That which doesn't kill me!
Working out with Intensity
The answer lies in a variety of factors and ultimately comes down to your genetic predisposition. Muscle density and dominant fiber type (fast / slow twitch) play a major role here. Unfortunately there is little you can do to change your makeup outside of having your brain removed and replaced in the body of some genetically altered beast (not a bad idea, where do I sign up?). The trick is to make the most of what you have and this is where intensity comes into play.
We have all seen the showman at the gym pile on the plates and then scream his guts out while he frantically squeezes out 2 to 3 reps. That's great, I do that sometimes my self. But what does he do for an encore? Never forget, we are bodybuilders, not powerlifters. Our goal isn't to be the strongest person in the gym, only the best built. With this understanding, our macho example here in only half way there. As difficult as he made his 2 to 3 reps appear, the truth is that it is nowhere near as difficult as it would have been if he had stripped a few plates and whipped out 20 to 25 reps. If you have never preformed an honest burnout set than then there are degrees of pain that you can't begin to comprehend. Bringing a heavy set to failure is not the same as performing a moderate weight set to failure. Not even close. By the time that the average lifter is racking the weight, a true burnout set has only begun. The next several reps (and I do mean several) are going to take every ounce of spit and venom that you can muster.
Disclaimer (you must be healthy to do this, if you have any health concerns whatsoever, resort to less drastic measures of shocking the muscles)
Here is an example of what I am talking about. Recently I had a fair amount of weight on the leg press. It was a weight that a few years ago would have been my one rep max. My goal for this set was a minimum of 15 reps. Fifteen reps came and I knew that I had something left. I could have racked it because I had reached my goal but I knew that if I truly wanted to exhaust my legs I had to go further. Eighteen reps and counting. People are beginning to notice. Twenty reps. The legs are burning but still capable of overcoming the resistance. Twenty three reps. It hurts, it hurts like hell. Everything in me is saying to rack it, rack it now. My face is beginning to look like a grossly distorted caricature of myself. An inflated balloon that is about to burst. But I'm not done yet. Hands off the supports and on the knees it's time for a little assistance. With help from above we are now at rep number 25. I'm hyperventilating. Seriously.
My quads are about to explode.
I hold the weight at full extension, take a few deep breaths and go for it. Rep number 26. Slowly. The weight reaches full depression and then slowly begins it final accent. Teeth gnashed in primitive furry. The weight resist like a 20 lb northern pike on a 5 lb test line. But this is one that isn't going to get away. I talk to the weights, commanding them, "YOU'RE MINE". And it is! Feverishly I reach for the pin to secure the final resting place. Head drenched in sweat and gasping for breath on the throne that I have conquered I suddenly realize, "I can't move my legs." Even so, I felt like I was in a house that was on fire and just had to get out of there and so I fell to the side. Lying on the floor like a beached whale, still struggling for air I reached for the closest weight machine and pulled myself upright. My chest was red and potted with petechiae (burst blood vessels). End of workout, I did what I wanted to do.
Ladies and Gentlemen, you have just experienced a true burnout set. This technique is used on occasion to shock the muscles. Over time our bodies become accustomed to the daily rigors of repeated workouts and thus anabolism slows to a snails pace. Therefore it is essential that we vary the program. Light days, heavy days. High reps, low reps. Heavy resistance alone will not penetrate the innermost depth of your muscle fiber. Also, honestly compare your pump and vascularity after a low rep and high rep set. No contest.
So what have we learned today?
The battle is not always to the strong but to him that endures.
Which brings up another axiom which I'm sure was originally intended for bodybuilders. That which does not kill me only serves to make me stronger.