First and foremost there are two categories here. First injury the second is better known as DOMS (delayed onset muscle soreness). Here’s how you decide which you have.
Injury through exercise
If you cause yourself an injury when you’re training the chances are you will notice it either immediately, or at least within the next 2 hours post training.
What to do with an injury
If you have a major debilitating injury seek medical advice as soon as possible.
Minor injury can be self treated with a combination of heat, ice, compression and elevation. YES I said HEAT. You may be familiar with the first aid concept of R.I.C.E. (Rest Ice Compression & Elevation). Even the person who came up with the RICE concept has back down on it now. This is due to the fact ice reduces inflammation, but inflammation is an essential part of the healing process. So we start with heat for the first day, after which we can alternate hot and cold, which has a flushing effect on the effected area. Compression helps support the are while it heals but should not restrict circulation. Elevation while at rest allows blood caring the debray flow away from the area.
Delayed Onset Muscle Soreness DOMS
DOMS tends to show up 12 to 72 hours after exercise. Normal after a change of intensity or duration and is more severe with high repetition work than it is with low reps.
What to do if you have DOMS
Some studies have demonstrated Branch Chain Amino Acids reduce DOMS significantly and I personal find this to be true. There is however little proof it speeds up recovery or improves gains.
Stretching has a short term effect on the pain but you will tighten up again when you stop moving.
Important thing to note is 24 hours after the workout you are stronger, you may well still be in discomfort, but stronger. ITS TIME TO TRAIN AGAIN!!!
You will probably continue to feel DOMS to some extent for around 2 weeks after a lay of or dramatic change in training. It will get less with each session, so unless you can’t move, train.