Well I'm 40 and trying to come back afther several years of inactivity, it could be the rust in my joints,bones and muscles jejejeje!!
Even it hurts (every day) I won't go back cause it will worse in a few years more, so I rather prefer some pain now that a lot of pain when I go to 60. Is there some medicine to ease the lactid acid? I think I'm gona buy some ankle elastic device (sorry don't know the name in english) to compes a litle my ankle joint and feel more secure.
Manny
I'm no expert on workout physiology, but like some of the other Grumpy Old Men who've already posted, I
am old.

So, here's my experience with types of pain and what I do about it:
Muscle pain, from exercising specific groups (as in doing push ups). Lactic acid builds up, and as others said stretching, Advil, soaking in the tub can all help.
Bruising: Doesn't happen so much after a certain number of years training, but I've always ignored it. The better the circulation, the faster the pooled blood (hematoma) disperses back into the body. If it's really bad/painful and accompanied by swelling, ice for the first few hours can help.
Joint pain: I'm very careful of this. Joints don't heal well, if at all, once they're pushed too far (and I've pushed too may too far already

). The same remedies as for muscle pain help in the short term, but for long term, I work to build the muscle groups around the joint to take more of the pressure. Example: for my terrible knees, I do stance work and forms (don't even wear braces anymore--but don't do a lot of rolling around on the mats, either: no sense tempting fate). For my chipped and ground-down C-3 to C-5 vertebrae, between which the nerves have to reach the arms, etc

, again try to build the trapezium muscles, and those around them. Helps immensely (and if I get lazy and don't do these, Oh boy!).
For broken/deformed bones (old breaks), to keep the arthritis manageable, just have to keep active. But not like I'm a kid of 35 again--that would be reckless. The alternative as several have said, is use it or lose it.
Anyway, hope my experience might help a little. :asian: