Isometric exercise and Workout

Isometric exercise noun - Muscle-building exercises (or a system of musclebuilding exercises) involving muscular contractions against resistance without movement (the muscles contracts but the length of the muscle does not change).

Workout and isometric exercise are semantically related. In some cases you can use "Workout" instead a noun phrase "Isometric exercise".

Workout noun - Something done over and over in order to develop skill.

Isometric exercise and workout are semantically related. Sometimes you can replace phrase "Isometric exercise" with "Workout", this terms are similar.