Working out causes a lot of physiological changes to the body way before it causes physical ones. When you begin a training program, most noticeably changing is the water weight in the body and an increase in soreness a day after the training session. This is known as delayed onset muscle soreness, or DOMS. DOMS is caused by many microscopic tears in the muscle and the fluid accumulation in and around the damaged tissue as it tries to repair itself. This can also happen to well trained athletes after an unusually tough session.
DOMS signals that there was something done to the body, the most noticeable cue training can give you. But you need to be aware that even if you train weights and do not get DOMS, you still have damaged the muscle. Explosive exercises like sprinting and plyometrics can also cause muscle damage. The muscle damage we are referring to is not bad, it is the result of tension tears caused, more often than not, by the eccentric phase or negative of the lift. It is the part of the lift that the muscle lengthens again with a load applied to the joint. As the body slows the weight, the fascia and the fibers tear slightly if the load is too great. This phase is most often over-trained by the general lifting public because of the following of bodybuilding routines drug enhanced athletes do.
Do not get me wrong, negatives are necessary for the muscle to get bigger, in fact it really is the only part of the lift that causes hypertrophy after the session and as healing begins. It is what you do and eat directly after the workout that can decide how fast your body heals, and some research is even showing that during workout nutrition may have a large part to play.
Let me state this loudly: You are only as good as your post workout nutrition. You do not get bigger in the gym, you do not get faster in the gym, you only perform the exercises that cause the body to adapt to the overload you have given it. If you continue to give the body PROGRESSIVE overload, you get progressive results.
The key is to stop catabolism, or muscle breakdown, on a hormonal level as fast as you can. After the workout out, cortisol levels are through the roof, and you need to replenish liver and muscle glycogen before protein synthesis can occur. Once you stop breakdown and balance your blood and muscle sugar, you have won most of the battle. Now its time to rehydrate and keep giving the body what it needs: protein.
Eat as soon as you can after training. Get a good balance of carbs and protein. Some schools of thought think that post workout supplements are crap, whole foods are better. I personally like to drink a shake, fruit flavored, after the training session because after I work hard, I could not stand the thought of eating! My stomach is a mess and I am on the verge of puking.
Point being, get at least 30 grams of carbs and 30 grams of protein after your session. You will be well on your way to jump starting the healing process, getting you ready for your next session.
You truly are what you eat.