This classic yoga pose offers a lesson in the workings of the deep core. Full Navasana is difficult to do correctly and I always teach it first with the knees bent. Most students can get length and extension in the in the spine with the knees bent. If the lumbar spine starts to round backwards as you try to straighten the legs to full navasana, you’re moving to far too fast. Students can do great work in this type of boat pose even holding the back of the thighs if needed.
Full navasana pose requires length and balance in the hamstrings and quadriceps. Tight hamstrings and lower back muscles often make the rectus femoris tendon that attaches at the top of the thigh seize up. If you can work with a tiny arch in your lower back and a neutral spine and straighten your legs navasana then becomes a stretch of the rectus abdominis. Readers of the blog can imagine that I don’t like that much as I think everyone’s rectus abdominis is too long to begin with (But that doesn’t mean that they don’t need tone).
The lesson about the core that I mentioned in the first paragraph comes in the transition from full navasana to half navasana. If you have the length in the back body to assume the full shape of the pose than navasana won’t much work at all because you would be held aloft by the tone of the psoas major. The engagement of the psoas keeps the curve in the lumbar spine which supports the length of the spine above the lower back.
You can get a sense of this when you begin to lower from full navasana to half navasana. There reaches a point on the way down where the psoas will let go, the spine will lose its curve and the abdominal muscles will kick in for real as they work to support the spine. Move back to full navasana through the arch of the lower back and watch the effort go away.
I often demonstrate this in class using the sound of my voice as a guide. I can pretty much hang out in full navasana and chat away in a normal tone but as soon as I make my way into half navasana I can’t keep the effort out of my voice which is a cool thing to hear. Try going back and forth from full to half navasana, even if you have to keep the knees bent, and try to feel what happens in transition from one pose to the other.