I wanted to bring attention to a phrase that is very much overused & misunderstood in the fitness & wellbeing industry:
There is no such thing as "core strength". What most trainers are trying to refer to is EFFICIENT CORE SEQUENCING AND FUNCTION. Unfortunately not everyone has the knowledge to have a real understanding of what this is. And therefore the vast majority of trainers put their clients on fitballs; force them to plank; get them attempting multiple manoeuvres whilst balancing on a bosu all in the name of "core strength".
Now I'm not condoning these movements altogether BUT...
...The problem here is that if an individual who has inefficient core function does these exercises they are more likely causing harm than good. If someone has an inefficient core to begin with, no amount of "core strengthening" is going to fix that. You can't out-train an inefficient core! You are only going to be putting more strain on all the areas that are already under strain due to the inefficient core function.
Did you know just about any exercise can be a "core strengthening exercise" if done with good core sequencing (squatting/deadlifts/ lunges/pullups etc)? Your core muscles are the first thing to activate when you move at all. Lifting your arm off your lap before you reach for a cup of tea activates your core. Picking up your foot off the floor in a seated position activates your core. Breathing activates your core.
Achieving efficient core function is going back to extreme basics i.e. breathing technique as well as a series of very "back to basics" core sequencing exercises. It is also very important to know where the dysfunction lies in an individual to begin with, there are many core muscles in the body all working together for different purposes.
If you are looking to get a better functioning core musculature, and particularly if you are experiencing pain, please think twice before signing up to just any "core strengthening" programme or class. You should be getting individual attention!