The simplest way to overload a set of 3x3 is to climb with a weight belt. Another way of overloading is to down climb all the problems. To down climb one set of 3x3 is a good landmark for anybody who wants to create power endurance in a short period of time. This is the method I use to train my power endurance. I automatically double the amount of moves while inherently increasing the intensity of my session. Down climbing routines should be done on problems 2 to 3 grades lower than you project.
Back to weight training. There are basically three ways of doing so with traditional weights.
1-Increase weight
2-Decrease time between sets/reps
3-Increase number of sets/reps
In climbing, there are also three basic ways of beefing any sport specific routine.
1-Increase weight-wear weight belt or vest
2-Decrease time between sets/reps-decrease interval time between climbing sets
3-Increase number of sets/reps-Increase 3x3 to 4x4
But there is also another way of seeing it:
1-Use open hand grips (slope v.s Pinch)
2-Increase pitch of wall (Slab v.s Roof.....epic rap battles anyone?)
3-Increase number of continuous movements (Down Climb)
Developing the Pyramid Program
A well developed Pyramid program will have climbs on different angle walls Also, keeping note of the number of moves and hold selection are both methods of quickly changing the intensity of any given set. Subbing out a V2 on jugs with a short pinchy V3 problem will help develop compression strength= while maintaining the same number of climbs/moves in your session.
Nature Abhors a Vacuum
But we need an easy, repeatable method of observing personal limits and boundaries. In building a climbing gym routine, a climber is essentially sequencing the same amount of movement from session to session all the while adjusting the intensity of their sets according to my training cycle.