This was a line in a song I used to listen to, but I have found that it can apply to training also. Last week friday I decided to go against everything that was going on at the time and make it a heavy squat day. I should have known what was going to happen next. I lifted heavy although I only slept 4 hours the night before, performed a short warm-up, all the weights feeling heavy, and lifting heavy for 4 weeks straight. I guess I do not have to tell everyone that on my third heavy set I strained my lower back. Needless to say, I took this week off.
Summary of my points
* Listen to your body to decide when to take a break
* Make sure you properly warm-up
* Pay close attention to your exercise form
* Don't lift heavy all the time
* Be sure to get adequate sleep
* Eat a snack with a decent amount of protein & carbs to sustain your energy level