Two Squat, Two Pike

I have a question about pikes. 

Where should the stretch come from when doing pike leans? The hamstrings mainly? Some lower back too? Both? 
Related: should I keep my back arched (straight) while piking? (Then most of the stretch will be in the hamstrings?)

I ask 'cos I think I got the balance wrong, did more in my back than in my legs. It didn't feel right for a few days. 

Hi Samin,

Great question. Depending on your current level of flexibility, you will feel this exercise stretch in different areas. Most commonly, Standing Pike will be felt in the hamstrings and lower back, but if flexibility is an issue for you, you might even feel it stretch through the back of the knee as well as in the calves. As you stretch, focus on keeping the spine straight in order to isolate the correct muscle groups. It is okay to feel this stretch throughout the lower half of the body, but be careful not to push too hard. While you should work hard on your stretching, it should never be painful.

From what I read many times on the forum and from what I m doing myself you should keep APT (anterior pelvic tilt). That means straight back maintaining the natural arch in your lower back. You should feel the strecht in your hamstrings, not the lower back. APT will help you on this. Actually what I ve read is that when one is not able to keep APT at 90º when doing pike you should not flex your spine because one is at risk of injury. So it s better to put your hands on your knees or wherever is necessary to keep APT and don t flex the lower back. 

What I do sometimes is placing my hands on a stall bars higher and that help me maintaining APT.

Edit: I mean I read keeping APT only when the hamstring flexibility is quite bad, like me.

Thank you @Jeffrey Bittner and @Antonio Alías Montoya: keep APT, keep spine straight; stretch in the hamstrings not the lower back.