Q: Hey Tom, I understand that Time Under Tension (TUT) is supposed to be an important factor for muscle growth. I’ve always heard that if your TUT isn’t long enough, you won’t maximize your gains. Supposedly the ideal length of a set is 40 to 70 seconds. It sounds logical, but is it really true? Where did that number come from? What if my set lasts only 30 seconds? If the set is still high-intensity, wouldn’t I make gains regardless of the exact rep tempo or duration?”
A: Time under tension (TUT) has been one of the most debated concepts in hypertrophy training. Many lifters believe that it requires 40-70 seconds of constant tension per set for optimal muscle growth, but does the science support this?
Let’s take a closer look at whether time under tension really matters for building muscle, or if other hypertrophy training variables are more important.
The short answer is: No – there is no magic 40–70 seconds of time under tension hypertrophy window for set duration.
Time under tension (TUT) is one of those bodybuilding theories that’s been circulating for years, but the idea that TUT training by itself is a major key to muscle growth simply isn’t accurate.
Like a lot of gym lore, the 40–70 second time under tension training rule started with good intentions. Bodybuilders wanted a simple way to make sure their sets were hard enough and long enough to produce a training stimulus.
So for decades, coaches repeated: “If you want to grow, you need at least 40 seconds of time under tension per set.”
Where Did the Time Under Tension Training Idea Come From – And Why 40–70 Seconds Became “The Rule”
Where the 40 to 70 seconds under tension number came from, I’m not sure. The origin is a bit murky. But here’s my best guess:
It didn’t come from experimental research. It began as a coaching rule of thumb in bodybuilding circles in the 1990s and 2000s. It mostly came from tempo training systems (for example Charles Poliquin), and maybe from HIT-style slow-repetition methods.
And here’s a logical explanation why coaches latched on to it:
Time Under Tension Vs Reps
Do the math. Suppose the most common rep tempo is 1–2 seconds up and 2–3 seconds down. Let’s call that an average of 4 seconds per rep. If the average set is 8–12 reps, then that’s 32 to 48 seconds – pretty close to the 40 second minimum.
And since a lot of bodybuilders like to accentuate the negative and sometimes go up to 15 reps for hypertrophy, that would explain a 70 second upper end of the range.
Since this does in fact trigger good hypertrophy responses, athletes and coaches treated that set duration (time under tension) as causative, even though it was just coincidental – a correlation.
But the idea stuck anyway, despite no direct scientific evidence that muscle growth requires a specific TUT window.
What Current Studies Say About Time Under Tension Training
Modern research has come a long way since the 1990s. The studies now show that hypertrophy can occur across a wide range of set durations, as long as the set is sufficiently challenging. (Within 1 to 2 reps of failure, and occasionally all the way to failure).
A study from the scientific journal Sports Medicine (Schoenfeld et al 2015) found that when a rep lasts anywhere between .5 seconds and 8 seconds, the muscle gains are similar.
Surprisingly to many people, if you do a rep with 1 second up and 1 second down and a rep with 4 seconds up and 4 second down, they both produce similar results. Slowing down the reps 4X doesn’t produce better gains when all else is equal. (But it does make the workout less time efficient).
In other words, time under tension is not a primary driver of muscle growth, and there is no magic in the 40–70 second TUT for hypertrophy zone. Your set does not need to hit a specific duration to work.
It’s TOTAL tension that matters for muscle growth, which means it’s more productive to look at volume load than TIME under tension. Volume load is weight X reps X sets.
Assuming that volume load hits benchmarks for optimal muscle gain, the set duration really doesn’t matter. However, lifting too slowly can be detrimental as you’ll see in a moment.
Why the Old Time Under Tension (TUT) Model Doesn’t Predict Muscle Growth
Time under tension simply means how long a muscle spends under load during a set. It sounds logical that more time under tension equals more growth. The problem is that “time” doesn’t tell you anything about the quality or amount of tension.
You could lift a light weight with a slow tempo for 70 seconds and still get almost no muscle gains. That’s because the weight wasn’t heavy enough and the intensity wasn’t high enough to recruit and fatigue the largest motor units and stimulate them to grow.
Time Under Tension Vs Heavy Weight
If you believed in the more TUT the better theory, you could prolong your sets even more than 70 seconds by doing super slow reps. But by using an excessively slow tempo, you force yourself to use super light weights. That only decreases your strength and muscle gains!
Pullout: Research shows that when a repetition takes longer than 10 seconds, the reduced poundage necessary to go that slow compromises your muscle and strength gains.
What’s more, you could also put in a meager effort and stop far short of failure with those lighter weights, have a long TUT, and get absolutely zero muscle growth because the quality of that set was so poor. Weight too light, intensity too low.
