for long sitting meditation: my favorite stretch for hamstring and hip opening

The movement is demonstrated here,

https://drive.google.com/open?id=1n_K1PVor1nxbGPCdBAuZUDrYoGeA_ZGL

note: Even if you're flexible enough to not use a strap, it's good to get in a habit of using it, for times when it's cold you're not warmed up to full range yet, but also because the length added by strap gives you more angles to find tight areas to play with.

Why this is my favorite stretch for hamstring

Especially if you have lower back  pain issues,, when doing hamstring and hip opening stretches in other postures like standing, or sitting, it's easy to strain the low back. But from the supine posture, lying on your back on the floor, the floor supports your low back, acting like a brace that prevents  accidental strain.

My version of it 

Instead of holding each pose for a longer period of time, like 9 slow breaths, or a few minutes, what I prefer to do is 3 normal breaths for each pose, but cycle through them at least a few times, so spending several minutes cumulatively on those 6 poses (3 for left, 3 for right), but no more than 3 long slow breaths for any pose. This is to balance heat, qi, flow, and maintain elasticity of muscle and tissue, especially those of who have a tendency to have a cold body type.

customize it

But you have a different body, you may have different needs, so experiment with the timings and what is the optimum combination for you, in balancing heat, flow, elasticity.

Here's the radical part: Subtle Medusa rules heaven and earth

Once you get the hang of the move above, here's my innovation and improvement to the move. While the leg and hip is static during the stretch, you have several other body parts that you can do small circular or simple movements that change the angle of stretch of the leg and hip slightly, finding new tight patches that you wouldn't discover if you do the same 3 fixed positions every time. But more importantly, you're developing silk reeling, qigong movement skills on other body parts at the same time as you're getting the stretch on the leg and hip. So it's like getting 5 great exercises for the price of one. For example: During any of those 3 poses, I could be slowly turning my head side to side, making wrist circles, shrugging my shoulders, flexing my feet or making foot circles, etc, all simultaneously.

Another variation

instead of just using the 3 positions, the leg straight up, all the way to the left, and all the way to the right, you play with other angles just slightly off, or anywhere within the 180 degrees. Don't just always pick the 3 orthogonal angles.