Hurt should be a state of mind

When we exercise we are choosing which energy system we wish to work more. For some the choice is conscious, but those choosing consciously are usually a trainer or a coach. The main systems that we can train are: The cardio vascular system, the Neuro-Muscular System, the musculo-skeletal system, and the fascial system.
For most the cardiovascular system is the easiest to train, just put on your shoes and go out for a long run of more than 20 min.
The musculo-skeletal system is a close second with resistance training growing in popularity.
The fascial system is gaining a little traction after many years the medical community is finally willing to research the benefits of this little understood system trained by many athletes.
The Nero-muscular system is trained mainly by top tier athletes and strength athletes of varying degree from novice to pro.
All of these energy systems have their own degree of hurt. Aerobic activity does not hurt very much unless you are brand new. The fascial system, as we roll over knots in our muscles, hurts a little more but not for very long. the musculo skeletal system can get a good workout without much hurting at all until the next day.
The Nuero-muscular system, when taxed well is nearly enough to make you want to vomit. Heavy dead lift or heavy squats can make your system ask what hit it. A serious session at the track, either cycling or running, can do the same. An athlete of any level but the most very beginner should attempt to challenge this system at least once a week. Although highly taxing, the changes that you bring about in your body's ability to perform are enormous.
The stress of heavy dead lift or a power speed set at the track are enough to give your body a better foundation for your marathon or even 5k. A stronger body achieved through ever increasing demands is one that can adapt to any circumstances. If you did well in last year's 10k but you show up and there are Kenyans lined up to race, you may still have a shot. You will have a shot because you have done the work at the track and the gym to give you that foundation. Your head will be in a good place because you will have put in the painful work, what Brett Hoebel calls "Paying some dues." Challenge yourself under the watchful eye of a coach or a trainer then take it out on your own. Watch the noise of a painful day at the office fade into the background.