Our group was given an Arduino-board as well as a Piezo-sensor and some LEDs.
We had complete freedom to do with it whatever we wanted so we placed the piezo-sensor inside a boxing bag and connected it to the arduino and the arduino to flash.
I then created a flash-interface which took the information from the and which gave me an indicator for impact and strength of impact.
The game I created then was to hit the bag as often and hard as you could in 10 seconds. Every punch gave a score according to the strength and all punches added up to the final score. You could also play it for a longer time but most users are very short of breath after just 10 seconds of intense hitting.
While you were punching a voiceover made fun of your punches in a cockney-accent to push the experience even more.