Written by Garett Reid | NSCA, CSCS, CISSN, M.S.E.S.S
Fact checked by Kiel DiGiovanni, Co-founder
FACT CHECKED
Have you ever seen a guy doing bicep curls at a speed of 100 RPM as if he's racing to do 100 reps as fast as possible? Have you thought that he should slow down to work his muscles better? Well, that's basically the premise of time under tension.
Time under tension, or TUT, has made some big waves in the fitness industry over the past couple of decades, and its effect is still felt in some bodybuilding circles. The basic premise is that to maximize muscle growth, you should extend the amount of time the muscle is contracting by slowing down your rep.
As we know, a muscle doing more work will effectively result in more muscle growth. Therefore, increasing the time a muscle is under tension would cause greater growth. However, muscle growth isn't as straightforward as this, and many variables must be considered. We will look at what research says about time under tension and whether it should be a factor to worry about when training.
What Is Time Under Tension?
Imagine if you had to carry 100 lbs of cement from the hardware store all the way to the parking lot because all the trolleys were busted. Would you do that by walking slowly, or would you try to move as fast as possible? Obviously, you're going to go as fast as possible, as the longer you hold onto the weight, the harder it gets! When a muscle works more, it becomes more and more fatigued!
Time Under Tension (TUT) simply refers to the active time in which tension is placed on a muscle during an exercise and demands a contraction. As a result, a muscle with a longer TUT will experience higher intensity even if you're using the same weight.
More importantly, TUT is an adjustable variable that lifters can use to increase the total work a muscle performs. Placing tension on a muscle is one of the most essential variables that promotes muscle growth, with some claiming it is the primary driver of muscle growth.
Regardless of its exact place on the muscle gains hierarchy, we know it is an essential component. As a result, lifters began to theorize that they could simply perform a rep slower to increase tension and ultimately gain more muscle.
TUT And Tempo Training
As you could probably guess, this is closely related to tempo training, a style of training that emphasizes using different lengths of time to perform the different contractions or parts of a movement.
Whenever we perform a rep with any exercise, there are four sections a muscle overcome;
- Eccentric (Going down)
- Bottom (Transition from eccentric to concentric)
- Concentric (Going up)
- Top (Transition from concentric to eccentric)
While TUT refers to the total time it takes to perform these four parts, tempo training prescribes a specific and oftentimes different duration for each of the four parts. For example, let's pretend you're prescribed a tempo of 3/1/3/1. This would translate to performing the parts with the following duration;
- Eccentric - 3 seconds
- Bottom - 1 second
- Concentric- 3 seconds
- Top - 1 second
In regards to time under tension, this would mean that each rep took 8 seconds. So, if you did 5 reps, the total time under tension would be 40 seconds. However, you could also perform a repetition using 4/1/2/1. This would mean a longer eccentric and a shorter concentric. Even though the total TUT is still 8 seconds per contraction, as we'll see later, this could make a big difference.
How Long Should Your Time Under Tension Be?
It depends on who you ask. While there have been quite a few studies on TUT, there's still no specific time you should aim for. One frequently repeated number is 50-70 seconds, taken from legendary strength coach Charles Poliquin. However, this number comes from gym observation rather than research.
This leads to a massive issue with solely relying on TUT to enhance muscle growth. Even taking this number, 50-70 seconds, leaves quite an extensive range. If someone were only to use 50 seconds, that would only be 70% of the work performed by someone who used 70 seconds.
That little thought experiment should be enough to illustrate that time under tension probably shouldn't be the primary variable to consider.
Is There Evidence For Time Under Tension?
Just like Charles Poliquin's suggested time, it seems that most of the evidence supporting time under tension training comes from a mixture of theory and anecdotal sources. On the other hand, more than a few studies suggest it's not that important.
Evidence For Time Under Tension
One piece of scientific research that is often used to support TUT training comes from 2012.¹ It had two groups of men perform knee extensions using 30% of their 1RM.
- One group: Concentric & eccentric contractions of 6 secs each
- One group: Contractions of just 1 second
At the end of the sessions, muscle protein synthesis rates were significantly higher in the 6-second contraction group.
That sounds great, but there are a few issues. The primary one is that the lifters were only using a weight of 30% 1RM, which is not how lifting works in the real world.
