Many jazz musicians found the "coll school" limiting and lacking emotion. During the mid-1950s a growing number of young disciples of the bebop style began to from groups that featured improvisation and a increased emphasis on composition within a jazz cortex. These groups were to also feature the drummer as a soloist, often improvisation as an introduction or over the entire form of the tune rather than in an "open solo" style. Max Roach, a notable bandleader in the hard-bop style, was a major exponent of these techniques, as was Art Blakey, a young bandleader whose Jazz Messagers included some of this music's greatest stars early in their careers. Blakey typified the haed-bop style with a forceful backbeat on the hi-hat, as well as the energetic and liberal use of polyrhythm and independence