When you exercise to the point where you cannot inspire oxygen fast enough to deliver oxygen to your cells, your body starts creating energy (in the form of ATP) by anaerobic respiration as opposed to aerobic respiration. A by-product of anaerobic respiration is lactic acid, which causes pain to muscles. Over time the 'oxygen debt' is repayed and the lactic acid and the pain will go away.
Some of the pain may also be attributed to the small tears that occur in muscles after a hard work out (this is natural), and will also go away as the muscles rebuild.
sometimes
Fin-tastic!
stop the exercise
Many things make you stiff, like walking too much, sleeping on the wrong side, and others.
Because you have an erection.
Sometimes, depends of what I feel like playing.
You can't let it rest and feel better I get a stiff neck about once a month and just miss a game it's worth it
possibly because you past your limits, exhausted or dehydrated.
so they realize that they need to get a drink.
Because sometimes the joints are stiff and when they are cracked it relaxes them. Cracking them also releases endorphins in your brain. Endorphins make you feel good. Their released during sex too. It's not harmful or anything it's just bubbles in the joints being popped.
Burtons feel rating is a stiffness rating for snowboards. 1=super soft 10=super stiff you will want something softer if you are into jibbing and rails. You will want a medium to stiff board for jumps, half pipe and freeride.
Rheumatoid and osteoarthritis can both do this.