One muscle-building strategy is a concept known as time under tension. The idea is that the longer you can keep tension in your muscles during a set, the more you’ll exhaust them, forcing them to grow to adapt.
One way to increase TUT is by doing more reps (duh). The other is to pause an exercise at a point in its range of motion and hold it for time. With countdown sets, you accomplish both simultaneously, delivering the maximum stimulus.
How it works
The problem with doing high reps (12 or more, typically) is that your form tends to break down, increasing your risk of injury. It also forces you to use lighter weights, sacrificing muscular tension. With countdown sets, you can fatigue your muscles while keeping your reps low by interspersing isometric holds (pausing a movement), effectively creating a long-lasting, high-TUT set.
For instance, you could perform six lateral raises and then hold your arms at 90° for six seconds, then repeat, dropping the reps and holds to five, four, and so on down to one.
Try this program for six weeks and you’ll see how more tension in your life can actually be a good thing.
Perform each workout (Days I, II, and III) once per week, resting a day between each session. Perform exercises marked with a letter (A, B, and sometimes C, or even D) in sequence, resting as needed in-between. So you’ll do a set of A, rest, then B, rest again, and repeat until all the prescribed sets are done. Perform the remaining exercises as straight sets.