In the case of a dock high C or D unit, there is very little if any freight lifting involved, most freight is loaded and unloaded by the locations. But at times it does help to have some strength to horse stuff around. I have a pallet jack on my truck and use it a lot, and I can vouch that it is very advantageous to be in decent shape and have some upper body strength when expediting with a C, D or E unit. Not a necessity, but you will help yourself on many occasions being able to move at least 50-60 lbs or so when owning a truck. If health and strength are a major issue, you will be better off running in a van.
-Weave-