Is it important to hurt during or after training?
But probably not.
If you're new to exercise, or at least new to a particular type of exercise, then you might feel a little discomfort in the days that follow, and that's pretty normal.
Once you've got yourself in to a regular training groove however, the discomfort will be less, and this is good.
Because it means you can train more, and perform better (in either life or sport).
Where you should never feel pain, is in your joints. If what you do is hurting your ankles, knees, hips, spine, shoulders, elbows, wrists... stop doing it.
Where you might feel pain is in your muscles, and usually this will follow exercise that involves resistance training, hard running or jumping.
This will be because of the landing or lowering action your muscles experience, and for a trainer it's really easy to do. If a trainer wants you to hurt, then generally you'll have jumping in your session, and exercises that involve you performing between 10 and 25 reps, focusing on the speed of each movement.
And if you hurt in the right places, it means you're getting results in the right places.
Well no, it really just means you hurt.
Let's take the crunch or sit up for example. We can make your belly hurt for days. It will be so sore it's difficult to breathe, and the idea of laughing or coughing makes you really nervous.
But you've just performed and exercise where most of your body is on the ground. How challenging is that really? How much energy will you use?
Don't be fooled by pain, sore muscles don't mean smaller tummies, smaller legs, or smaller arms & legs. They just mean sore muscles.
If you are a body builder (someone who trains with weights 4-20 times a week), hurting might be good. Pain in this context could mean you have caused enough trauma in a muscle to stimulate growth.
If this isn't you, you don't need to hurt. You just need to enjoy what you do, and feel that sensation of knowing that you've done some good following your workouts.