A well known technique to relax the body is to squeeze certain parts of the body and then relax it. The differential or rebound effect helps in greatly relaxing the muscles in the body than just merely trying to relax the muscles without causing tension or effort first.

The yogis in the olden days knew that the mind is indeed restless and difficult to control. They knew that the easiest way to get a restless mind to settle down required working with the body. They found out that by twisting the body mindfully into different forms and then letting go, enabled sinking deeper into the body and accessing deeper reaches of the consciousness which otherwise is not very easy to reach.

In verse 6.35, of the Bhagavad Gita, Krishna tells Arjuna that the mind is indeed very difficult to control and it is by practice and dispassion that it can be brought under control

असम्शय महाबाहो मनः धुर्निग्रह अछलम्

अभ्यासेन थु कौन्तेय वैराग्येन च गृह्यते

In fact, the majority of the benefits of yoga are only obtained when one sinks deep into a pose and is able to maintain it with comfort for a while. This aspect of holding a pose comfortably is such a key aspect of asanas that Patanjali in fact devotes one of the three sutras on asanas, in the yoga sutras, to this topic. Patanjali describes an asana as a pose that one can hold steadily with comfort.

स्थिर सुखम् आसनम् (YS 2.46)

That is why, in some yoga traditions like the Iyengar yoga tradition, importance is given to holding a pose in a relaxed manner for a long time, sometimes for fifteen minutes to half an hour, or for even longer, in poses like Shirashasana (Head Stand) and Sarvangasa (Shoulder Stand).

One might ask, "What about vinyasa traditions like Ashtanga Yoga? Are they not useful in sinking deep within ?". The Vinyasa traditions are flow based. It is important to realize that the Ashtanga Vinyasa system was developed for young people in their teens, as a way to dissipate their restless energy and bring their minds to a some semblance of steadiness to prepare for scholarly learning (see section 3 titled "Misunderstanding tapas" in this article). T.Krishnamacharya, the father of modern day yoga, developed the sequence of asanas which we now call the Ashtanga Yoga to teach teenagers in the Mysore palace .

Krishnamacharya teaching students in the Mysore palace in the 1940's

In this tradition, a strong emphasis is laid on the use of the Ujjayi (victory) breath and the bandhas(body locks), along with Dhrishti (focus of gaze) to harness the prana and focus the mind by getting into a flow state (see this article for details). Naturally, with its initial target being teens, it is quite a physically demanding practice. To be able to quickly enter various difficult poses needs a strong flow of prana in the body which needs continuous Ujjayi breathing and the use of bandhas. Many a Ashtanga Vinyasa teacher has, therefore, hurried his or her students when they had spent too long in a pose lest it should induce lethargy and make the body less malleable to do the demanding sequence of asanas. Nevertheless, if they understand the bigger context of yoga and how one needs to take the time to settle into a pose to gain the maximum benefit, they might appreciate the student's intent.

So next time you do yoga, see if you can completely relax in a pose and let go of discomfort in all parts of the body. You will enter a very precious state and the body might give you some answers to questions you may have had. This insight that develops is one of the best gifts Yoga can give you.