My guinea pigs will not move HELP!?

my guinea pigs just sit there and snuggle together. I put them outside in a run and they just huddle together in the corner and it is the same when i let them run round the kitchen and again they just huddle together and don't move. I don't want them to get fat and stuff so i want them to move but they just won't. I have had them for about 5 months. what can i do to get them to move. They have the whole kitchen to run around in but the choose not to i need help!!!!!