Horst was the musical director for the Denishawn company (1916-25) before working as musical director and dance composition teacher for Martha Graham's school and dance company (1926-48).
One memorable piece of advice that Horst gave dancers in his lessons in the 1930s, at times delivered in a sarcastic tone: "when in doubt, turn."[1][2][3][4][5] This is a variant of Ted Shawn's famous line "When in doubt, twirl."[6] The Grateful Dead Almanac adopted it as their motto.[7]
Apart from being a personal friend and mentor to Graham, Horst worked and wrote scores for many other choreographers, including:
Horst composed scores for the Denishawn company, including Japanese Spear Dance (1919). He composed several of Graham's early group works: Primitive Mysteries (1931), Celebration (1934), Frontier (1935), and El Penitente (1940). For Anna Sokolow, Horst composed Noah (1935). He also composed several movie scores.
Horst lectured often on "Dance Composition", "Music Composition for Dance", and "Modern Dance and Its Relation to the Other Modern Arts". He wrote and published two books: Pre-classic Dance Forms (1937) and Modern Dance Forms (1960). He founded and edited Dance Observer Journal (1933-64).
"There was no choreography in those days. We didn't even know the word." Dances were just arranged routines. [...] On a later tour, there was a time, according to Agnes de Mille, when Miss Ruth passed by the piano, which was on stage, asking Louis how much longer she had to go. He murmured encouragingly, that it was only once more around the space and to put in a few spins. This may be the source of his later comments in classes in the '30s in New York "When in doubt, turn", although by then it had become a sarcastic and sardonic comment.