Waking up to adjust one's leg while sitting in Salaah

When I am Salah in the first sitting, I cannot point my big toe forward sometimes as it cramps up so I have to move forward and just sit with my toes on the floor. Sometimes I do it just before it happens even though it has not cramped up I do it in preparation for it. Will this be regarded as too much movement and invalidate my Salaah? I sort get half up and then readjust my toe and sit down.