Heel- This term is heard in conjunction with a number of phrases: “I need a crossbow with a little more heel” and “Put your heel into it”, for example. It has come to indicate a measurement of strength or exerted effort.) The latter phrase indicates a need for a crossbow with a stronger/more difficult pull and the former is similar to the Earth expression, “Put your back into it”.
The phrase originates from the loading process of a crossbow. The more powerful types of Martian crossbows can’t usually be cocked by hand, and come with foot stirrups so that the shooter can use his whole body to pull back the cable. The term ‘heel’ is derived from the fact that a shooter must place his foot or heel into the stirrup in order to stretch back the prods of the crossbow and nock the bolt.