You should know your limits when you run. So, the Fraunhofer Institute in Germany, along with scientists in five European countries have developed the Runsafer smart running shoe. It uses built-in G force, direction and GPS sensors to determine how hard, how fast and how long you're running.

The best part? It'll tell you when to take a break. But wouldn't your legs already tell you that?

The shoe will transmit data to your smartphone via Bluetooth and it connects to a central computer that will analyze your running information. You'll get tips sent back to your phone suggesting ways to improve your workout.

The system will also analyze the way you plant and push off from your feet. The Runsafer smart shoe is still a work in progress, but the Fraunhofer Institute says they hope to see it developed into a product you can buy in 2015.