His strength was demonstrated by his swinging the axe in The Magnificent Seven or digging the tunnel in The Great Escape or his boxing skill in Hard Times.
Among his other movies, The Mechanic, Mr. Majestyk, St. Ives, The Stone Killer, Death Wish and its many sequels.
And he did his own stunts... As noted by the this scene in Breakheart Pass. The train was going about 45 miles per hour at the time this scene was made.