This muscle-building technique is simple: During the same set you alternate between very slow reps and fast reps – the fastest you can do with perfect form.
Specifically, you do 2 reps with a 5 second up and 5 second down tempo followed by 2 fast reps. This is referred to as one "cycle." Each set has either 8 or 12 reps (two or three cycles of four reps), or between 8 and 12 reps if you hit failure before completing 3 full cycles. Here's what it looks like:
Log Press: Tempo Contrast Method
This method recruits more muscle fibers due to the different types of rep contractions. Additionally, alternating between slow reps and fast reps allows for the momentary "capturing" of waste products inside the muscles, which leads to the release of growth factors that stimulate protein synthesis and muscle growth. The accumulation of metabolites, as well as trapped blood inside the muscle, leads to an excruciating pump.
Other Muscle Groups & Exercises
It's not just for overhead pressing. This method works especially well for biceps, quads (leg extensions, leg press), hamstrings (leg curls), and chest (cable cross-overs, pec deck, flyes), as well as for pressing exercises like bench press.