There are 16 possible rhythmic variations over 1 beat using quarter notes, eighth notes, sixteenth notes, quarter, eighth and sixteenth note rests and the dot.
Using these 16 rhythms as the basis for practice ideas allows us to develop the technical facility necessary to play countless ideas while practicing small numbers of exercises. For example, using one limb and a sound source, it is possible to play 65,536 different rhythms in * time, by joining the sixteen rhythmic possibilities together in different ways.
If another limb was factored in the equation, the number of possible rhythmic variations would be 4,294,967,296. There are still two or more limbs, countless sound sources, accent possibilities, sticking possibilities etc. The possibilities are infinite.
Two points are important here:
Musical choices are greatly expanded by mastering the ability to improvise with one or more limbs while playing various ostinatos (repetitive patterns). This process is called independence. The ostinatos will vary depending upon the musical style, e.g., playing in a rock style often requires independence with kick or snare while playing a repetitive eighth note hi-hat pattern. The kick and or snare play varied rhythms based upon the bass guitar line primarily and or the chordal and melodic instrument parts.
A useful exercise for developing bass drum independence in the rock style would be; bass drum plays each of the 16 rhythmic variations with the following ostinato.
Here are the remaining 15 rhythmic variations.