What Are Symptoms Of Muscle Disorder In A Child?

Yes My 5 yr old son has just started prep and has already completed his first yr in kindergarten. He has had the same teacher for both years. I was informed that jesse is having abnormal issues in holding a pen/crayon and we a wondering if this may be a muscular problem. I have also noticed when during his swimming lessons he appears to show some muscle anxiaties in the arms. I am fully aware this could just be verves but it is clear there is no relaxed movements in his arms. Iv also pointed out to his teacher that he clearly finds it hard to push bottons example when on the bus and we need to get off cant push botton and padestrian lights ect all indicating the pincer grip, which he needs to master in order to write