Despite its key role in building muscle, time under tension and how it affects muscle growth rarely gets the recognition it deserves.
While high-intensity interval training (HIIT), lifting weights, and eating high-protein foods may get some attention, this ugly but effective training principle has been at the heart of strength training since the first free weights were invented. And it is still important in today’s home training, for example, when using the best adjustable dumbbells (opens in a new tab).
But what does time under stress mean? In short, it’s the total time your muscles work during an exercise, and it’s dictated by the number of repetitions you perform in each set, as well as the speed at which you perform them.
Varying the time under tension can change the stimulus of your workout, helping you target different aspects of fitness, such as muscular endurance, hypertrophy (opens in a new tab) or muscle power, says Jinger Gotshall, director of applied research at Wahoo Sports Science (opens in a new tab).
We spoke with Gottschal at length and examined the relevant research to find out how you can manipulate time under stress to get the most out of your workouts.
Jinger C. Gottschal received her PhD 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 assistant professor at Penn State University and studied the effectiveness of various exercise regimens for 12 years. For the past 25 years, she has coached endurance runners and triathlon athletes from recreational to professional. Most importantly, Jinger loves being physically active and appreciates the paramount importance of promoting balanced, quality exercise programs.
What is time under stress
Time under tension is simply the amount of time a muscle is under tension during exercise.
This includes both the eccentric and concentric parts of the lift; lengthening and shortening of the working muscle. For example, while the bulk of your effort is pushing the bench press up and away from your chest (concentric phase), your pectoral muscles will still be under tension as they control the downward movement of the bar (eccentric phase).
Some time manipulations under tension (or tempo training) may also use isometric contraction. Here, the length of the muscle does not change during the contraction – for example, in a wall sit, you remain stationary, but the leg muscles are still under tension.
Does time under stress build muscle?
For those who want to open how to gain muscle (opens in a new tab)it’s no exaggeration to say that without any element of time under tension, muscle gains (or hypertrophy (opens in a new tab)) in adults would be almost impossible.
“Muscle hypertrophy occurs when muscle protein synthesis exceeds muscle protein breakdown and results in a positive net protein balance over cumulative periods,” summarizes a 2019 study published in International Journal of Environmental and Health Research (opens in a new tab). “This can be achieved through both strength training and protein intake, which stimulates muscle protein synthesis and results in reduced muscle protein breakdown.”
In other words, you need to do some form of resistance training (such as lifting weights or using some of the the best resistance groups (opens in a new tab)) and eating enough protein if you want to build muscle. And during this resistance training, your muscles will be under tension for a while.
How does time under stress affect performance?
In gyms around the world, people follow these tips:
- Do heavy sets of four to six reps to build strength.
- Do 8-12 reps with a moderate weight to build muscle.
- Perform 12 or more repetitions with a lighter weight to improve muscular endurance.
Time under stress is the principle behind this. Consider:
- If you perform four bicep curls with a two-second eccentric (down) phase and a one-second concentric (up) phase, your biceps will be under tension for a total of 12 seconds.
- If you perform 12 bicep curls at the same pace, this figure increases to 36 seconds.
Ignore this as “bro science” at your peril.
“It’s critical to overload your muscles in a way that challenges your goal,” says Gottschall.
But, she adds, the pace and rep pattern with which you lift (both important factors in determining your total time under tension) will determine what aspect of fitness your training targets.
“If you want to gain muscular endurance, use lighter weights for more repetitions at a slower rate until volitional fatigue – in this case, volitional fatigue is the inability to continue due to muscular endurance. If you want to gain muscle power, use heavier weights for fewer repetitions performed at a faster speed until volitional fatigue sets in.’
Therefore, lifting lighter weights for more repetitions to increase the time under tension can help increase muscular endurance, or the ability of a muscle to repeatedly apply force to a load over a long period.
Meanwhile, lifting heavier weights with fewer repetitions for less total time under tension can help increase an athlete’s muscular power—the ability to generate explosive force in a short amount of time.
How long under tension for hypertrophy?
The two examples above focus on lifting lighter weights at a slower pace to improve muscular endurance or lifting heavier weights at a faster pace to build muscle strength. To increase muscle mass, you need to find a happy medium between the two factors. Gotschall recommends adding either weight or reps to your regular exercises.
You can also introduce tempo training where you vary the timing of the eccentric, isometric and concentric phases of your lifts to challenge the muscles with new stimuli.
“Spending more time in the eccentric phase of the movement increases the time under tension,” Gottschall says. “And several studies have shown that low-intensity training produces just as much hypertrophy as moderate-to-high-intensity training when you’re training to volitional fatigue.”
Even so, Gottschall says it’s difficult to determine an exact figure for the optimal amount of time under tension for muscle growth from the existing literature.
A 2011 study published in the Journal of Physiology (opens in a new tab) found that leg extension exercises performed at a slow tempo (six-second eccentric and concentric phase) and performed to fatigue resulted in a greater increase in muscle protein synthesis than the same movement performed rapidly. However, a 2015 study published in Sports medicine (opens in a new tab) journal contradicted this, concluding that the observed muscle hypertrophy was similar in the study group when training with different repetitions lasting from 0.5 seconds to eight seconds.
So, what kind of workout should you aim for if your goal is hypertrophy? A 2019 systematic review published in International Journal of Environmental and Health Research (opens in a new tab) advises someone who wants to maximize muscle mass to do 3-6 sets of exercises, each of which consists of 6-12 repetitions. Sets should be broken up into 60-second rest intervals. And keep the weights light – you should aim for a moderate intensity of 60 to 80% of your 1RM.
Want to keep growing? Then each week increase the training volume by 12-28 sets for each muscle.