If you notice that your movements are not properly registering, please try the following steps:
1. First make sure you are following your trainer as closely as possible. This includes speed, position, arm & leg movement, etc.
2. Use the Kinect tuner to calibrate your settings. You can access the Kinect tuner by pressing the Y button on your controller at the main menu. For more Kinect tuner assistance:
3. Try repositioning the Kinect Sensor (at least 2 - 6 ft. from the ground, usually directly below the TV or on top of the TV).
4. Try standing different distances to and from the sensor (6 - 10 ft. is ideal).
5. Try adjusting the lighting in the room. Minimize side or back lighting and avoid positioning the sensor or player in direct sunlight.
6. Black clothes & very baggy clothes can also cause bad performance.
Here are some external links with more info:
Xbox Support Kinect page