Load: Loading a heavy crossbow is a full-round action that provokes attacks of opportunity.
Note: You draw a heavy crossbow back by turning a small winch. Normally, operating a heavy crossbow requires two hands. However, you can shoot, but not load, a heavy crossbow with one hand at a –4 penalty on attack rolls. You can shoot a heavy crossbow with each hand, but you take a penalty on attack rolls as if attacking with two one-handed weapons. This penalty is cumulative with the penalty for one-handed firing.
Pathfinder RPG Core Rulebook. Copyright 2009, Paizo Publishing, LLC; Author: Jason Bulmahn, based on material by Jonathan Tweet, Monte Cook, and Skip Williams.