In the travlos (1999) study, more practice led to poorer retention and transfer test performance than less practice. a possible explanation for this result is that:

Too much practice of simple skills may result to poor learning because learners may not continue to engage in appropriate amounts of cognitive efforts, which may result in decrease capability to remember movement and poorer transfer test performance. It is recommended to have less and variable practice as to not over learn and achieve better performance.  

Ican only answer your first question, a machine is like a human body because it's a little similar. they both almost work like the same.