An isotonic lift is when the weight or load is constant, but the speed throughout the lift varies due to the fact that we are human. This describes almost every lift that has a set resistance throughout the range of motion. This is the opposite of an isokinetic exercise that has a variable resistance throughout the movement, but has a set speed. Any exercise with free weights, and most machines in fitness gyms are isotonic. The figure above shows a man doing an olympic lift called the snatch, which is isotonic. The barbell has a set amount of weight on each end that stays the same throughout the lift. Since he is not a robot he will inevitably lift with variable speed throughout the range of motion.