One of the best pieces of exercise advice is to make sure you know that your muscles grow when your resting not training. That's right, you don't actually get bigger and stronger when you're in the gym. It's what you do after your workout that's the real key to muscle growth. If you don't let your muscles recover correctly, you're body will become over trained and it will be in a state of constent "catch up". This is far from the ideal state that you want your body in. What you want is to truly prime your body for your next workout and give it enough rest and recuperation to fully optimize your training.
The worst thing you can do is over train your body. This will lead to muscle atrophy (breaking down muscle) and you may experience the flu because of this. When you train, make sure to limit your resistance training sessions to 45 minutes max. Your body's testosterone levels start decreasing after about 45 minutes, so anytime after this length and you're really just wasting your time. Focus on hitting it with a high level of intensity for 45 minutes and get out of there. Take care of business and start your recuperation. When you get back from your workout, you might also try sitting in a jacuzzi or sauna to really relax and let your muscles recover. Rest is extremely important when training hard, so make sure to take the time to recover and grow from your training sessions.
Kris Bierek is a fitness specialist for the health and fitness site http://www.ShapeFit.com where you can find FREE fitness tools like fitness newsletters, dieting tips, weight loss help, exercise questions and a free fitness analysis to help you get into the best shape of your life!