This is a saying that is heard often in gyms and other types of training halls. I would like to say that its quite inaccurate. If you are experiencing pain, its very unlikely you will continue training to make gains. Pain at its very basic level is your body signalling that there is something wrong or that it has suffered some type of trauma. The distinction I want to make here is that there is a marked difference between pain and discomfort. In addition every persons pain threshold is different.
When we are referring to making gains (i.e. growing stronger, moving more weight, being more flexible, adding muscle, greater cardiovascular capacity) there will be times when we will experience discomfort. The body being the amazing adaptive machine that it is, requires us to stress and push it if we want to make significant gains in certain areas. What we may consider to be pain may only be discomfort. When I train students, I always tell them, pain usually stops you in your tracks, while discomfort, allows you to work through it.
This is not to say that you cant train while in pain, and certain situations may require you to work through the pain. These occurrences however are not the norm and you should listen to your body if you are in pain.
Discomfort on the other hand should never stop us. If we let it, we will find ourselves making excuses at every turn because we are no longer in what we may consider our "comfort zone". This not only applies to training, but to life. You will never have any gains as long as you remain in your comfort zone. In order to grow you have to stretch yourself, try new things and be willing to risk the comfort.
Any new endeavor will have moments of discomfort, that is when you are growing. Any training regimen contains moments of discomfort, if you are not willing to work through them you will not see the gains on the other side.
Ultimately the decision is ours to make. Are we willing to be uncomfortable in order to grow and make gains in every part of our lives, or will we strive to remain in our comfort zones- comfortably stagnant?
strong spirit-strong mind-strong body