In bodybuilding, assuming time under tension levels are equal, how does tempo affect muscle size and hypertrophy?
Thanks for this interesting question! It forced me to think a bit.
And I believe, with a little more work, I could probably expand my answer to fit all sorts of variables that can be played around with in our heroic muscle chasing quest fraught with risk and hazard. But I’ll try to keep it relatively short and sweet.
In the yin/yang cycle of lifting, the overriding principle of the circle’s first third is the concept of systematic application of stress. So in this sense, tempo is to hypertrophic response as weight is to reps and reps are to sets. In other words, it is one of the variables or tools with which you do the work required to get some muscles with.
Let’s unpack this seeming puzzlement by using an iron example.
When you do an exercise, say a preacher curl, one of the things that you deal with is internal muscular friction. When you are lifting the weight, the force of this muscular friction plus the force of gravity is working against you; when you are lowering the weight, only gravity is working against you. This is why studies show that you can handle less weight on the way up than on the way down. This point is important and will be useful in explaining the answer to your question.
Let’s decide that you are going to do a set of preacher curls with a 25kg. barbell for 1 minute. You have two options (you actually have many options, but we’re going to limit them for argument’s sake):
Option #1 (most common): 2 second upswing (concentric action) and 1 second downswing (eccentric action). So a complete rep takes 3 seconds and so you can fit 20 reps with this tempo into a minute.
Option #2 (a better choice to stimulate hypertrophy): 2 seconds spent lifting the weight up, 4 seconds lowering it. A complete rep takes 6 seconds in this case. You can now only fit 10 reps into that minute.
So, what’s going on here? In both cases the amount of work done by the muscle is the same. On the face of it, it also looks like Option #1 is generating morepower.
But here is where the concepts of muscular friction, application of stress over time and why the body builds muscles come in handy. When you are decreasing the tempo of your movement, you are taking advantage of the peculiar fact that your body can handle more weight during eccentric actions. This translates to applying more stress on or to the muscle, increasing the amount of disturbance to the body’s homeostasis and forcing the muscle to adapt to this threat by, guess what?
Voila! Bigger muscles.