Have you ever wondered why when you become afraid in a dream and you wake up, your heart is still beating fast. The fear was in the dream, it was unreal – then why is the heart beating so fast? Why is it beating fast even after you are awake? The heart is beating fast because it does not know whether the fear was in a dream or whether it was in reality. The heart just knows that there is fear. Just like this, if you imagine that you are exercising it will be as helpful as if you had really exercised; there is no difference that is why the people who were knowledgeable in these things created these techniques. If you put them into a small cell it would not harm their health because they would rest for 15 minutes and do their exercise in this way.
Try this. Who ever is unable to go out can use this technique as well as the meditation for sleep which is to be done at night. You can do them both just before sleeping. The body can be purified in this way. And if the body is pure, this will itself be a great joy, and in this joy you can go deeper inside. This is the first step.
There are two other steps: purification of thought and purification of the soul. On the periphery there are three steps: Body Purification, Mind Purification and Emotional Purification; and then there are three steps for the center: Bodylessness, Thoughtlessness and freedom from emotions. When these six stages are completed, Samadhi happens.