Isometric exercise or isometrics are a type of strength training in which the joint angle and muscle length do not change during contraction (compared to concentric or eccentric contractions, called dynamic/isotonic movements). Use isometric contractions to increase 'neural drive.'
Isometrics are a great way to increase neural drive as they increase motor unit activation at the angle at which you are isometrically contracting. Holding an angle against resistance is known as an isometric contraction. We often use this type of contraction if we find there is a sticking point in a movement pattern. An added benefit to isometrically contracting different points in a movement pattern, is that you increase strength +10 and -10 degrees of that which you are isometrically contracting.
This means you are increasing neural capacity and overall strength through a pattern of movement, especially if this is done throughout a pattern over a periodic time frame. This type of loading is used a lot by power lifters who have sticking points in there lifts and who's goals are to lift heavier. It is also commonly used in rehab to strengthen tendons and re-establish neural connection between mind and under active muscles. Personally I use isometrics in pulling exercises or around the mid point of a press. I especially use it with pulling on the general population at the top end of the contraction.So for example on a seated row I'd get my client to hold the row at there chest for a count of 1,2 or 3 seconds depending on the training effect and extent of the emphasis I'd like to place upon them.
Most people are very weak in this position so the use of the isometrics can help speed up the strength gains needed. For the press the mid point of the lift is more than likely a sticking point for the majority. Using a isometic hold around this range can help overcome this problem over a periodic time frame and help you develop a heavier overall pressing movement.
Next time you develop your training program use some isometrics and watch your strength shoot up:D