Bill Starr on Sticking points

  Overtraining, as I’ve mentioned, is a major reason for many sticking points,
  but where that’s not a factor, weak areas are the culprits. In order to deal
  with them, you first have to identify them. Sometimes they’re rather obvious –
  perhaps weak adductors displaying themselves when your knees turn in during
  heavy pulls or squats, or a lack of trap strength on heavy cleans or snatches.
  Most are so subtle, however, that they need a trained coach to spot them, and
  not everyone has the opportunity to work out in front of such an individual.
  That means you have to find the weak area yourself. A tough task? Not at all.
  That is, if you have a power rack.

  You believe your form is correct in the back squat, and you work it
  diligently, making surer you’re not overdoing it. Even so, it’s been stuck at
  350 for more than six months, and you’re stymied as to how to get over the
  sticking point. The rack will reveal the weaker area right away.

  Set the pins in the rack a couple of inches below where you hit the bottom on
  the squat. While you can start this from the finish of the lift, most weak
  areas are either in the start or somewhere in the middle range, so it’s best
  to start from the deep bottom and work up. Squeeze under the bar loaded with
  135 pounds, and stand up with it. That will help you get the feel of what
  you’re trying to accomplish. Do only singles. Keep adding weight until you
  find your limit. Record that number, and mover the pins up to the middle part
  of the squat. Then repeat the procedure, and do the same for the finish. If
  you’re not positive where the weakest area is, you can do more than three
  positions, but usually three are enough.

  In this case it’s clearly the middle where you were able to use only 505.
  Reset the pins at that middle position, put 275 on the bar, and do three reps
  with that weight. If it’s not difficult, add weight and do another triple. Try
  to find a poundage that gives you three reps, and knock out five sets. It
  doesn’t matter what poundage you use in the beginning on partial squats
  because you’re going to be increasing it each time you do them. When you’re
  able to handle 30 or 40 more pounds than you used the first time around that
  weak area will be much stronger, and the new strength will display itself when
  you do the full movement.

  Another way to use the rack to strengthen a weak area is with either pure
  isometrics or isotonic-isometrics. I believe the latter is more effective as
  it’s often difficult to tell if you are, in fact, exerting 100 percent of your
  effort against the stationary bar. When you have weight on the bar and have to
  hold it against the top pins for a definite amount of time, you know for
  certain. That’s because if you slack off then, the bar will move away from the
  top pins.

  To work the weak middle very specifically, set the lower pins at the same
  place you had them for the partial squats. Then put two pins directly over the
  bar. The closer the better. You want to move the loaded barbell only an inch
  or two – no more than that unless the holes are set wide apart in your rack.
  You might have to stand on a board to place yourself a bit higher so the bar
  is closer to the top pins.

  Start out with a light weight so you can determine what you’re doing on the
  concentrated exercise. Squeeze under the bar, making sure your feet are
  positioned correctly and your torso is where it should be. Then elevate the
  bar up against the pins. Tap them, and lower the weight. Do that three times,
  and hold the third rep for a couple of seconds. Add weight and repeat. Now
  decide how much you can handle for your work set. It doesn’t have to be on the
  money the first time around, but it should be close. Tap the top pins twice
  with the bar and lock in the third rep, holding it for and eight-to-12-second
  count. Here the time element is more important than how much weight is on the
  bar. If you can’t lock into an isometric contraction for at least eight
  seconds, use less weight. If you can hold longer than a 12-second count, you
  need more weight. After a couple of workouts you’ll have a good idea of how
  much to use. Just do that one work set. Isotonic-isometrics are condensed
  strength work, and a little goes a long way.

  Of course, you can seek out weak spots in pulls and presses in the same way
  and make them stronger with isos. A learning curve is involved. When you lock
  the bar against the top pins, you must think about steadily increasing the
  pressure as the count gets higher. When you reach eight, you should be
  squatting, pulling or pressing with absolutely all your might. You should hold
  nothing back. Isotonic-isometric contractions strengthen the tendons and
  ligaments, which are the ultimate sources of strength. Be sure to warm up
  thoroughly before doing them. Locking into an iso hold on cold muscles is
  asking for a pulled muscle or attachment.