Muscle endurance refers to an indiviual's capacity to repeate or sustain muscular contraction for a prolonged period of time.  As general rule, exercise sessions that involve exercise of a lesser intensity, which therefore permit a great number of repetitions, stimulate adaptations that are in accordance to the development of  muscular endurance and muscle tone.

For muscle endurance/toning exercise, the number of repetitions needs to be quite high.  Each exercise should be performed between approximately 12 and 15 times, although as many as 25 can be performed if your client wants to build up endurance.  The repetitions should be performed smoothy, and with good technique.  Technique should not be lost for the sake of speed.