We perform Isotonic exercise or movements daily.
Isotonic exercise is a type of exercise or movement where the resistance is fixed (stays the same) but the speed of the movement differs throughout the range of motion.
This is the exact opposite of Isokinetic exercise.
Normal gym machines or just lifting weights makes use of Isotonic exercise, with examples such as leg curl machines, bench press and even sit ups.
Say you choose to press 10 kilogram dumbbells overhead, the weight (or resistance) stays the same throughout the whole range of motion, but you can decide to do it fast or slow (changing the speed).
Unlike Isometric exercise, during Isotonic exercise the muscle lengthens and shortens and there is a change in the angle of the joint.