TempoRep tempo · Lifting tempo
The speed of each phase of a rep, often written as four digits such as 3-1-1-0.
Rep tempo is the speed of each phase of a repetition, often written as four digits such as 3-1-1-0: three seconds lowering, one second paused at the bottom, one second lifting, no pause at the top. Some notations write the lifting phase as X to mean as fast as possible.
Its useful function is preventing the rep from collapsing. Dropping the weight rather than controlling the descent removes a meaningful part of the stimulus, and a prescribed tempo is a simple way of making a lifter stop cheating the lowering phase.
It is also a way of standardising a set so that progress means something. Adding weight while gradually speeding up and shortening the range is a common way of appearing to progress without doing so, and a fixed tempo makes that harder.
What it is not is a lever to maximise. Very slow tempos reduce the load you can use and the total work you can do, and studies manipulating tempo generally find equal or worse hypertrophy compared with a normal controlled speed. Longer is not better.
Pauses have specific uses. A pause at the bottom removes the stretch reflex, which increases difficulty at the hardest position and is useful for building strength out of the hole in a squat or off the chest in a bench press.
Lifting with intent, meaning trying to move the bar quickly even when it moves slowly, is well supported for strength and power, which is why the concentric is usually the phase left unrestricted.
In practice, control the lowering over roughly one to three seconds, lift with intent, add pauses deliberately where you are weak, and stop counting beyond that.