Isotonic contractions are distinctly different from isometric contractions, in that they occur with movement at the joint.
Other types of isotonic exercise include body weight strength training, such as pushups or pull ups, weight machines like Bowflex and Nautilus, and the use of resistance bands.
Many people pay careful attention to the positive phase of isotonic type exercise, but ignore the negative phase and allow gravity to assist them as they lower the weight.
When someone says that they are performing isotonic exercise, it means that they are performing an exercise that involves muscle contraction against a constant load.
While there are many positive things about eccentric isotonic exercise, it's only fair to mention that some experts believe that it may be a cause of injury.
For example, during physical therapy, you might not be strong enough for isotonic movement so isometric contractions might have to work.
There are two different types of isotonic exercises and you need to learn both to understand the answer to "what is isotonic exercise?"
Both phases -- flexion and extension -- are equally important as you move the weight through the range of motion in isotonic exercise.
Isotonic exercise engages the muscles by flexing and extending them through a range of motion against a fixed level of resistance.
The phase where you lift the weight is often referred to as the positive phase of the isotonic exercise, while the part where you lower the weight is called the negative phase.