I was wondering if someone could tell me, in regards to tempo, when you are performing a pressing movement with the chest (ie benchpress), does the isometric contraction occur when the bar/dumbells are level with the chest or does it occur just short of lockout?
an isometric contraction is one in which the muscle does not move, so if you pause at the bottom of a bench press and just hold the weight there, it is a submaximal isometric contraction. There is also one at the top of the bench press, when you are just holding the weight up there.
Just short of lockout or at your strongest point.
It's at the bottom of the movement, you don't neccesarily have to pause to get the isometric contraction. What happens is the bar movement at some point in time/movement must come to a complete stop in order to reverse the motion so you can begin to press the bar up. It's at the change over point that you have the isometric pause. You could hold the position for longer to increase stress, but I think if you do an isometric squeeze at the top, make sure that your arms are not locked out, so you can apply tension to the muscles being utilized.
Set up in the power cage and set the pins at your weak point of the lift. If you are weakest at the bottom third set up there if you weaker just before lockout set up there. Then do the half or quarter reps for 5 reps. On the 5th rep push up against the pins as hard as possible. Do this for a 8 second hold then try to do a 6th rep. If you can do the 6th rep, increase the weight next set. The reason for this is that isometric contractions will only increase strength from about 20 degrees up and down. So if you are at the bottom half of the lift the only strength increase will be about 1 or 2 inches upward and downward. This is something that many powerliftier do to increase their strength at the there weak spot. Hope that helps.