Train the core everyday.
Train the core high reps.
Train the core as a mover.
Train the core in order to resist movement.
Now it’s don’t even train the core: http://well.blogs.nytimes.com/2011/08/17/are-crunches-worth-the-effort/
Here is my opinion on core training: it’s just more isolating muscles. The fitness industry is moving away from triceps kickbacks and lateral delt day and towards multi joint/muscle exercises, which is nice….but the core is getting left behind in the isolation drills. Before I go further, I do think that planks, and anti rotation work, and even some crunches/bicycles etc (gasp!) have a place in every beginner’s/not consistent exerciser’s training regimen. These folks may lack the base of core strength needed to perform complex drills. I really think that core training is akin to corrective exercise in that it is needed until its not needed any more. (Yeah, I’m a smartsass) Why would I need to plank for 3 minutes? Nope, progress that drill. How many reps of bird dogs do I need to do? Progress that drill. 100 crunches? Progress that drill!
The core is part of your whole body, and is going to be challenged in that system when training multi joint exercises-that’s why I believe once a certain baseline of core strength is reached, it may not be necessary to continue to directly train the core. Here are some of the drills I regularly throw in to my training which aren’t direct core exercises-yet do provide lots of stimulation. Front squats (both barbell and single KB), suitcase deadlifts, bulgarian split squats loaded one side at a time, all types of medicine ball tosses, odd object (stones, logs, sandbags, people) lifting, uneven carrying (my favorite), single dumbbell presses of all types and single arm pulls of all types. This isn’t a full list obviously, but while these aren’t direct core work-they certainly challenge the core.
Now-if you enjoy specifically training the core, I don’t think anyone would ever say that’s a bad idea. This is different than other isolation exercises in that if you really like your chest day, and you do it all the damn time, you end up with asymmetries that can be problematic. However, if you keep performing core centric exercises, I can’t see any issues coming out of that. So it becomes a personal preference and time issue-you may not need to dedicate extra time to the core if you are already strong and performing intelligent and challenging full body drills.
Here are a couple of ideas on how to progress some common drills and make them more challenging.
Instead of crunches do Turkish Get Ups. A crunch is only the beginning of sitting up and standing-so why would we keep training only partial parts when we’ve reached a certain level of strength?
Instead of static planks, hold a plank and row. But row heavy! Keep those hips level.