I have found that most athletes and clients have the mindset of "more is better" when it comes to training. I suppose this is not unusual considering the culture in which we live, but if you live by this philosophy in terms of your training, you will never be able to guide your training to where it needs to go.
There is an inverse relationship between volume and intensity. Intensity, in programming, means the percentage of your maximum strength. Volume is the total amount of weight you use during a workout, a week, a month, a program, etc. If I were to bench 350 pounds, that would be pretty damn close to my current maximum. However, I might get only two cracks at it—for a volume of 700 pounds. But why would I only be able to get two to three chances with it? Because lifting with maximal intensity is more central nervous system intensive. In fact, thanks to Louie, we know that lifting at or above 90% of your one-rep maximum strength for more than three weeks at a time (with the same exercise) will actually max-out your central nervous system, and it will start to regress.
Compare this to bodybuilding training—you might be working on your chest one day (universally Mondays) and have a total volume of 8,000 pounds (for that workout) for __weight x __reps x __sets. You can handle a lot more volume because you aren’t working anywhere near your maximum strength.
Still, for one reason or another, this example usually doesn’t hit home for many people. So, to offer a different view, think of box jumps.
If I told you to jump on a 12-inch box 100 times during your workout (although I would never do this), you would be able to do it without thinking too much about it and with relative ease both physically and mentally. It would not be very CNS intensive. However, if I told you to jump up on a 36-inch box even 30 times (again, not happening), you would have to put a tremendous amount of mental and physical exertion into it, especially as you completed more and more reps. It's hard to mentally think about doing this, and I can guarantee that most people would fail.
As you can gather, the boxes represent the weights used in the above example. The higher box represents working at your near-maximal strength output and the lower box represents much less of a percent of your maximum strength, akin to bodybuilding/high volume training.
Thus, more is not better—optimal is better.
Hopefully theses examples have helped you understand this concept, and the next time you want to try and continue to get one-rep maxes during you training, just think about the box...and of trying to jump with near-maximal effort and height over and over. Again, it ain’t happening.