If a lifter used a weight this light, it would make sense. Slowing down the contraction would have a larger effect than performing fast simply because it's not heavy enough to challenge the muscle fibers. This is why loads of 70% or greater are generally recommended for muscle growth.
Now, using light weights with long TUT could be an interesting tactic for several groups of people:
- Those in rehab
- Trainees with limited equipment
- The elderly
These populations could get better results without needing to use heavier weights. However, this study doesn't really support the use of healthy lifters.
Just because you can doesn't mean you should.
Evidence Against Time Under Tension
On the other hand, multiple studies suggest that TUT provides no intrinsic benefit when all variables are considered.
For example, one study investigates early-phase muscular adaptations in 34 untrained women subjected to slow-speed (SS), traditional-strength (TS), traditional-endurance (TE), and control (C) resistance training regimens over 6 weeks had two groups of women perform leg extensions using different TUT durations.²
Slow group:
- 40-60% of their 1RM for 6-10 reps
- 10-second concentric | 4-second eccentric.
Traditional group:
- 80-85% of their 1RM for 6-10 reps
- 1-2 seconds concentric and eccentric
Results after 6 weeks:
Traditional group:
- 33% increase in their type IIa muscle fibers
- 37% increase in their type IIx
Slow group:
- 12% increase in their type IIa muscle fibers
- 17% increase in their type IIx
It's important to note that this study occurred in untrained lifters. Untrained lifters are the most sensitive to training, meaning they see muscle growth more "easily." However, there was a considerable difference in results in this study, suggesting that TUT would be even less effective in trained lifters under the same circumstances.
Now, we could report on many other studies, but the result is more or less the same. The main takeaway is that time under tension is simply one variable of muscle hypertrophy, and a wide range of TUT can be used effectively in conjunction with others, such as load and overall volume.
In fact, a large meta-analysis suggests that a person can see similar gains in muscle growth using a total repetition duration of anywhere from 0.5 to 8 seconds when all other variables are accounted for.³
This is because it seems that training to failure is ultimately the primary goal. So, while you could do this using a very slow rep, you can also do it with a faster rep.
Faster Reps For Muscle Growth?
This one may surprise you, but there is evidence that supports a faster concentric contraction for muscle growth!
A 2009 study demonstrated that lifters using a one-second concentric contraction saw greater biceps growth than those who used three seconds!⁴ Obviously, faster repetition is going to decrease TUT, which is in direct contradiction with slow reps, which is what's usually promoted!
Remember, similar results were seen in the study above with untrained women. The theory behind why this may occur is that performing the concentric contraction as fast as possible requires the higher recruitment of type II muscle fibers.
However, it's important to note that this applies explicitly to the concentric contraction. Things change when performing the eccentric contraction.
Learn more about performing faster reps with our post Velocity Based Training for maximal strength gains.
What is Slow Eccentric Training?
Eccentric training is a style of resistance training in which a lifter uses prolonged "time under tension" solely on the eccentric contraction.
Why would this matter? Through extensive research, sports scientists have discovered that eccentric contraction plays a significant role in muscle hypertrophy and strength gains. When measuring the force output of eccentric contraction and concentric contraction, the eccentric produces significantly more force.
Think about your max bench press; let's pretend it's 225lb. Now imagine you put 230lb on the bar. Once that bar gets to your chest, it's likely stuck there. However, you could relatively easily hold it at the top and then lower it down to your chest in a controlled manner.
In addition to this more excellent force production, the eccentric plays a more significant role in muscle hypertrophy. In theory, this means that if lifter A only performed the eccentric contraction, and another lifter B only performed the concentric contraction, lifter A would see more significant growth.
Just as fast concentric contractions produce greater hypertrophy, the opposite is true for eccentric contraction, and slowing down may result in more muscle growth.
Want to know more about the different parts of an exercise? Check out our post that goes depth about Concentric vs Eccentric Muscle Contraction.
Things To Consider With Time Under Tension Training
The entire premise of time under tension training is that you should lengthen the time the muscle is contracting to increase muscle or size. But here's the thing: your rep speed will always slow down as you approach failure.
At the same time, while you may perform a rep for a longer duration, this will ultimately lead to fewer reps.
Pretend you perform an exercise with a 4/0/4/0 tempo and then perform the same exercise with a 1/0/1/0 tempo. If you perform both to failure, you will perform significantly more reps using the 1/0/1/0 tempo.
