Shanty is,...... let me see how many answers do you want?
It's a work song
from the word base chant (cf French chanter chanson etc)
it is a well known aerobics phenomenom that excercise to music allows 15% more energy to be expended. Because of anticipation and enjoyment. With shanties the act of people all pulling together at the same time (as per shanty rhytm) made the work more efficient as well.
thats a short answer - there are much longer ones!!!!!