You can work out all you want, but training isn’t what creates improvement. It’s how your body recovers from that training that matters. (Learn the Value of Rest and Recovery to Sports Injury Prevention and Treatment.)
If your muscles aren’t getting sufficient rest, or are being overly damaged during your workouts, then they can’t fully rebuild themselves—meaning all of your efforts will actually make you weaker, not stronger. To understand the importance of recovery and how it can be maximized, here is a brief look at how your body functions in terms of rest and recovery.

The Effect of Training on Your Body

When you work out, you’re essentially inflicting damage on your muscle cells. The human body is programmed to rebuild these cells to a slightly higher level, so that less damage occurs the next time you’re subjected to the same workload. In building strength, you are changing your body a few molecules and cells at a time.
It takes time for the body to rebuild damaged cells. Once your body finishes this regrowth, the new molecular structure sticks around for 24 to 36 hours, looking for the activity to reoccur. The process is sort of like bringing reinforcements to a fight: you get your butt kicked once, but come back ready to rumble with more of your friends (in this case, stronger muscle tissues).
This is when you need to work out again. If the new cells do not experience activity, they will begin to atrophy (or break down) on a molecular level, to conserve energy. This is a survival mechanism left over from our hunter-gatherer days.
Once you’ve beat up on your muscles through training, your goal is to schedule your next training session at the peak of your body’s rebuilding phase. That point will vary by person, training experience, and whether you use proper recovery techniques. What are those? Glad you asked…

Proper Recovery Techniques 

Your workout recovery begins as soon as you wrap up your last set or catch your breath after your last sprint. The body acts quickly, so you need to act fast to ensure you get the best recovery possible.
Immediately upon finishing: Drink at least eight ounces of an energy drink or eat a few energy chews to help replenish the glycogen stores (your body’s main source of energy) depleted during activity.
Within the first half an hour: This is when your body is in an anabolic (muscle-building) state, doing everything it can to reinforce your tissues as quickly as possible—making it the prime time to help spur your recovery and strength-building. Fuel up (Post-Workout Meal Guidelines) with more carbs and fluids, and eat protein to help muscle regeneration. You can also:

• Take any supplements that you feel are appropriate. (Read about Recovery Supplements.)
• Ice down any problem areas.
• Do a cool down, appropriate to the session.

Up to two hours later: A few hours after your session, try a little stretching, paying close attention to the areas you worked the most. You’ll want to take it easy, holding deep stretches for 30 seconds at a time, which helps realign all the muscle fibers that have suffered micro-damage. Stretch opposing muscles in pairs (for example, quads then hamstrings), not in a random order. Towards the end of the two hours, eat another small meal with some carbs and protein.
Post two hours: Rest and relax. Take a nap if you can. Otherwise, just aim to get eight hours of shuteye in the evening. Proper sleep helps improve recovery even more.