I'm standing up straight, trying to raise one knee up in front of me, like I'm marching.
I can't raise it up even to 90 degrees. See photo below. Ordinarily if my mobility is limited, I can feel that a certain muscle isn't flexible enough. For instance if I try to bend way forward I'm limited by inflexible hamstrings. However, in this scenario I don't feel any muscle being stretched. It actually feels like my hip flexors are bunched up like a squashed slinky, and the reason I can't raise my leg any more is that I can't contract my hip flexors any more.
Does anyone have any insight into why I can't raise it further, given the circumstances I described?
To clarify what I mean about my hip flexors feeling "bunched up", see image below. It feels as though there's a spring near my hip flexor. When the leg is un-raised, the spring is loose. As I raise the leg, the spring compresses until it's so compressed that I can't raise the leg further. If I instead I felt my hamstring stretching as I raised the leg, that would make sense because it would be a limitation of flexibility, but this seems like the opposite; it seems like an inability to contract my hip flexor rather than an inability to stretch my hamstring.