There are several exercises in a ballet class which are designed to warm up the smaller muscles of the lower legs and feet, and the frappé is that type of exercise. The frappé begins with the foot in a flexed position near the opposite ankle, and the working foot is quickly and with force, pushed out to a straight position while striking the floor in the process.
In the traditional Russian ballet the foot does not strike the floor and is not flexed but instead is wrapped around the ankle of the supporting leg. This way, the frappé happens when the working foot strikes the standing ankle.
The frappé can also be performed in doubles which is accomplished by alternating beats to the front and the back before the strike.
The purpose of the frappe in the barre section of a ballet class, is to teach muscle coordination with small, quick movements of the feet, build strength and control in the ankles, and warmup the leg muscles for the center exercises yet to come.
The ballet class pianist will be using a 2/4 or quick 4/4 meter with sharp quick accents. The tempo needs to be moderate and controlled and the beat strict. The traditional strong downbeat with a secondary beat on count three works perfectly for this exercise. The trick to inspiring the dancers in the frappé is to choose effective chord progressions and melodic material. A lot of variety within the melodic phrase is effective with strong clear arrivals at the beginnings of each new phrase.
The most support can be given to the dancers by focusing the music on the striking motion and using the same technique on the keyboard. The staccatos need to be sharp and clear. Don’t overemphasize the accents, since the short quick notes have an accented quality already. The dancers are working with medium to small muscles and relatively small motions, so the music should have an understated quality. This will help the dancers to focus and eliminate the danger of distracting them with the music.
For more descriptions of how ballet class music is performed for the various ballet class exercises, read the posts about adage, petit battement and grand battement.