The training of mindfulness of the body can be called the establishment and maintenance of that capability of peace without impulses and emotions. Do not allow the mind to waver and so begin to think about different matters. Tie the mind with the body, for the basis of mind is body, Samadhi and wisdom.
The body is the basis of sense impressions. So we must try and contemplate the nature of happiness and suffering within both our body and mind, whether walking, sitting, lying down, going to the lavatory, in hunger, or in thurst, whatever happens to us.