Aerobic actions were recorded from subjects using the Inertial Measurement Unit (IMU) on an Apple iPhone 4 smartphone. The IMU includes a 3D accelerometer, gyroscope, and magnetometer*. Each sample was taken at 60Hz, and manually trimmed to 500 samples (8.33s) to eliminate starting and stopping movements. iPhone is always clipped to the belt on the right hand side as shown in the picture.

Note:
* Our experiments show that the data from magnetometer is not useful. After feature selection was performed, the most useful features came dominantly from the accelerometer data.