Here is the official Climbing Lab position on eccentric-centric training- Never (Ever). There is no good reason. Concentric and eccentric muscle contractions are the Yin & Yang of strength training. However, people get suckered into focusing on eccentric loading because it feels subjectively harder and will leave you sore (especially the loaded, "as fast as possible" variety). I don't see much data, anecdotal or otherwise, that it improves athletic performance. If want you to "feel" like you worked out, that is fine but do not kid yourself that you are chasing performance improvements.
Eccentric-centric training does build muscle. I don't see a reason for ANY climber to build muscle. Get stronger! Yes (and more please)! Hypertrophy and strength are two different beasts. I know which one I can ride to Sendtown.
People also equate eccentric loading with slow movements. Those two do not need to be found together. Training the eccentric portion of a movement "greases the groove" but that should be done at regular speed. There is no reason to train to be slower. The best "greasing the groove" for a particular climbing movement is heaps (and heaps) of that movement. There is no reason to train the reverse engrams. One basic Climbing Lab training tenet is - You perform how you train. If your feet cut during training, your feet will cut on your project. If you primarily send during training, you're more likely send your project. If during practice, you climb 1 move, fall, and rest on the mat for 5 minutes talking to a climbing nugget, you are getting better at that (not sending your project).
Here are the practical aspects:
Don't down climb. Lower.
You should only down climb if you are training for onsights, especially of the traditional flavor. Some people claim that down climbing improves footwork. From my experience that is only true in novice climbers, but everything (and anything) improves a novice climber's footwork. Down climbing will just make you tired. Stealing time and energy from up climbing, which is the best use of your limited training time.
Don't down campus. Drop.
One of the best reasons to campus is to become more explosive and aggressive, both mentally and physically. Down campusing introduces an element of unnecessary control. It subtlety trains you to believe that you need to be in control. That is counterproductive to developing "pitbull on acid" mentally sometimes necessary in climbing.
One final note, climbing is about moving your corporeal body up. Why you want to get better at moving down?
