We will use the quadriceps as our example here. These principles can be applied to the other major bodyparts. Or can they? That's something for you to look into on your own.
By now we all realize that the squat has its worth in bodybuilding. And we also recognize that performing squats and only squats is not the quickest or most effective way to develop the quadriceps. That being said . . .
Consider the squat variations. Here we're talking about any form of squat with the bar held on the back. I'm sure, again by now, that you've already looked into and experimented with the numerous styles of squatting, beyond simply "high bar" and "power" squats. There's a lot! If not, do that for a year or three and record your results. That should cover it, for starters.
Okay then. As long as you're moving the bar (in any exercise) at your absolute maximum rate of speed, then power is being displayed. But, for our purposes it's important to determine -- at what load/speed is power developed most effectively?
For every lifter and for each of his exercises there is a point at which power (remember that definition?), is maximized. Below that point maximum power cannot be generated because the weight is too light. Power cannot be developed with an empty bar, of course. The load/speed at which power is developed most effectively is neither with such light weights, since gravitational limits on movement speed prohibit a compensatory response to the light load, nor with the heaviest possible weights, because movement speed is too slow and the low number of reps per set does not permit maximum adaptation for bodybuilding.
Note: There is a compensatory response in the body even to the illusion of a heavy weight. Very interesting stuff here. Blindfold yourself and have someone load a bar for you, so that you have no idea how much weight is on it. Now lift it. Very interesting stuff there.
When training to develop power for bodybuilding, 5 sets of 5 is a good starting point. These figures can be modified according to your progress, but they should never go below 4 reps or rise above 7 reps. The number of sets you can do before fatigue limits your ability to handle the target weight appropriately when training to develop power is your guide to determining the number of maximally beneficial sets. Look at it this way . . . using the pump to gauge if you can continue working a specific bodypart is very similar to this, this using bar speed to determine if you've done enough power development training for the day. If the bar speed is sluggish, you're through for now.
As long as you're in those rep ranges mentioned, and you are are moving the bar explosively on the 'lift' portion, it'll work out fine. Now, don't get all silly and simply try to move the bar as fast as possible in both directions. You're still controlling the weights and feeling the muscles work. Stretch. And Squeeze. Remember?
This is bodybuilding, not powerlifting and not weightlifting.
Sure, bodybuilding! So why bother with any of this "non-bodybuilding" nonsense?
Well, this explosive style of training will improve your ability to RECRUIT a maximum number of muscle fibers, which is exactly what you're after when you CONCENTRATE on the muscle you're working.
Why periodically spend precious training time training to develop explosive power?
Because explosive training will improve the quality of the overload you're putting on the muscle.
Unfortunately isolation exercises, by their nature, don't allow you to use enough weight safely to train for explosive power. For example, the leg extension. The intensity (percent of max) needed to develop power requires a higher-than-safe load to be used. Leg curls reflect the same problem.
The obvious compromise - the leg exercise that proportionately balances the isolation factor and intensity requirements -- is the squat with the bar high on the neck and the torso maintained in an erect position. Both isolation and intensity are held at high enough levels to be maximally effective in developing explosive leg power for bodybuilding purposes.
But you have to remember to EXPLODE from the hole. Lower slowly and under full muscle control with total concentration, then explode up.
This form of squat is infinitely better for bodybuilding purposes than powerlifting squats for several reasons:
1) Powerlifting squats are designed to spread the task of moving the weight over four muscle groups, thereby overlooking the isolation principle altogether.
2) High bar, erect squats, on the other hand, do not (when done in a manner appropriate to what we're trying to achieve here) significantly involve the glutes, hamstrings or erector spinae, as do powerlifting squats, but rather centralize the effort in the quadriceps.
3) The glutes, hamstrings, and erectors are better isolated for bodybuilding purposes with other exercises.
4) High bar, erect squats are less traumatic to the vertebrae than are powerlifting squats, because the vertebral column is perpendicular to the floor, and the force is compressing rather than shearing upon the spine. Also, high bar, erect squats are safer because less weight is used than with power squats.
Of course, as a bodybuilder you're after leg development, so the choice is simple. Don't be confused, don't keep thinking what's good for the powerlifter is good for the bodybuilder.
Certainly, many of the methods of powerlifting can, with alterations, be fitted to bodybuilding advantage, just as many of the methods of bodybuilding can be tailored to proper use in powerlifting.
Just be sure you know what you are seeking at all times.
Your whole life can become much clearer over time once you determine that.
The man of advanced perceptual development seeks the results of what superficial level results he achieves through his dedications on the physical plane, and sees all these desires and the resulting modifications as a totality and not a childish triad of mind/body/spirit. The burning, the bush, and his perception of the burning bush are One.
Go figure, eh.