Often I hear from certain "fitness professionals" that training (with the above goals in mind) doesn't have to hurt. That's completely untrue. (I really wanted to say "This is pure bull****." but some people feel that it would make my content less credible. Only for the less discerning.)
Based on the items I have mentioned below (in previous posts), if we are constantly evolving physically, we should expect to be in some form of constant pain. In fact, true fitness experts will know that they are truly pushing their boundaries ONLY when the state of pain exist.
These fitness practitioners constantly look for that pain and discomfort and their perspective on this "pain and suffering" is a positive one. They look forward to it.
No pain. No gain. This is the truth.