Time Under Tension and Building Muscle—Does It Matter?

Clap your hands if you’ve heard this one before:

“Muscles don’t know weight, only tension.”

It’s an old bodybuilding saw that’s been around for decades, and it’s shorthand for the theory that the key driver of muscle growth is how long your muscles are working (contracting) during your workouts. 

For example, if you do one set of 8 reps and each rep takes about 5 seconds, your time under tension for that set is 40 seconds (8 x 5). If you do three sets of the exercise, your total time under tension is 120 seconds (40 x 3).

According to proponents of this idea, the more time under tension you rack up over days, weeks, months, and years of training, the more muscle you’ll gain more or less regardless of any other training variable (intensity, frequency, volume, etc.).

Is this true, though? Is time under tension really the biggest lever you can pull to build muscle? 

Not really.

You see, time under tension is an important element of the training stimulus that produces muscle growth, but it’s best to think of it as a byproduct of proper training rather than a target in its own right.

Let’s find out why.

Table of Contents

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• What Is Time Under Tension? 
• Is Time Under Tension Important for Building Muscle?
• What You Should Focus on Instead of Time Under Tension
• The Bottom Line on Time Under Tension

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What Is Time Under Tension? 

Time under tension refers to the total amount of time a muscle remains contracted. 

If you do 3 sets of 8 reps of biceps curls, and each rep takes 3 seconds, for instance, your time under tension would be 72 seconds. And if you do that twice per week, your weekly time under tension for your biceps would be 144 seconds (assuming you didn’t do any other biceps exercises during the week).

Simple enough. 

When talking about muscle hypertrophy, it’s just as important to understand what time under tension isn’t, too. It’s not the same as tension, or mechanical tension, which refers to how hard you’re contracting a muscle during an exercise (how much force it produces when it contracts). To ensure we don’t get these terms mixed up, I’ll refer to this as absolute tension.

Nearly every credible fitness researcher, coach, and expert acknowledges that making your muscles contract forcefully (absolute tension) is vital for gaining muscle, but some people claim that maximizing contraction time is even more so.

For instance, a proponent of the primacy of time under tension would argue that 3 sets of 8 slow (5-second, let’s say) reps of barbell curls with just 40 pounds (120 seconds of time under tension) is superior to 3 sets of 6 normal (2-second) reps with 60 pounds (36 seconds of time under tension). 

Summary: Time under tension refers to the total amount of time a muscle remains contracted. Some people claim this is the primary mechanism that drives muscle growth because “muscles only know tension, not weight.”

Is Time Under Tension Important for Building Muscle?

Yes, time under tension is important for building muscle, but research shows that in order for it to contribute to meaningful muscle growth, you also need to be using sufficiently heavy weights (~60% of one-rep max or higher). 

That is, if a weight isn’t heavy enough, it isn’t likely to stimulate much growth no matter how much time under tension you produce with it.

What’s more, as your muscles get stronger, they can produce more absolute tension, so a weight that’s difficult (and effective) today will be less so several months from now. Thus, to keep gaining muscle, logic would dictate that you’d need to keep adding weight to the bar and dumbbells. And that’s mostly correct.

This process is known as progressive tension overload, and studies show that it’s the foremost mechanical factor involved in muscle growth. It’s the primary determinant of how big and strong you get from your training.

Read: Is Getting Stronger Really the Best Way to Gain Muscle?

And that brings us to the biggest problem with focusing exclusively on time under tension: it can hamper your ability to achieve progressive overload. 

For example, the most common method of increasing time under tension in a workout is slowing down reps.

This technique is popular because it certainly feels like your muscles are working overtime, but it’s actually a classic example of stepping over dollars to pick up dimes because it requires you to use much lighter weights.

For example, if you can bench press 225 pounds for 5 normal (relatively fast) reps, if you want to slow down to 5 to 6 seconds per rep, you’ll likely have to reduce the weight to around 185  pounds or less.

And that dramatic drop in load is enough to hobble your gains.

A good example of this effect comes from a study conducted by scientists at the Federal University of São Carlos. The researchers had 12 trained men aged 18 to 30 do two workouts of three sets of leg press to failure using 80% of their one-rep max.

Half of the subjects were allowed to raise and lower the weight using whatever weightlifting tempo (speed) they wanted, which worked out to around 2.6 seconds per rep on average. The other half were forced to lower the weight in 2 seconds and raise the weight in 2 seconds, so that each rep took a total of 4 seconds. 

Then, both groups switched, and the weightlifters who were allowed to self-select their weightlifting tempo were forced to take 4 seconds to finish each rep, and vice versa. 

