Problems with swimmers, back bows and the like


I have severe issues with any moves like those mentioned above which involve lifting the thigh off the ground. I can't do it, I just lay there like a potato wondering why my legs won't lift. I can lift them one at at time, but it's slow and clunky, and they always have to be lifted from the ground - from a hover position is just impossible. My arm movements on these moves tend to be okay, it's really the legs I come apart on.

Can anyone help with what the issue may be please? I'm suspecting I have a weak lower back and my back extensor muscles need a lot of work. My ab/oblique muscles are fine (undertrained sure, but capable) and I have no issues with strength training on my back (rows, deadlifts, etc.). It's just the pilates/yoga style lower back exercises which I have problems with.

If anyone could offer pointers or advice or thoughts, I'd be really grateful. It's so annoying, especially when my boyfriend, who does zero exercise, just lays on the floor and pulls them off perfectly and easily -.-