Andrew Huxley and Niedergerke are the scientists that discovered the sliding filament theory.
They said that the muscle filaments are made up of proteins like actin and myosin. Actin is the thinner protein that is formed of two subunits – G actin and the F actin. They together form the actin filament.
Myosin filament is formed of the units Heavy meromyosin and light meromyosin. These together make the myosin filament. These filaments slide over each other and attach themselves to make the muscle contract.