more and more scientific experiments prove that physical exercise can reduce the danger of some illnesses in middle-aged persons. exercise strengthens the heart muscle, reduces blood pressure and helps to prevent muscles from changing into fat. physical exercise is just as important for children. exercise and food affect growing speed in young lab animals. baby mice start running as soon as they are big enough to use an exercise wheel in their cage. if they get extra food and run a lot, they will grow as much as 1.5 times bigger than normal. the same differences in growing speed might be found between active and inactive children. physical exercise helps active children grow faster than inactive children. one experiment shows that the brains of the mice that had enough exercise
