At the beginning of exercise strength is often good, and then it steadily declines with increasing effort and, in severe cases, patients are weak all the time; they can't see properly; they see double; their eyelids droop; they can't hold their heads up; they can't chew; they can't swallow; their arms and legs are weak; they can't peg out the clothes on the washing line; they can't walk upstairs, and in really severe cases they can't even breathe — unless they're supported on life support machines they would die.