I'm rather flexible, but still cannot do the splits. I'm trying to do a static stretching about three times a week, and about 30-60 minutes every time.
But I noticed, that when I'm trying to stretch with my body parallel to floor - holding body on my arms and legs on sides, stretching - after it I feel uncomfortable in my knees. When I'm stretching with my body upright, leaning back on the wall, and my knees looking up, all is good - no pain in the knees.
Is first way harmful? Or just my knees are still not ready?
According to @JohnP comment: good highkicks in my understanding are highkicks I can manage without body incline, with light warming, on a heihgt about 200cm(I'm 186cm), striking with my shin - not with foot lift. Splits will make it real.
Along with splits stretching, I'm trying to stretch splits-transfers - to move from right split to horizontal, and then to left - that helps heavily while turning leg for striking.