On the other hand, you could lift a challenging weight, with a somewhat fast rep speed like 1 second up and 1 second down, and train to failure or close to it, with a TUT of only 20–30 seconds and stimulate major muscle growth.
The stopwatch is not the key variable. Mechanical tension is.
Mechanical Tension vs. Time Under Tension: What Really Drives Muscle Growth
Modern hypertrophy science defines mechanical tension as “force production in muscle fibers over time,” which depends more on muscle fiber recruitment and load than on set duration.
That means the amount of tension on the muscle tissue matters more than how long there is tension. A set that creates higher muscular force – even for a shorter time – can be far more effective than a long set with low force.
This explains why both of the following build muscle:
- Heavy sets of 5–8 reps (shorter TUT)
- Moderate/light sets of 10–20+ reps (longer TUT)
The key?
First, both are taken close enough to failure to fully recruit and challenge the high-threshold motor units. (High enough intensity of effort).
Second, the total volume load of the whole workout meets thresholds for optimal hypertrophy.
So if your set only took 30 seconds, it doesn’t suddenly become “non-hypertrophic” because it fell short of the arbitrary 40 second minimum. And if your set takes 60 seconds, it isn’t necessarily superior unless it meets the criteria I mentioned above. What matters is whether the set was hard enough.
Now, at this point, you might be wondering:
“But wait a minute Tom, if my intensity is high enough and the weight is heavy enough, then doesn’t a longer set duration mean more tension?”
Yes, this is true. Which is why I’m not saying time under tension is a completely useless concept. However, it makes more sense to quantify that tension as volume rather than set duration alone.
There is definitely a correlation between time under tension and muscle gains when the load and intensity are optimal.
Remember, many hypertrophy-style sets – say, 8 to 15 reps at a moderate tempo – often happen to fall in that time under tension range. But that’s a coincidence of training style – not the basis of a major training guideline.
A lot of your sets may fall between 40 and 70 seconds. But some won’t. If your set took 30 seconds or 80 seconds, it doesn’t matter. You don’t need to time your sets and aim for a specific number of seconds.
Why Volume Load Matters More Than Time Under Tension (TUT)
Let’s assume you’re doing all your working sets in close proximity to failure (1 to 2 reps in reserve). When that box is already checked, there’s one variable that correlates better with hypertrophy than TUT. That is volume.
Volume can be quantified a couple ways:
- Hard sets per muscle per week
- Total volume load (sets × reps × load)
Think of it this way: 30 seconds under tension with 50 pounds produces more total work than 60 seconds under tension with 15 pounds.
The shorter, heavier set creates far more meaningful mechanical tension, even though the time is half as long and out of the so-called optimal TUT range.
This is why the time-under-tension obsession has faded in recent years as the research has matured. But the idea that TUT training is most important is still circulating widely. That’s probably because it sounds plausible, and the idea was promoted for so many years, so it dies hard.
But the modern research supports what I’m saying. A 2015 meta-analysis on repetition tempo showed hypertrophy across a wide range of set durations, not just 40 – 70 seconds. Later science reviews in 2019 and 2022 confirmed that as long as sets are challenging and total volume is sufficient, muscles grow with both short and long time-under-tension ranges.
Also, the newest systematic review and meta-analysis of rep speed and hypertrophy (Schoenfeld et al 2025) confirmed that there’s not much difference in muscle gains between slower and faster repetition tempos. This suggests that how slowly you lift is far less important than overall load, intensity of effort and volume
Is Time Under Tension A Myth? Is It Useless?
The TUT concept is not useless, it’s just not a top-priority variable and not the number to focus on the most.
However, when you think about tension on the muscle, there is one key point to remember: Stay in control of the weights.
On the way up, don’t use momentum. Don’t swing the weights up. On the way down, don’t drop the weights. Think “fight gravity.” Lift with good form and a steady cadence. Remember, if you heave the weight up with body English, or just drop the weight on the eccentric, you’re reducing the tension.
This is part of proper form and it’s important for maximizing tension. A controlled rep also helps improve your mind to muscle connection and reduces the risk of injury.
There’s also something to be said for continuous tension. If you were to pause between every rep, you could still achieve a high total volume load, which most directly is responsible for your muscle gains.
But if you do at least some of your training with continuous tension, where you not only avoid using momentum, but also avoid pauses between reps, you increase metabolic stress. You get a great pump as well.
This is a secondary factor that may stimulate muscle gains. In addition, continuous tension training allows you to stimulate hypertrophy with lighter weights. That’s valuable for people who struggle with joint pain – which especially includes older trainees.
You can make a light weight feel heavier with techniques like continuous tension and make gains without joint pain.
But you don’t need to count how many seconds your set takes. You don’t need to follow a tempo prescription like “3-1-1” or 3-0-3-1. You don’t need a time under tension workout that you track with a stopwatch.
