How to Manipulate a Rep's Pace to Build Muscle
A common thing I notice in the gym is people ignoring the pace at which they are doing their reps and sets. Pace is just as important as reps and sets when it comes to building the perfect muscle-building workout. Before I talk about pacing, I just want to give you my explanation. Tempo is the speed at which you raise and lower the weight, the pauses at the top and bottom of each rep, and the total time of the set. Next I want to tell you how to read tempi, since they are usually written with just numbers on one line...

How to Manipulate a Rep's Pace to Build Muscle
A common thing I notice in the gym is people ignoring the pace at which they are doing their reps and sets. Pace is just as important as reps and sets when it comes to building the perfect muscle-building workout. Before I talk about pacing, I just want to give you my explanation. Tempo is the speed at which you raise and lower the weight, the pauses at the top and bottom of each rep, and the total time of the set. Next I want to tell you how to read tempos, since they are usually written with just numbers on one line. An example of a posted tempo would be 4242. This means that you increase the weight for four seconds, pause for two seconds at the top of the rep, lower it for four seconds, and finally pause for two seconds before moving on to the next rep.
Some people write them out with just three numbers like 313 and ignore the pause at the bottom. I prefer the pauses because they stop the momentum, and just swinging the weight up and down takes a lot of stress off the muscle. Another thing to note is if the tempo contains an “X”. All that means is to explode on the way up as quickly as possible. Seems simple enough, so let's dive into common tempo manipulations. One thing to note very quickly. Some people write tempos the other way around like I do. Some have the eccentric or lower the weight part first. Just be aware, because there is no universal law to writing tempos.
Fast tempos
Fast tempos are not typically used to build muscle because they do not keep the muscle under tension long enough. Instead, they are great for explosive training. A typical explosive training pace would look like X0X0, or what I call the hug and kiss pace. Explosive training is just a quick movement designed to mirror normal sports to allow athletes to gain strength, access it and use it quickly. Typically, explosive training is not done with too many dumbbells and barbells, but you mainly use bodyweight exercises and medicine ball exercises. Medicine balls are great for explosive training because you can throw the ball and perform movements that aren't possible with a dumbbell. Bodyweight exercises are easy to manipulate for explosive training because they allow you to lift yourself off the ground. Push-ups, where you push yourself away from the ground as hard as you can so you're airborne, and jumping squats are good examples of explosive bodyweight training.
Slow pace
To be honest I don't see much value in really slow tempos, and by slow I mean more than 15 seconds per rep, so the tempo would be 6262.
Muscle building tempos
Now to the bread and butter of manipulating the tempo. If you want to do this for muscle gains, you probably already know that you should use 8-12 reps. At least that's common knowledge, but to add even more detail to your muscle building training plan, you should use tempos that can keep the muscle under tension for 40-60 seconds. Anything below that will come out with strength gains, and anything over 80 seconds will come out with aerobic gains. The best is between 40-60 seconds. To get our time between these recommendations we need to do about 5-6 seconds per rep. So my recommended tempo would be 1131, 1121 or even 1221. Any of these tempos are great because for 8 reps the seconds are around 40-48 seconds and for 12 reps they are 60-72 seconds.
Inspired by Greg E Cook