You have seen me post before. My 13 month old has a weak core and hips. He has not yet been diagnosed with anything (my pedi thinks nothing is wrong except weak trunk) but anyway, he has army crawled within only pushing off of his right let for 3 months now. Yesterday he finally did some "normal" crawling and alternating each let and when he gets into the sitting posistion he usually bends his left leg to do it which is great! He will only do normal crawlng for a few "steps" but if the object is far, he is back to army crawling -- I assume because for him it's all he knows and it's faster for him. I am so happy we are making progress!!!