“Your muscles don’t know weight,” many bodybuilders say, almost waxing philosophic, “they only know tension, and that’s what stimulates growth.”
Well, in case you’re not familiar with this line of thinking, it’s been around the bodybuilding world for decades and what it refers to is the amount of time your muscles are working during a given set. If you perform one set of 8 reps and it takes 45 seconds, the time under tension is…you guessed it…45 seconds.
For a while this was just another theory. It didn’t go mainstream until a couple of flawed studies like this popped up with abstracts that made it sound like time under tension might play a vital role in muscle growth.
Suddenly, fitness gurus everywhere were sharing the “breakthrough” that the amount of weight you’re lifting is less important than the amount of time you keep your muscles under tension, and thus the “time under tension” school of thought was born.
Entire training methodologies were quick to follow that involved manipulating tempo to meet training goals and guys everywhere started incorporating “super-slow training” to reap the (apparent) benefits of increasing time under tension instead of weight lifted.
Well, like the many “weird little tricks” of the fitness space–you know, the ones that are supposed to increase your bench press or melt off belly fat–time under tension is not important enough to warrant special attention and is simply a byproduct of proper training that can, more or less, be ignored.
Let’s find out why.
What weight did you squat last week? How many reps did you get? What do you think would immediately happen to those numbers if you doubled your time under tension by slowing your reps down to half your current speed?
That’s right–the amount of reps that you could do with that weight would plummet. Depending on how slow you went, you might get half your normal reps or even less. And herein lies the big problem with emphasizing time under tension over load…
You see, the primary driver of muscle growth is progressive overload, and this means lifting heavier and heavier weights over time. If you want to build a big, strong physique, your number one goal in all of your weightlifting should be adding weight to the bar over time.
This is especially true for intermediate and advanced weightlifters who can no longer rely on their “newbie gains” to make progress.
Now, when you reduce the amount of reps you perform, you also reduce the total work performed by the muscle; and when you reduce the amount of work performed by a muscle, you reduce the muscle- and strength-building potential of the exercise.
The question, then, is if the “trade-off” of time under tension for total work is worth it. Does increasing time under tension “make up for” the reduction in work performed and result in more strength progression and muscle growth?
The research says no. For example…
These findings aren’t exactly surprising given the underlying mechanics of muscle growth and how intertwined it is with building strength (if you want bigger muscles, you’re going to have to get stronger).
It all comes back to progressive overload and work performed, and super-slow training just loses that battle. To quote researchers from Ithica College, who compared fast-tempo bench pressing to slow-tempo (my emphasis added):
“One-way repeated measures analysis of variance showed tempos with a fast eccentric phase (1 second), and no bottom rest produced significantly greater (p ≤ 0.05) PO [power output] and repetitions than tempos involving slower eccentric velocity (4 seconds) or greater bottom rest (4 seconds).
“This combination of greater repetitions and PO resulted in a greater volume of work. Varying interrepetition rest (1 or 4 seconds) did not significantly affect PO or repetitions.
“The results of this study support the use of fast eccentric speed and no bottom rest during acute performance testing to maximize PO and number of repetitions during a set of bench press.”
It’s also worth noting that back when I didn’t know what I was doing, I used to do a lot of slow sets to maximize time under tension and my results were in line with the research: I found it no more effective than my regular training routines, which were pretty crappy in reality.
The three variables that are going to impact your weightlifting results the most are frequency, intensity (the amount of weight you’re lifting), and volume (the amount of reps you’re performing in a given period of time).
If you get these things right:
…you’re going to make outstanding gains in the gym, regardless of whatever happens with your time under tension.