Just train hard, stay within your target rep range, take the set near failure, and hit optimal volume benchmarks.
What to Focus on Instead of Time Under Tension for Maximum Muscle Growth
If your goal is building muscle (hypertrophy training), prioritize these hypertrophy training variables – in this order:
- Train close to failure (1–2 reps shy for most sets). That’s a “hard effort.”
- Use a load that’s challenging in your target rep range. The last couple reps should feel hard.
- Use good form and control the reps so tension stays on the target muscle the whole set.
- Hit enough weekly volume (for most people, 10–20 sets per muscle per week for major muscle groups. A little less for small muscles or when using ultra-high intensity).
- Increase the load or reps over time. (Use progressive overload).
If you do these 5 things, you’re going to gain muscle regardless of what the time under tension is.
Final Verdict: Does Time Under Tension Really Matter?
Bottom line: The 40–70 second “optimal time under tension” rule is not supported by current research.
Muscle growth does not depend on hitting a specific time under tension duration. Shorter sets can build muscle. Longer sets can build muscle. The key is forcing your muscle fibers to produce high levels of mechanical tension, and taking your sets close to failure.
If someone tells you your set “didn’t count” because it was 28 seconds, you can politely ignore that. You don’t have to obsess over time under tension if you train enough and train hard. Don’t overcomplicate the basics.
-Tom Venuto
Summary / FAQ: Time Under Tension (TUT)
Q: Do I need 40–70 seconds of time under tension to maximize muscle growth?
A: No. There’s no research showing a magic 40–70 second hypertrophy window. Sets of many different durations can build muscle as long as they’re challenging.
Q: What matters more than TUT for stimulating hypertrophy?
A: Mechanical tension and effort. Use a load heavy enough to recruit the largest motor units, and take the set close to failure. That drives growth – not the stopwatch.
Q: Is time under tension completely irrelevant?
A: Not at all. TUT is helpful indirectly because controlled reps keep the tension on the muscle and prevent momentum. But duration itself is not a priority training variable.
Q: Why can short sets and long sets both work?
A: Because muscle responds to force + effort, not minutes and seconds. Heavy sets of 5–8 reps (short TUT) and moderate/light sets of 10–20+ reps (long TUT) both work if the set is taken close to failure.
Q: What is the simplest way to train for maximum muscle growth?
A: Work hard, use good form, train to near failure, hit enough weekly sets (10–20 per muscle group for most people), and progressively add weight or reps over time.
Do this consistently and your muscles will grow, regardless of whether a set lasts 20 seconds or 80 seconds.
About Tom Venuto
Tom Venuto is a natural bodybuilding and fat loss coach with 35 years of experience. He holds a degree in exercise science and has trained hundreds of clients in person. He is also a recipe creator specializing in fat-burning, muscle-building cooking.
A former competitive bodybuilder, Tom is now a full-time evidence-based fitness writer, blogger, and author. His classic book Burn the Fat, Feed the Muscle is an international bestseller, first as an ebook and later as a hardcover and audiobook. His newest book. Extreme Fat Loss, which analyzes controversial diet and training programs, became an instant bestseller in 2025.
Tom’s work has been featured in Men’s Fitness, Oprah Magazine and dozens of other major publications. He is best known for his no-BS, evidence based approach to natural fat loss and muscle-building.
Tom is also the founder of Burn the Fat Inner Circle, a fitness support community with more than 53,000 members worldwide since 2006.
Scientific references
Bernárdez-Vázquez, R et al, Resistance training variables for optimization of muscle hypertrophy: An umbrella review. Frontiers in Sports and Active Living, 4, 949021, 2022.
Burd, N, et al, Muscle time under tension during resistance exercise stimulates differential muscle protein sub-fractional synthetic responses in men. Journal of Physiology, 590(2), 351–362, 2012.
Morton, R, et al, Training for strength and hypertrophy: An evidence-based approach. Current Opinion in Physiology, 10, 90–95, 2019.
Morton et al, Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men, Journal of Applied Physiology, 121:1, 129-138, 2016
Schoenfeld B et al, how slow should you go? A systematic review and meta-analysis of the effect of resistance training repetition tempo on muscle hypertrophy, Journal of Strength and Conditioning Research, 39:12, 1331–1339, 2025
Schoenfeld, B et al, The mechanisms of muscle hypertrophy and their application to resistance training. Journal of Strength and Conditioning Research, 24(10), 2857–2872, 2010.
Schoenfeld, B et al, Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. Journal of Strength and Conditioning Research, 29(10), 2909–2918, 2015.
Schoenfeld, B, Ogborn, D, Krieger, J, Effect of repetition duration during resistance training on muscle hypertrophy: A systematic review and meta-analysis. Sports Medicine, 45(4), 577–585, 2015.
Related Articles:
Leave A Comment