In track and field, which part of the body has to cross the finish line to stop the clock?

Question

Is it any part of the body?

Answer 1

Chest or torso, NOT any part ! You can't throw your arm forward and win !

Answer 2

Any part of the body

Answer 3

Actually the "torso" is what needs to cross the finish line. The runner actually breaks the "plain" of the finish line with the torso and that is when their time is calculated.  A hand, foot, head, etc. does not count.  The timing is usually done by digital photo timing such as "finish lynx"  That was pretty basic but it answers your question