Most people use the nano for fitness, so Apple has improved the fitness experience. No extra sensors or equipment ins necessary. Nano now is equipped with a built-in pedometer, monitoring your speed, distance, and past workouts. The accelerometer also monitors calories burned and helps you set up goals to meet each day. No extra sensors or equipment ins necessary.
When you are at the gym, look for Nike + iPod compatible cardio machines, so you can connect your iPod and keep track of your workouts. Also, you can go back home, plug your nano in, and upload all the data from your own run to the Nike+ website to monitor your improvement over time.