When it comes to building muscle the formula for success is simple. You select a weight, lift it a certain number of times, put it down, rest, then lift again. The lifting weights' part is crucial of course, but the period of time that you rest between sets can also have a dramatic impact on the effectiveness of your training session. In fact, rest is a training variable as important as sets, reps, weight and tempo in ensuring you hit your fitness target.
That's because the amount of rest between sets can influence the efficiency, safety and ultimate effectiveness of any given strength-training program, so it becomes crucial to keep in rhythm with the periodization of your workouts. Because when you lift weights, you do so to push your muscles out of their comfort zone because it's this stress that makes them stronger. But there is only so much work they can do before their energy stores become depleted, hampering their ability to perform additional reps with good form. By resting for a predetermined period you give your body time to resupply the muscle cells with fuel so they can do more lifting.