Can't ever seem to get core workout forms right, any for a very weak core?
I'm relatively lean(130lb, 5'8) but I have no ab definition, I think because I'm starting from a basically 0 base, but it feels like every time I try to do a core exercise my body optimizes it away or it causes pain somewhere else. Planks I can manage for a bit before my back arches and then just my back hurts. Crunches braced against a wall I feel in my core until I get a bad headache(I think from the neck stuff). Doing a leg raise(laying or hanging) I can feel it briefly in some parts of the motion until my back arches involuntarily in some parts, and again starts to hurt. I even tried swimming breaststroke but again got the form long as after 3 hours of laps just my thighs were dead.
I went to a gym on my friends membership yesterday and used the ab crunch machine, and I'm still sore in the right places, so I think that worked- but I don't want to pay for a gym membership or have to go with him 3 times a week.
Are there any exercises that are impossible to "cheat" at?