Unless you’re fairly new to working out with weights, chances are you’ve heard about the concept of Time Under Tension.
So what does it mean, exactly?
Well, Time Under Tension relates to training with weights, or any other form of resistance, for that matter. To most people, it basically refers to the total length of time over which the target muscle group is placed under load during an exercise repetition.
And there are those who believe that to get optimal results from a training session, you should maximize that length of time.
This is why it’s not uncommon to see people training in the gym using very slow movements, with total repetition times of up to 6 to 10 seconds, and sometimes more. A typical way they would do this is by performing say a 2 or 3 second concentric (the muscle-contracting, or working, phase of an exercise repetition) and a 4 to 8 second eccentric (the muscle-extending, or releasing, phase of an exercise repetition).
The rationale is that the longer you hold the target muscle groups under tension during an exercise repetition, the more muscle growth you’ll experience. There are even more extreme advocates of Time Under Tension training out there who endorse total repetition times of up to 45 seconds.
The eccentric myth
Before we look at the validity of maximizing Time Under Tension during training, let’s take a brief sidebar here to discuss why it is that there’s so much time emphasis on the eccentric phase of an exercise movement.
Well, there are two reasons for this.
Firstly, the eccentric phase of an exercise repetition is always easier than the concentric phase, so it makes sense to add to its difficulty (to roughly match that of the concentric) by making it slower.
Secondly, there appears to be a widespread belief that the eccentric phase of an exercise movement is responsible for creating muscle growth, whereas the concentric isn’t. This is why some people tend to power through the concentric quite quickly, and then inch through a long, slow, drawn-out eccentric.
The problem is, this belief is actually incorrect.
Studies show that muscle growth (hypertrophy) is attributed to both the eccentric and concentric phases of an exercise movement, with possibly a little more coming from the eccentric phase, but not much more.
So, while having the eccentric phase longer than the concentric phase makes sense considering the first reason I mentioned above, there’s no valid reason for focusing solely on the eccentric for muscle development. Both phases are important.
The pros and cons of more time under tension
So with the time apportionment between concentric and eccentric cleared up, the $64,000 question is, is there really any benefit to extending the time under tension by slowing down exercise repetitions in general?
Well, studies do indeed show that more time under tension equals more muscle growth. So in theory at least, the Time Under Tension advocates are on the right track.
It’s in practice that their methods fall over, though. There are two considerations to look at to understand why.
Firstly, while Time Under Tension is a factor contributing to muscle growth, it’s not the only one. So it can’t be considered in isolation. Other important factors to take into account include intensity, or load; volume; rest period duration; speed of movement; and range of movement, among others.
Studies show that the most important factor that determines muscle growth, however, is training volume. All the other factors matter, but volume has the biggest influence.
Training volume is defined as:
Weight x No. of Reps x No. of Sets
It’s basically a measure of the amount of work done in a workout session.
The second consideration, then, is the effect of maximizing Time Under Tension on the all-important training volume.
While slowing down exercise repetitions to maximize time under tension may sound like a good idea in theory, it isn’t necessarily so when you consider that it almost always comes at the expense of training volume.
If your training is only relatively light, and not near your failure limits, then you would most likely be able to increase your Time Under Tension by slowing down your exercise repetitions, without affecting your training volume. You could use the same load, with the same number of reps and sets.
In this case, absolutely you would expect a benefit.
If you’re training intensely, however – at or near your failure limits, then because slower repetitions mean greater difficulty, something else would necessarily need to be sacrificed. And that is that either the amount of weight or the number of repetitions would need to be reduced.
So training volume would take a hit.
Why is it so?
OK, so moment ago I mentioned that studies confirm that more time under tension equals more muscle growth. But how can that be if, when training intensely, it inherently reduces training volume?
The answer to this lies in the definition of “Time Under Tension”.
Most people focus on increasing time under tension for each rep, as that’s what they believe “Time Under Tension” refers to. But the “Time Under Tension” that really matters is for the entire training session. Not each rep.
So there’s a trade-off here.
Increasing the Time Under Tension per rep may increase the Time Under Tension for the entire workout session somewhat. But on the downside, it usually leads to a reduction in intensity at the same time, and almost always a reduction in training volume as well.
So in effect, you’re giving with one hand, while taking something more influential with the other.
What this DOES NOT mean for your workouts
Now, given what I’ve just explained, there will be those who may be tempted to conclude that the best way to train is therefore to aim for the greatest possible number of repetitions, by performing them as rapidly as possible.
After all, that’s how to maximize training volume. And volume is king, right?
Well, again, you can’t look at one variable in isolation. This is why extremist thinking never works out in practice.
Imagine that you regularly perform bicep curls with 25lb dumbbells, for say 12 repetitions per set. Now assume that you decide to double your bicep training volume by reducing the weight by a factor of ten, to 2.5lb, and increasing the number of repetitions by twenty, to 240.
Do you believe that this doubling of volume will result in more hypertrophy of the biceps?
Most likely not. In fact, it will almost certainly decrease.
Because you’ve slashed the intensity, which is also an important consideration. And you will have reached a point where it becomes the determining factor.
Everything has its sensible “sweet spot” where things work best.
If increasing something is good, it doesn’t necessarily follow that increasing it ad infinitum is best.
The take home lesson about training tempo
One study looking into the effects of Time Under Tension training compared two groups of women over a six-week period, one that trained at a normal tempo of about 3 seconds per repetition, and another that trained at a slow tempo of 14 seconds per repetition (10 second concentrics and 4 second eccentrics), with correspondingly reduced intensity.
The normal tempo group experienced a 39% increase in muscle area, whereas the slow tempo group experienced only an 11% increase, despite the time under tension being almost five times greater.
This isn’t surprising when you consider that it has been shown that muscle activation is reduced to about one-third when slowing down exercise repetitions to 5 second concentrics and 5 second eccentrics with a corresponding reduction in intensity. Optimal hypertrophy relies on the recruitment of all the muscle fiber types, not just some.
The consensus among studies, then, is that the optimal training tempo for muscle hypertrophy is in the middle-of-the-road range – somewhere around 1-2 second concentrics, and 2-3-second eccentrics.
That seems to be the sweet spot.
Not ultra-fast to maximize volume, and not ultra-slow to maximize the time under tension.
But there’s one final point to consider.
Don’t take this conclusion to mean that that’s the tempo you should always train at. It’s certainly the tempo you should focus on the most if muscle growth is your goal.
But adding some variety into your training is also very beneficial. And that means some faster days and some slower, “Time Under Tension” days added into the mix.
By always doing the same old thing, your body ceases to be challenged.
Different modalities each have their own unique benefits to offer, and variety keeps your body from adapting to any one specialization. It keeps it out of its comfort zone, so to speak, so that you get the most development, especially where muscle growth is concerned.