Time under tension: Here's how it actually affects muscle growth

Despite playing a pivotal role in building muscle, time under tension and how it affects muscle growth rarely gets the recognition it deserves.

While the likes of high intensity interval training (HIIT), heavy lifting and high protein foods may steal the limelight, this unglamorous yet effective training principle has underpinned strength training from the day the first free weight was made. And it continues to be important in modern home workouts such as when using the best adjustable dumbbells. 

But what does time under tension mean? In short, it’s the total time your muscles are working during exercise and this is dictated by the number of repetitions you complete in each set as well as the speed at which you complete them. 

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Varying time under tension can alter the stimulus of a workout, helping you to target different facets of fitness such as muscular endurance, hypertrophy or muscular power, says Jinger Gottschall, director of applied research at Wahoo Sports Science. 

We’ve spoken to Gottschall at length and examined relevant studies to explore how you can manipulate time under tension to get the most out of your workouts.

Jinger Gottschall

 Jinger S. Gottschall earned her doctoral degree in integrative physiology from the University of Colorado at Boulder and continued her academic career as a postdoctoral fellow in neurophysiology at the Emory School of Medicine. She was an associate professor at The Pennsylvania State University studying the effectiveness of various exercise regimens for 12 years. For the last 25 years she has coached running and triathlon endurance athletes from the recreational level to the professional.  Most importantly, Jinger has a passion for physical activity and appreciates the paramount importance of promoting balanced, quality training programs. 

What is time under tension

Time under tension is simply the amount of time a muscle is under tension during a workout. 

This includes both the eccentric and concentric portions of a lift; the lengthening and shortening of the working muscle. For example, while the bulk of your effort is used in pushing a barbell bench press up and away from your chest (the concentric phase) your pectoral muscles will still be under tension as they control the descent of the bar (the eccentric phase). 

Some manipulations of time under tension (or tempo training) may also utlilize an isometric contraction. This is where the muscle length does not change during contraction – for example, a wall sit, where you remain stationary but your leg muscles are still under tension. 

Does time under tension build muscle?

For anyone wanting to discover how to gain muscle, it’s no exaggeration to say that, without some element of time under tension, muscle gain (or hypertrophy) in adults would be nigh on impossible. 

“Muscle hypertrophy occurs when muscle protein synthesis exceeds muscle protein breakdown and results in positive net protein balance in cumulative periods,” summarized a 2019 study published in the International Journal of Environmental Research and Public Health. “This could be achieved with both resistance training and protein ingestion, which stimulates muscle protein synthesis and leads to decreases in muscle protein breakdown.”

In other words, you need to be doing resistance training in some form (such as by lifting weights or using some of the best resistance bands) and eating enough protein if you want to grow your muscles. And during that resistance training, your muscles will need to be under tension for a portion of time.

How does time under tension affect performance?

In gyms across the world, people follow the approximate advice of:  

• Doing heavy sets of four to six reps for strength gains. 
• Completing eight to 12 reps at a moderate weight to build muscle.
• Doing 12 or more reps at a lighter weight for improvements in muscular endurance. 

Time under tension is the principle behind this. Think: 

• If you perform four bicep curls with a two second eccentric (downward) phase and a one second concentric (upward) phase then your biceps will have been under tension for a total of 12 seconds.  
• If you perform 12 bicep curls at the same tempo, this figure is bumped up to 36 seconds.  

Disregard this as “bro science” at your peril though.

“It is critical to overload the muscle in a manner that will challenge it toward your goal,” Gottschall says.

But, she adds, the tempo and rep scheme with which you lift (both critical factors in deciding your overall time under tension) will determine which facet of fitness is targeted by your training.

“If you want to gain muscular endurance then use lighter weights for a higher number of reps with a slower speed until volitional fatigue – in this instance, volitional fatigue is the inability to continue due to muscular endurance. If you want to gain muscular power then use heavier weights for a lower number of reps completed with a faster speed until volitional fatigue.”

So lifting lighter weights for more reps to create greater time under tension can help build muscular endurance, or the ability of a muscle to repeatedly exert force against a load for a prolonged period. 

Meanwhile, lifting heavier weights for fewer reps to create lower time under tension overall can help increase an athlete’s muscular power – the ability to produce explosive force for a short amount of time.

How much time under tension for hypertrophy?

The two examples listed above focus on lifting light weights at a slower tempo to improve muscular endurance or lifting heavier weights at a faster pace to build muscular power. For muscle gain, a happy medium between the two factors must be found. Gotschall recommends adding either weight or repetitions to your usual exercises.

You can also introduce tempo training, where you vary the time of the eccentric, isometric and concentric phases of your lifts, to challenge your muscles with new stimuli.

“Spending more time in the eccentric phase of the motion increases time under tension,” Gottschall says. “And several studies reported that training with low-loads results in similar hypertrophy to training with moderate and high-loads when you train to reach volitional fatigue.”

Even so, Gottschall says it's hard to draw an exact figure of the optimal amount of time under tension for muscle growth from the existing literature. 

A 2011 study published in The Journal of Physiology found that leg extension exercises completed at a slow tempo  (a six second eccentric and concentric phase)  and done until fatigue produced a greater increase in muscle protein synthesis than the same movement performed rapidly. Yet a 2015 study published in the Sports Medicine journal contradicts this, concluding that observed muscle hypertrophy was similar in a study group when training with various reps that lasted anywhere from 0.5 seconds to eight seconds. 

So, what sort of workout should you be aiming for if hypertrophy is your goal? A 2019 systematic review published in the International Journal of Environmental Research and Public Health advises that anyone who wants to maximize muscle growth should do 3-6 sets of an exercise, with each set consisting of 6-12 repetitions. The sets should be broken up by 60 second rest intervals. And put down the light weights – you should be aiming for a moderate intensity of 60 to 80% of your 1RM. 

Want to keep growing? Then increase the training volume by 12-28 sets for each muscle, each week.