I still think this is a brilliant idea to strengten, and learn, the core aquatic skills. especially for activating muscles you normaly dont use much. Also for locating the right muscles used for kicking from the hip and not the knee.
Some Ti coaches have said he is driving the rotation with the arms, but its the opposite. . The legs lead, the arms follow. He is driving the rotation from his legs.
Only when arms come above water weight is pushing them down, and then thats hard to hold with the legs.
Thats some fractions in time where arms starts to lead rotation.