Recently WM, a personal trainer, e-mailed me with a question on the subject of time under tension and muscle growth.
“I read that the optimal time under tension for increasing strength and power is 4-20 seconds,” wrote WM.
“For gaining size it’s 40-60 seconds, and for endurance it’s at least 70 seconds. But what happens with the muscle between 21-39 seconds? And I’ve noticed that you don’t give any time under tension recommendations in Muscle Evo. Why not?”
How Does Time Under Tension Work?
When people talk about time under tension, they’re usually referring to the amount of time your muscles are working during a set.
For example, let’s say you do a dumbbell curl. It takes two seconds to lift the weight and two seconds to lower it. During each rep, your biceps are under tension for a total of four seconds.
Performing a set of 10 reps at the same speed would take a total of 40 seconds. Therefore, the total length of time your muscles are under tension during that set is 40 seconds.
If you slow down each rep so that it takes six seconds, it would take 60 seconds to complete a set of 10 reps. In which case, the time under tension is now 60 seconds.
Proponents of TUT-based training programs also like to prescribe a specific rep tempo, where you count the number of seconds it takes to lift and lower the weight, as well as the amount of time you pause at the top and bottom of the movement.
For example, a 4-1-2-1 tempo means taking 4 seconds to lower the weight, pausing for 1 second at the bottom, taking 2 seconds to lift the weight, and pausing again for 1 second at the top.
Why Timing Your Sets Is a Waste of Time
When I first read about time under tension in the late 1990’s, it seemed to make perfect sense.
And, being one of those people with a tendency to obsess over small (and often pointless) details, I invested a lot of time and effort in trying to follow the TUT guidelines as closely as possible.
I used a metronome to help me time the length of each rep. I read the books written by the “gurus” who promoted the idea. I secretly scoffed at the people using “antiquated” methods like sets and reps now that I had discovered “the secret” to packing on muscle.
All of which, for reasons I’m about to explain, was a complete waste of time.
Firstly, the length of time a muscle is under tension for during a set isn’t the only thing that counts when it comes to building muscle.
You also need to consider 1) the degree of tension and 2) the total amount of tension that muscle is exposed to during a workout.
“Mechanical tension is directly related to the magnitude of load or weight you’re lifting,” explains Brad Schoenfeld. “If you perform a rep at your 1 rep max (RM), it will necessarily create more mechanical tension than a rep performed at 50% 1RM.”
“Thus, sets of long durations will necessarily involve lower levels of tension than those of shorter durations, assuming training is carried out near or to momentary muscular failure.”
In other words, the muscle-building stimulus generated by a given workout depends not just on the length of each set, but the total number of sets you do, as well as the amount of weight you lift during those sets.
How Long Should I Be Under Tension to Build Muscle?
The standard advice is that to maximize strength, the ideal time under tension is about 20 seconds or less; to build muscle, it’s at least 40 seconds; and for muscle endurance, it’s at least 70 seconds.
However, there are plenty of studies out there to show that your muscles can be made to grow with heavy sets lasting less than 20 seconds or lighter sets lasting longer than 60 seconds.
In one trial, researchers got a group of guys to train their legs on the leg extension machine three times a week for 10 weeks .
In the first group, the time under tension for each set was 30-48 seconds. Group two, on the other hand, took between 90 and 120 seconds to perform each set.
Which group do you think built the most muscle?
Despite the big difference in time under tension, the amount of new muscle added to both legs was almost identical.
In other words, a time under tension that was deep in the endurance range stimulated just as much muscle growth as sets that straddled the strength and hypertrophy range.
Here’s another study to blow a hole in the theory that your sets need to last 40-60 seconds if you want to maximize growth.
Researchers from the University of Central Florida put a group of 33 resistance-trained men through eight weeks of strength training .
The subjects were divided into two groups:
Group one did four sets of 10-12 reps. Each rep took 3-4 seconds to complete, which means that each set lasted between 30 and 48 seconds.
Group two did the same exercises. They also did the same number of sets. But, they used a much heavier weight that limited them to 3-5 reps, which means that each set lasted between 9 and 20 seconds.
None of the differences in body composition between the groups were statistically different.
However, the researchers did find a clear trend towards greater gains in the group lifting heavier weights.
In other words, the men who trained using sets lasting less than 20 seconds were the ones that put on the most muscle.
How Long Should Each Rep Take?
In general, each rep should take around 3-4 seconds – 1-2 seconds to lift the weight, and another couple of seconds to lower it back down again.
However, the idea that you need to make a set last for a fixed amount of time has given some people the idea that slower lifting speeds work better for muscle growth — which they don’t.
For one, trying to make a set last longer is going to limit the amount of weight you can lift .
Let’s say that the best you can manage on the bench press is 200 pounds for a total of 10 repetitions.
If we assume it takes you a couple of seconds to lower the bar, and another second to lift it again, each rep will last a total of three seconds. Your set of 10 reps lasts roughly 30 seconds.
