Pause in the Contracted Position
When Ian King refined the three number tempo system (which was ultimately popularized by Poliquin), he left out the pause in the contracted position for purposes of simplicity. However, I think bodybuilders are familiar enough with tempo prescriptions that it's time to introduce how important this variable can be.
The pause in the contracted position has very different effects on different exercises. For example, taking a pause at the top of the bench press (when your arms are fully extended) and taking a pause at the top of a chin-up (when your head is over the bar) are very different. In the bench press, the fully contracted position is the "easiest" portion of the lift. In a chin-up, however, holding your head over the bar can be pretty damn hard.
We also need to distinguish between different types of pauses. Try this, stop reading right now and do four reps of "chair dips" wherever you happen to be sitting, just like you would do bench dips in the gym. Onthe first two reps, I want you to extend your arms to their full lockout position, noting how much tension is reduced at the top of the movement when your arms are locked out. The next two reps, stop just short of lockout, noting how much tension increases at the top of the movement. With pulling movements there really are no differences, but with all presses, triceps exercises, and squatting movements, this difference in top-position pauses will become a factor.
This pause can have very different effects depending on the style you use. In the bench press, for example, extending to full lockout and pausing there for a second will improve your strength during the next rep due to the small amount of rest you'll get during the pause. On the other hand, extending to just short of lockout will cause a greater degree of fatigue and decrease your strength during the next rep.
So what kind of pause should you use? Both of them! Just like everything else in the iron game, there's a time and a place for both types. What's important is how you plan the variations.
In maximal strength training, it may be advantageous to take a brief one second pause in the full lockout position in exercises like the bench presses, military presses, dips, squats, etc... Taking this small break in the set can help you sustain your power output for more repetitions.
However, taking this pause decreases muscle tension, which is not what we're looking for in a hypertrophy program. So in a hypertrophy phase, the pause should be taken just short of the lockout position to maximize tension on the muscle. It would also be smart to pause in pulling exercises like chin-ups, rows, and pulldowns. In these exercises, the contracted position is the point at which the muscle has maximum tension.
Most of the time, I prescribe a pause at the top of any row, chin, or pulldown, even in maximal strength training. In these movements, the "rest" period is at the bottom in the stretched position, so a longer pause should be taken there instead of the contracted position.