Note the word failure used just now. This seems to be the key in training; so long as you train to failure and perform reps with control, the exact speed won't play much of a role.
Time Under Tension Is Just Another Training Variable
People who obsess over time under tension behave as if it is the only variable that affects muscle growth. It's not. Muscle hypertrophy is a much more complicated process and relies on numerous physiological processes that can be affected by numerous variables.
The only time that increasing time under tension would likely be the deciding variable is when all other variables are equal.
For example, let's pretend a person performed bicep barbell curls using a 3 X 8 rep scheme with 70% 1RM and a fast tempo of 1/0/1/0. Then, another person performed bicep curls with 70% 1RM but used a slow tempo of 5/0/5/0. In this situation, the slower tempo would likely see more significant growth. Maybe.
However, you could use more weight or perform more reps with a faster rep speed. This would likely even things out.
Applying Time Under Tension To Your Training
While time under tension is essential to applying mechanical stress to the muscle, the evidence to support the general recommendation of simply increasing TUT is flimsy. However, there is one piece of advice that you can apply to your training to maximize adaptations.
Quick Concentric, Slow Eccentric.
As we have alluded to above, while randomly increasing TUT seems fruitless, some studies suggest that using tempo training to alter the speed of the concentric and eccentric may increase adaptations.
In 2021, a large review examined all available research on tempo speed and adaptations.⁵ Here's what they found:
"The results of studies indicate that neither isolated slow nor isolated fast movement tempos are more or less effective for muscle hypertrophy, but it seems that the most favorable is a combination of slower movement in the eccentric phase with a faster movement during the concentric phase."
Note that even here, researchers still offer the general recommendations of "fast" for concentric contractions and "slow" for eccentric contractions. Why? Likely because of all the variables we spoke about above that also play a role in muscle growth. However, we do have some info to provide some guidelines.
When performing the concentric, instead of trying to use a specific time, you should be more concerned with your intensity; perform the concentric with maximal or near maximal effort. Again, the idea is to demand more power, which will require more muscle activation.
In terms of the eccentric contraction, a slow and controlled three seconds is likely a good starting number.
Bottom Line For Time Under Tension
Yet again, we find another training method that has been elevated to a higher level and made more important than it is. To be clear, time under tension is very important, as this makes our muscles grow. However, building your entire routine around it is likely a waste of effort.
In reality, it's simply one variable that can affect muscle growth and likely doesn't need much thought in its manipulation. If you are using an appropriate load and are training to near failure, the time under tension will take care of itself. Concerning a specific tempo, it seems that a general recommendation of a "slow eccentric, fast concentric" is about as complicated as it needs to get.
Learn about more training techniques with our post High Reps vs Low Reps: Which Is Better?
References
- Burd, Nicholas A., et al. “Muscle Time under Tension during Resistance Exercise Stimulates Differential Muscle Protein Sub-Fractional Synthetic Responses in Men.” The Journal of Physiology, vol. 590, no. 2, 15 Jan. 2012, pp. 351–362, https://doi.org/10.1113/jphysiol.2011.221200.
- Schuenke, Mark D., et al. “Early-Phase Muscular Adaptations in Response to Slow-Speed versus Traditional Resistance-Training Regimens.” European Journal of Applied Physiology, vol. 112, no. 10, 12 Feb. 2012, pp. 3585–3595, https://doi.org/10.1007/s00421-012-2339-3.
- Schoenfeld, Brad J., et al. “Effect of Repetition Duration during Resistance Training on Muscle Hypertrophy: A Systematic Review and Meta-Analysis.” Sports Medicine, vol. 45, no. 4, 20 Jan. 2015, pp. 577–585, https://doi.org/10.1007/s40279-015-0304-0.
- Nogueira, W., et al. “Effects of Power Training on Muscle Thickness of Older Men.” International Journal of Sports Medicine, vol. 30, no. 03, 6 Feb. 2009, pp. 200–204, https://doi.org/10.1055/s-0028-1104584.
- Wilk, Michal, et al. “The Influence of Movement Tempo during Resistance Training on Muscular Strength and Hypertrophy Responses: A Review.” Sports Medicine (Auckland, N.Z.), vol. 51, no. 8, 27 May 2021, pubmed.ncbi.nlm.nih.gov/34043184/, https://doi.org/10.1007/s40279-021-01465-2.
Garett Reid
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