Lifting into Yoga Headstand with legs straight is perhaps one of the more challenging ways of getting into headstand particularly if hamstring flexibility is limited.
If this is the case, then you might want to look at hamstring stretching yoga poses to improve your hamstring flexibility.
Despite having tight hamstrings when I first started yoga, I was determined to learn how to lift into yoga headstand with my legs straight. I didn't learn to how to do headstand using a wall, nor did I learn it first with knees bent, I went the hard route.
I spent about three months practicing headstand and failing. I'd get my legs a little way up, then roll out. Then I'd get a little bit higher. Then same story again, I'd roll.
As I learned to get my legs higher I'd get a taste of balance in yoga headstand, a false sense of "yes I have it" and then I'd roll out.
Of course now, even though I don't practice it all the time, yoga headstand seems to be mine to keep.
A lot of students want to get up into yoga headstand with legs straight straight away and don't seem to understand that it can take a lot of work.
Unless you are very aware, unless you have spent a lot of time practicing feeling your body and controlling it, you probably won't be able to lift up into headstand with legs straight without a lot of practice.
That being said, if you want to approach it logically, with a modicum of discipline, if you want to learn headstand and learn how to feel and control your body at the same time then read on. Even following the steps below, you will probably fall alot, but you may find that you progress faster while still gaining body awareness and control along the way.
I've got a four year old daughter. I take her swimming a lot. And I always keep an eye on her when she's in the pool. For a long time she's been big enough to touch the bottom with her feet but she's not yet gotten comfortable with putting her face under water. So I keep an eye on her because I know that if she trips she'll panic because she doesn't like being underwater.
Then one day she was jumping around and her nose accidentally went underwater. She noticed this and also noticed that nothing bad happened. She then voluntarily dunked her own head under water. From that moment on she's been playing more and more with her head underwater. Even though she can't yet swim she's comfortable enough with her head underwater that it's not a problem. Now she's learning to float, and now she's even learning to swim with her head underwater and I don't have to do a thing.
If when learning to swim you aren't afraid to put your head under water then learning is a lot easier. You can focus on moving your body through the water instead of just focusing on keeping your head above the water.
Lifting up into yoga headstand with legs straight, or even just doing headstand in general, you'll learn a lot faster if you aren't afraid to fall. And so that can be the first thing you learn in headstand training, how to roll out.
When you do headstand with your fingers clasped behind your head, as opposed to tripod headstand, the first thing you do is relax your fingers.
The next thing you do if you feel yourself about to fall on your back is that you round your back. Then you roll out of the headstand instead of doing the equivalent of a belly flop on your back.
Practice doing a simple forward roll, then practice rolling with your hands in the "yoga headstand" position, i.e. fingers clasped behind your head.
And for comfort use some cushions.
Also make sure that where you are rolling is clear of obstacles.
Okay, you've got the rolling out of the way.
The picture below shows the different stages of going up into headstand with legs straight.
In all the above pictures the blue line is drawn against the edge of my knuckles.
From 1a to 1b my pelvis moves towards the blue line or past it to help balance the weight of my legs.
From 1b to 4 my pelvis moves away from the blue line so that I don't roll back.
Now it's all very well me showing you pictures of what to do. How do you know that you are doing these steps?
I believe that the most efficient way to move towards headstand with legs straight is to practice these steps in isolation.
Starting with weight on your feet, you can walk your feet towards your head to the point that your feet become empty.
At the same time you can work on stabilizing your foundation. In this pose the most important part of the foundation is the arms, shoulders, head and neck. As you walk your feet towards your head practice using your shoulders to press your elbows into the floor.
If you press your elbows into the floor, then when you walk have your feet close enough to your head your feet will become empty. When you can feel that your feet are empty while at the same time your shoulders are active so that your elbows are pushed into the floor, then you are balanced.
What I'd suggest is practicing walking your feet towards your head and way from this while feeling your shoulders, elbows and feet. Once you are comfortable and can feel when all of your weight is over your foundation, then you can rest or move on to the next stage.
