Let’s look at a couple of terms that can help us understand yogasana.

Yoga has a reputation for stretching, and many people come to yoga seeking more flexibility . Think of the hamstrings: everyone’s got an idea that these need to be more flexible. And, many yoga people will want to devise the most effective stretch to make this happen.

This isn’t incorrect, but it is limited in the scope of what our tissues need, and what they can do, to maintain health (and so you know, my definition of health includes having as many options in movement that you’d like and works in your body).

Range of motion is the amount of movement at a specific joint. It’s not the job of a yoga teacher to measure or assess this, but these ranges are measurable (go see a physical therapist!).

Passive range of motion is the amount of movement at a joint created by an external force. The muscle that creates the movement does not contribute. For example, to move through passive range of motion in the hamstring, you could do supta padangusthasana A (hand to big toe pose, reclining with a strap around the foot and raising the leg). You are using a strap within the hand to move the leg into flexion, the hip flexors are not (or very minimally) engaged in order to create the range. Or, a helper could raise your leg for you.

Active range of motion is the movement created by the muscles that cross the joint. In the example of supta padangusthasana, an active range of motion would be to recline, and to not use the hand or strap, and to raise the leg to a flexed position. This range is created by the hip flexors.

Both types of range are useful to maintaining mobility of a joint and connective tissue. However, passive range of motion will not contribute to strength building, and active range of motion can.

So, let’s add two more terms interrelated with each other, and the terms above: flexibility and mobility. Flexibility is part of range of motion, it’s defined as  the extensibility of soft tissues, how much these tissues can extend. That can be created by passive or active range of motion.

Mobility (or, functional mobility) depends on the strength of your body, it’s the ability to move unassisted through a range. This is created by active range of motion. How strong is the muscle, can it move the joint? You can back up functional mobility with passive range, but ultimately, this depends on your strength.

While yoga has that reputation for flexibility, I suggest we shift the focus to mobility. That you might be able to pull your shin to your nose in supta padangusthasana isn’t really that useful if you lack the hip flexor strength for a daily activity (like walking uphill, or upstairs, or kicking an obstacle out of your way), or an active range in yoga (like slowly coming down from an inversion, or boat pose).