The sutra that refers to these terms is sutra 2.46 - The Yoga Sutras of Patanjali
This sentence can be roughly translated as “postures should be stable and comfortable”, and it is also often reworded as the balance between “effort” and “ease.”
Sthira refers to stability, intent, and strength. Etymologically it arises from the root -stha-, which means “to stand, to be firm”.
Sukha refers to comfort, ease, and openness, and the literal meaning is “good space,” from the root words -su- (good) and -kha- (space).
Sthira is the fire; the part of the practice that requires you to be fully present when you enter experiences of discomfort, whether it emerges from the physical body, the mind, or the energetic body. Finding stability in the body and the mind while practising asana, meditation, or any other yogic practice is what can ultimately bring us to balance. “Asana Sthiti”, the steadfastness in the posture. You’ll know you’re experiencing Asana Sthiti when the shape is steady, your muscles are engaged and your breath is rhythmic and supportive of the moment unfolding before you. Your mind will be present and observant.
Sukha occurs when we learn to let go. It’s the part of the practice where, as we become more and more familiar with ourselves, we begin to relax and become more present in the experience without the need to do more or try harder; the law of minimum effort manifests. It is that part of ourselves that truly knows when we’ve “arrived” in the posture. Everything feels aligned and there is no strain in the muscles. The mind feels calm, content and spacious, and prana, the life force energy, can flow freely through us.
On our mat and in our lives we’re constantly in search of harmony between both strength and stability, as well as flexibility and freedom. Having too much of one and too little of the other creates imbalance.