By the way, your head and neck also form a part of your foundation. As you move back and forwards in stage 1 of getting into headstand with legs straight, make sure that your neck feels comfortable. Make sure that it is level from left to right and also from front to back.
For front to back tilt of the head, you can try tilting your head slightly forwards or slightly back. See which position feels the most comfortable.
How should you move when you do the above exercise or the ones that follow?
Slowly and smoothly. Smoothly walk your feet towards your head. Smoothly walk them away from your head. You not only practice feeling your body and controlling it, you also make it easier to stop your self if your your neck, or any other part of your body feels unsafe.
In a balance pose like headstand you need a stable foundation. But you also need it to be soft enough that you can feel where your center of gravity is. Your foundation needs a bit of softness so that it can make the necessary adjustments to help you stay balanced.
For now focus on pushing your elbows into the floor. This is critical for lifting your legs.
As you move to the next stage of headstand with legs straight, lifting your legs to horizontal, push your elbows into the floor. But also push down with the sides of your hands. And press down with the crown of your head so that you neck has tension (to help keep it safe.)
To lift your legs to horizontal your butt has to move back. So you can practice moving from feet on the floor (1a) to legs horizontal (1b). Just move between these two stages. Work towards pausing with legs horizontal. This is important so that you can learn to feel your butt as it moves back and also so that you can learn to feel your foundation. You know your butt is moving to far back if your hands start to press down with more pressure. You know you aren't far enough back if you elbows have more pressure.
If your hands have too much pressure push then into the floor to help push your pelvis "facewards" or forwards. If your elbows have too much pressure push them into the floor to push your pelvis "buttwards" or backwards.
In both cases stop when you feel the pressure is even between elbows and the sides of your hands.
Once you are comfortable getting to legs horizontal, try moving to step 2, legs at 45 degrees.
For this stage of moving into headstand with legs straight I'd again suggest starting with feet on the floor. Lift to horizontal moving your pelvis backwards. Pause. Then move your legs higher while moving your pelvis forwards. Notice your foundation. Move slowly.
Stop and then lower to horizontal moving your pelvis back. Then lower all the way to the floor.
Once you are comfortable with moving to step 2 then steps 3 and 4 are more or less the same except your are lifting your legs higher.
The final stage is learning to feel when your legs are vertical.
For this practice feeling the front of your hip joints. While standing slowly hinge forwards at the hip, then slowly stand up. Notice the feeling in the front of your hips when you are perfectly vertical. Try to find that same feeling in headstand.
Once you are comfortable with moving your legs up into headstand with legs straight and down again, you can try moving smoothly up to legs at 90 degrees, pause, then to vertical, then to 90 degrees and pause again, then to feet just above the floor, then touch the floor and relax.
After headstand you may find it helpful to side bent, twist, front bend and back bend your neck.
You may also find it comfortable to do a standing forward bend with your neck relaxed so that your head hangs freely. Think of this as decompressing the neck.
You can also do shoulder stand.
How long should you hold yoga headstand?
I'd suggest working slowly towards 5 minutes. Notice how you feel after doing headstand.
If you have time, 10 minutes may also be worthwhile. But be very aware of your neck. If you notice neck pain, then desist. A more sensible approach may be to go up into headstand, hold for a minute or so, come down and rest, then repeat.
If you want to spend more time upside down without overworking your neck, I'd suggest doing other inverted yoga poses like handstand and pincha mayurasana.
When clasping your hands you can have your palms open and cupping the back of your head, or you can have your palms together. In both cases make your wrists strong. Try both options to see which works best.
Also tuck your bottom most pinky inwards so that the outer edges of your palm can lay flat on the floor. You can also try switching the interlace of your fingers each time you practice moving into headstand with your legs straight.
For a more thorough introduction to balance and some options for practicing headstand that don't include moving into it with legs straight, take a peak at Balance Basics.
You can preview it on Amazon.