Serious practitioner of Pranayam withhold the breath inside and outside. These are called Antarik and Bahi kumbhak. During Kumbhak the Sadhak is required to concentrate from one chakr to another. This is nothing but practice of Dharna. Dharna is a state preceding Meditation.
To concentrate on one point of the body is Dharna. In the final position of Asan, when the Sadhak is established in practice, he is called upon to concentrate on the required Chakr (Five situated in the spine and above). While doing so he is practicing Dharna at that moment.