I started pilates in September and have been mostly doing reformer classes with the odd mat class thrown in there. My abs have certainly gotten a nice shape to them now and I think I've made modest progress overall but one thing I notice is I get the "shakes" so easily despite having 50 classes to my name.

It's the lower abs I think. There sre various exercises that involve them and I notice literally immediately they shake with each repetition. I can get through the exercise but I'm left wondering are they not being strengthened? Why am I so seemingly weak here still.

I do get shakes in other body parts too. Overall a rather tense person and not big or strong but reasonably fit. Just in case that's relevant.