Despite racking up almost 40% more time under tension when using the slower weightlifting tempo, the subjects in this study were able to do about 60% more total reps when they used a faster weightlifting tempo. On the whole, this translated into much more total “work” (weight x reps) being done, producing more powerful muscle-building stimulus. 

An earlier study conducted by scientists at Springfield College found almost the same results using the bench press, and many other studies have reached a similar conclusion: 

Reducing load to increase time under tension only decreases the effectiveness of your training.

There are other ways to increase time under tension, too, but none are worthwhile. For example . . .

• Very high-rep, low weight sets produce a lot of time under tension, but most research shows they’re no more effective (and in some cases, less so) than lower-rep, higher-weight training.
• Many bodybuilders use short rest periods (90 seconds or less) between sets to do more reps per workout, but studies show this almost always results in worse muscle and strength gains.  
• Taking every set to absolute muscular failure can inject a little more time under tension into your training, but once again, research shows this is no better than and often inferior to ending sets a couple of reps shy of failure.
• Extremely high-volume training plans such as German Volume Training produce a ton of time under tension, but also appear to be less effective than moderate-volume plans.

Needless to say, you don’t want to make the mistake of completely neglecting time under tension, either.

There’s a school of bodybuilding that states that absolute tension is all that matters for muscle growth, and so if you’re willing to train with heavy enough weights, you can optimize your results with just a couple of intense lifting sessions per week.

For example, instead of doing 10 sets of bench press per week with, let’s say, 75 to 80% of your one-rep max, you could do just 2 or 3 sets with 95% and gain more muscle and strength.

Research shows that this is false, too. 

Yes, you need to lift heavy weights (generate large amounts of absolute tension) to get bigger and stronger, but you also need to do enough volume (produce enough time under tension) as well.

What is the most effective method of effectively increasing time under tension, then? Keep reading to find out. 

Summary: Time under tension is important for building muscle, but it shouldn’t be the primary focus of your training.

What You Should Focus on Instead of Time Under Tension

At bottom, the recipe for muscle growth is simple: 

Contracting your muscles with a sufficient amount of force (absolute tension) for a sufficient amount of time (time under tension) each week. Or put differently, doing enough heavy resistance training. 

We’ve already discussed what “heavy” means and how to use progressive overload to continue generating large amounts of absolute tension in our muscles, but what about time under tension? What’s “enough”?

Fortunately, you don’t have to attempt to directly record and manipulate time under tension itself (“Yes! 772 seconds of time under tension for my quads this week!”). 

Instead, you can focus on training volume, which can be measured in many ways, but research shows that “sets taken close to the point of muscular failure” (known as hard sets) is one of the most useful methods.

The prescription is equally simple, too:

The sweet spot for training volume is 10 to 20 hard sets per muscle group per week, with the smaller number more suitable to novices and the larger number to advanced trainees. If you do that, you’ll produce enough time under tension to optimize muscle and strength gain.

(And if you’d like even more specific advice about how many sets you should do each week, how often you should train, and what exercises you should do to reach your health and fitness goals, take the Legion Strength Training Quiz, and in less than a minute, you’ll know the perfect strength training program for you. Click here to check it out.)

So, to summarize, the best way to balance our muscles’ need for absolute tension and time under tension is . . .

• Train with 60 to 90% of one-rep max
• Do between 2 and 15 reps per set (a mix of different rep ranges is ideal for experienced weightlifters in particular)
• Do 10 to 20 hard sets per muscle group per week
• Use a normal (faster) rep tempo
• Rest 2 to 3 minutes between sets

If you follow that blueprint, you’ll avoid many of the pitfalls that prevent progress.

Summary: The best way to ensure you give your muscles the right mix of absolute tension and time under tension for building muscle is to add weight or reps to all of your exercises over time, do anywhere from 2 to 15 reps per set, and do 10 to 20 sets per muscle group per week.

The Bottom Line on Time Under Tension

Beware people who claim that any single method is the ONE TRUE WAY™ to get bigger, leaner, or stronger.

While building a body you can be proud of is fairly straightforward, it’s also multifaceted. Losing fat and building muscle don’t pivot on any single habits, behaviors, or hacks. 

Time under tension is a good example of this fact. While it’s an important aspect of muscle building, it’s not an end in itself that you can profitably pursue in many ways like very high-rep, very high-volume, or very slow training.

Instead, you must achieve adequate time under tension and absolute tension in your training, and that requires high amounts of resistance (heavy weights) and sufficient training volume (enough hard sets per week).

What’s your take on time under tension? Have anything else to share? Let me know in the comments below!