction, where thin and thick filaments slide past each other without shortening. Isometric contractions in isolated muscles like the frog ...This page discusses the sliding-filament model of muscle contraction, where thin and thick filaments slide past each other without shortening. Isometric contractions in isolated muscles like the frog calf show that optimal tension occurs at normal muscle length, with tension decreasing when muscle length changes.