TRAIN SMART: What is “Time Under Tension”?

Try to think back to your very first Corefire class: it was likely a blur of sweat, shaking muscles, heavy breathing and having to concentrate very intensely on what was being asked of you. Certainly not your typical workout, Corefire challenges both your body AND your brain, every single session. By understanding how and why we train the way we do, we are better able to connect mindfully to the movements, which leads to better muscular activation and engagement, and over time, results. In this TRAIN SMART series post, we will be discussing the concept of “Time Under Tension.” Expect to learn what it means, why it’s a safe and effective exercise approach, and what kind of results it can produce.

In the fitness world, “time under tension” generally refers to the amount of time you are applying resistance to a muscle group or body part. If you think of bodyweight exercises like squats and lunges, there are certain moments during the movements when you feel significantly more challenge and less challenge. Taking it a step further, adding additional resistance – say, in the form of dumbbells – will certainly increase the challenge of that movement. However, there are still moments where there is more work being done, and moments where you are pretty much at rest.
One of the incredible benefits of the Corefire workout is that ideally, you are working under pretty much constant tension. Let’s use the example of a bodyweight reverse lunge; when you step one foot back and bend both knees deeply, you should feel like you are working to balance and control your body. Even when you push off to step forward, you feel your muscles working. When you get to the top of that lunge, however, you are simply resting. The resistance you experience throughout the movement depends on your initial set-up of an exercise, the range of motion of your movement, and whether or not you are maintaining tension throughout.

Now consider the example of a Corefire Elevator Lunge. If executed mindfully and with good form, you should feel tension (read: work) throughout the entire range of motion of that movement. There are moments where you may feel more tension (at the bottom of the lunge) and less tension (as you approach standing), but you are still working. This illustrates the concept of time under tension.

By moving slowly and without using momentum, your body is forced to recruit more muscle fiber activation and hence, more work output. In general, the body naturally wants to take the path of least resistance; but by moving slowly and with control, you challenge both your body and your brain throughout the full range of motion of an exercise. In that same Elevator Lunge, if you start to increase your pace or depend on momentum, you will notice the resistance – and therefore, the challenge of the exercise – diminish.

According to a 2012 study researching time under tension and published in The Journal of Physiology, “results suggest that the time the muscle is under tension during exercise may be important in optimizing muscle growth.” In other words, to get a muscle to grow, utilizing time under tension can be one of several factors; you don’t necessarily need more repetitions, but better executed repetitions.

Additionally, the researchers “speculate that maximal fibre activation, and not percentage of maximal strength, is fundamental to induce maximal rates of muscle protein synthesis.” To increase muscular growth, it’s not about how heavy of a load you lift, but how much you activate your muscle fibers. Increasing your muscle activation can not only lead to muscular growth and increases in strength, but improvements across many health markers:

  • increased metabolism
  • maintaining healthy body fat percentage
  • improved blood sugar control
  • managing and/or avoiding chronic illnesses, such as diabetes
  • enhancing cardiovascular health
  • reducing blood pressure
  • improving cholesterol ratios
  • improving bone density and health

Time under tension offers a good example of what movement expert Gray Cook has thoughtfully articulated: “More is not better; better is better.” Rather than having a goal of executing a large number of repetitions (while likely moving quickly and without control), focus on executing those repetitions with good form and consistent, slow pacing.


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