Help! any ideas??

Throughout this first nine weeks all my classes have been great except the sixth grade. I have sixth grade health at fourth block which is split into two forty five minute classes. By this time of the day the students are so excited, hard headed, just came from P.E.,  and  and ready to go home. It is so hard for me to grasp their attention for only a short period of time. I am  trying to include more activities in the class so they do not have to sit there the whole time, but it seems that the students do not get much out of the lesson when it is approached in activities. Any ideas would be greatly appreciated.