MN/SE5 -- L-sit -- Form check

L sit 

https://www.youtube.com/watch?v=OeTS9eAYWqs&feature=youtu.be

L sit 2

https://www.youtube.com/watch?v=ROvpgXNrCwY&feature=youtu.be

I get this huge knot on the top of my quadriceps about 10 seconds into L-sits (and other exercises that require that super engagement of the quads and core, but none like the L-sit where the hold/engagement is so long).  The knot is just a bit higher than the mid-point of my femur and seems to be in the belly of the muscle (hard to see in the 2nd video but it is about the size of a large grape and protrudes past the skin).  Intense pain dissipates almost immediately when I stop and the knot goes away within 10-15 seconds.  I have tried stretching the quads and hamstrings before doing it.  I also tried the Magic Wand Coach Summer talks about in Tim Ferris’s book.  I stop because of the pain where the knot is, not because of strength.  Is this engagement one that requires "compressive" strength in the quads.  Is it a form issue?  Any ideas or suggestions?

Hi JIm, welcome to the rectus demoris cramps world! remember to stretch them, the more the hamstring are flexible the more you can work without cramps. And point your toes.

Thanks!  I was afraid of that!  Of course, pointing the toes intensifies the pain, but I will comply!