But at 30 seconds, your set is outside the 40-60 second range which is supposedly “optimal” for muscle growth.
So what do you do?
The obvious solution is to do each rep more slowly. Doubling the length of each rep so that it takes six seconds — three seconds on the way down and three seconds on the way up — should do the trick.
But there’s a problem.
Because you’ve slowed each rep down, you’re not going to be able to do as many reps. The only way you’re going to be able to do a set of 10 reps is by using a lighter weight.
So, you drop the weight by 25% to 150 pounds. Now you’re able to do 10 reps, using the slower speed of six seconds per rep. Your time under tension is now 60 seconds, which puts you right on the fast track to muscle growth.
Or does it?
It doesn’t, and here’s why.
Before, your training volume was 2000 pounds (10 reps x 200 pounds = 2000 pounds). Slowing your reps and reducing the weight means your training volume has dropped to 1500 pounds (10 reps x 150 pounds = 1500 pounds).
In other words, you’re now doing less work than you were before. And doing less work is a step in the wrong direction if you want to make your muscles bigger.
For a muscle to grow, the individual fibers that make up that muscle have to be both activated and stimulated for a sufficient length of time during a workout
However, performing reps at a fixed speed of four seconds per rep versus a self-selected speed has been shown to decrease both muscle activation and training volume .
More interesting still, increasing time under tension by slowing down your reps has not been shown to deliver superior gains in muscle size.
Researchers from the University of Sydney report that taking six seconds to do a dumbbell curl is no more effective for muscle growth than a rep lasting two seconds .
After six weeks of training, there was no evidence that one rep speed was better than the other for increasing arm size. In fact, strength gains were roughly 10% greater with the faster lifting speed.
It was much the same story when a team of Japanese scientists compared slow and fast lifting speeds . Reps lasting six seconds didn’t work any better than reps lasting three seconds for increasing whole-body muscle thickness or maximal strength.
A follow-up study, which involved squatting twice a week for six weeks, also shows no benefit to slowing down the eccentric, or lowering phase, of a rep .
Subjects taking two seconds to lift the weight and four seconds to lower it didn’t grow any faster than lifters who lowered the weight in two seconds.
What’s more, it was the faster group who gained the most strength. They finished the study squatting 18 pounds (8 kilograms) more than the four-second group, despite the fact that both groups started out in roughly the same place.
In short, as long as you’re lifting and lowering the weight under control, rather than letting the weight control you, there’s very little point in trying to make a set last for a specific amount of time.
Why Is Time Under Tension Important?
You will no doubt come across many articles saying that time under tension is “important” when it comes to muscle growth. Which of course it is.
However, simply saying that TUT is “important” doesn’t mean much because your muscles are under tension for a given amount of time during ANY type of resistance training.
And changing the speed at which you perform each repetition is far from being the only way to alter TUT. If you focus only on making a single repetition last longer, you’re ignoring several other ways of exposing your muscles to a growth-producing stimulus.
Think about it.
When you do more sets of a given exercise, you’ve increased time under tension. Do more reps and you’ve increased time under tension. Train a muscle group more frequently and you’ve increased time under tension.
So, it’s a pretty safe bet to say that manipulating time under tension is going to have an effect on your results one way or another.
Chisel Away at The Inessentials
Rather than complicating your workouts with stopwatches, metronomes and whatever else, I’d suggest that you take the advice of legendary martial artist Bruce Lee and make them as simple as possible.
Bruce was a big fan of keeping things simple. In fact, he once said that the art of jeet kune do, the martial art he founded, was “simply to simplify.”
“In building a statue,” Lee said “a sculptor doesn’t keep adding clay to his subject. Actually, he keeps chiseling away at the inessentials until the truth is revealed without obstructions.”
“Jeet kune do doesn’t mean adding more. It means to minimize. In other words to back away from the inessentials. It is not a daily increase but a daily decrease.”
Measuring TUT is one of those “inessentials” that you can easily forget about and still get great results.
Or to put it another way, if your training program is set up properly, TUT isn’t a variable that you need to spend any time measuring or even thinking about.
The way that some people talk about TUT, you’d think it was an indisputable fact that’s been verified in numerous well-controlled studies.
However, I’ve seen nothing to convince me that basing your workouts on TUT guidelines works any better than using conventional loading parameters like sets and reps.
The numbers are based on the opinion of a few people and have been blindly accepted as “the truth” by a lot of people who should know better.
The length of time that a muscle is under tension for during a set is a lot less important than the total amount of tension it’s exposed to during a workout, the degree of tension, as well as how often that tension is applied over the course of a week.
A lot of guys go to the gym, train hard, and get bigger and stronger without paying the slightest bit of attention to time under tension. I’d highly recommend that you do the same.
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ABOUT THE AUTHORChristian Finn is the nation’s leading authority on science-based, joint-friendly ways to build muscle. A former "trainer to the trainers," he holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.