I used to work in the medical field, long since retired, and if you hurt yourself, you need to go see a qualified medic for advice. That said, I just posted a note on a friend's blog regarding a workout injury, and I thought what I said general enough to offer it here. Lot of jocks drop by, and some of 'em are getting on up there.
If you hurt yourself enough to make you grimace in pain when standing, walking, or lying down in the wrong position, you need to go to great lengths to work around this.
Do not push it.
Those guys who tell you to shove through the pain, stretch it out, man up? Where are they going to be when you are seventy and plopped in a wheelchair because you tore too much stuff up along the way?
I'm not talking about minor soreness we all get the day after we spike our heart rates, nor the bruises from banging forearms and stopping punches with our ribs. You already know the drill for those, and abide by the basic first aid acronym RICE–Rest, Ice, Compression, Elevation.
If you aren't allergic to them, aspirin or ibuprofen are useful. (While the ibuprofen will help with the pain, the primary effect for which you are looking vis-a-vis recovery is anti-inflammatory, which generally speeds up the healing process by reducing swelling and redness and all. Don't get that with acetominophen, by the by.)
If you are allergic to a drug? Break out in hives, have trouble breathing because your throat closes up, go into shock? Here's a tip:
Don't take it. Any time a cure is worse than the disease, that's a bad trade.
Back to basic physiology:
However long a nagging injury needs to heal, it takes longer if you re-injure it. Trust me, I speak both from medical and personal experience, and the personal experience is more telling. Yeah, you don't want to turn into a couch potato, you need to stay as active as you can, but if you have an injury that puts you on your back, if you can't move that body part without severe pain, Mother Nature is telling you something you had better heed. Do it, and it will cost you.
Doctor, Doctor, it hurts when I do this!
Well, then, son, don't do that ...
I used to know a doctor who treated a couple of ballet dancers. When they got hurt, he couldn't make them sit still. So he put them into a swimming pool. Swim all you want, he told them; it'll help you keep fit but it isn't weight-bearing and it will let that stress fracture heal quicker than leaping high into the air and coming down on your foot will.
Smart man. He knew that dancers have to move, so he gave them the least-damaging way he could think of.
Think of a pulled muscle or a sprain as you would a scabbed-over wound. Every time you re-stress it, it's like pulling a scab off and starting the blood flow again. This will slow the healing way down and leave a bigger scar. Scarring in a muscle or connective tissue is bad. Scar tissue doesn't want to stretch, and enough of it will cause you problems on down the line.
You never come back 100% after a bad sprain. Broken bones will heal, sometimes better than normal, if you are otherwise healthy, but torn ligaments scar, and won't be as elastic.
You can be more limber than somebody else after an injury, but if it is bad enough to scar, those never go entirely away. Look at your knee: How long has that little scar been there? If you did it when you were six and you are forty, do you think you are going to get up Sunday morning and it's gonna be gone?
Just because you can't see your Achilles tendon, that doesn't mean it isn't prey to the same kinds of processes. And they are cumulative, each one another brick on the load.
Connective tissues are notoriously slow to heal. Blood flow to joints and ligaments is relatively poor. Break your arm, the bone can be back to normal in six or eight weeks. Freeze a shoulder, you might be working that out for nine or ten months. And, as the old saying goes, bad knees you learn to live with. Better to keep them from getting bad in the first place, but failing that, knowing your limits is a good thing. There are exercises I used to do that I'm not going to do any more because they will damage something already damaged.
If you think you can work an acute injury out by stretching it slowly and gently, consider that notion in the same light as teasing a scab off slowly and gently. It hurts for a reason and going around the pain will cost you. If you have to, you have to, and you pay the price, but you will pay it.
Got to work smarter, not harder. You ain't gettin' any younger.