It's Time to Forget about Time Under Tension (TUT)
One of the first strength coaches I read extensively was the late Charles Poliquin – before he went off the rails and was kicked out of the company bearing his name.
- The Poliquin Principles
- Modern Trends in Strength Training - Volume 1 – To my knowledge there was never a volume 2, so I'm still not sure why it's Volume 1, maybe he never got around to finishing volume 2?
The latter is nearly impossible to find these days for a reasonable price. I just looked it up and paperbacks are anywhere from USD$150-900. It's a good book, but not THAT good. It's very short too.
Trust me, you don't need to invest that much in it, unless you're a meathead, a training historian or a strength and conditioning coach. Although $8 for a kindle version of the Poliquin Principles? Not bad...
Poliquin had a lot of great ideas back in the day – and some bad ones too as we all do.
Many ideas I later learned he had taken from other prominent strength coaches before him, sometimes with credit, sometimes without. A lot of them came from Australian S&C coach Ian King, whose equally good book "Get Buffed" is also hard to find but can be obtained for a mere USD$70 or so.
Yes, I have all of these books, and no I did not pay anything close to this much money for them because back in the early 2000's they were relatively inexpensive and easy to acquire. Yeah, that's how long I've been a personal training and S&C coach. 😳
While I don't view myself as training historian or anything I have a lot of old training and physical therapy books. I think it's good for your future reasoning skills to go back and determine where ideas came from.
Time Under Tension is one of those ideas.
And it's time this idea died.
What Is Time Under Tension?
TUT for short, is an idea that King and Poliquin probably popularized. In a perfect world you'd use a metronome to determine how long each part of a repetition lasted and this would tell you how long a muscle was "under tension" in relation to the desired outcome.
It is based on tempo or cadence prescriptions. For those that don't know, I wrote an article on tempo training notation eons ago.
Tempo is a 3 or 4 digit notation system used to prescribe lifting speeds. You'll find it in many training programs along with sets, reps and rest prescriptions.
For example, if I prescribe a 4010 tempo (4 seconds down, no pause, 1 second up, no pause) for 8 reps, then the TUT is 5 seconds x 8 = 40 seconds. If I prescribe a 201 (3 digit notation, 2 seconds down, no pause, 1 second up) tempo for 8 reps, then the TUT is 3 seconds x 8 = 18 seconds. I'd never do this, but if I prescribed 4444, then the per repetition TUT is 16, if I did that for 5 reps, then I'd have a TUT of 80 seconds.
It's the total time each set takes and 'theoretically' is a way to track a tension stressor but in practice ends up as nothing useful.
It doesn't matter if the concentric is 9 seconds long (1090) or the eccentric is 9 seconds long (9010) or there is a pause at the bottom (1810) or this is distributed more evenly (4242). All of those tempos have a TUT of 10 seconds per rep.
And very quickly I think you should be able to see what's wrong with this notion ...
Not all of those tempos can possibly be putting the same amount of true mechanical tension on the muscle itself, despite the same duration each set lasts.
Why People Thought This Mattered
At the time, there was (and still is) some research showing that longer eccentric (lowering phase) movements lead to more (or better) muscle growth.
Longer slower eccentrics in the 3-5 second range in particular – Note: This is likely the only variation that matters for growth in the grand scheme of things.
Unfortunately the majority of that research looked something that at the time was thought to be a proxy for growth → Androgen Hormone Response.
In those days, the thinking was androgens (like testosterone) cause growth, so spiking them higher naturally must yield more growth too! And these compounds do when they are added to the system ala anabolic steroids.
Unfortunately, natural spikes of these hormones don't mean a lot as a proxy for growth we later learned. In fact, the opposite appears to be true, as cortisol – a catabolic hormone; the antithesis of anabolic hormones – has the strongest correlation with ACTUAL growth.
Go figure. So spike your hormones as high as you want for all the difference it'll make. It's simply not the proxy we thought it was.
If some is good, more must be better. Right?
If a slow eccentric lasting 3-5 seconds shows improved muscle growth outcomes? Then slowing it down even further, or slowing down other parts of the lift down even more must yield even better hypertrophy. Right?
This is a common logical fallacy trap that an endless number of people fall victim to. Ultimately people run away with an idea and you end up with a lot of stupid long tempo recommendations all in the name of yielding more TUT.
That 4444 I wrote above is kind of a dumb tempo to use on so many levels, but it's not even the dumbest tempo I've seen on the internet. I've seen 10 second concentrics recommended! Which is just silly, and I'll explain why in a minute.
Let me be clear:
A meta-analysis of tempo speeds from 2015 found that any tempos yielding a TUT of 0.8 - 8 seconds in length yielded essentially the exact same amount of growth. And anything longer than that, yielded WORSE hypertrophy outcomes.
Which basically means any reasonable tempo works, long or short, but there is an upper limit.
The Stretch Shortening Cycle
The second reason people thought TUT matters is mentioned quite a bit by King. There is research showing that a slow eccentric action and a pause at the bottom of a lift eliminates (or greatly reduces) the stretch shortening cycle.
AKA The Stretch Reflex.
The thinking here is that if you eliminate the stretch reflex as much as possible, you reduce elastic energy storage and usage. Tendons store elastic energy during the eccentric part of the lift. The faster the eccentric, theoretically the more elastic energy you can store, and the more weight* you can lift.
*Note: The more weight you can lift might have additional benefits for growth on its own.
And you can see this in action at every gym across the world. People with faster lifting tempos can generally lift more weight because more elastic energy is contributing. Meaning (in theory) less direct stress is being applied to the muscle.
This is also the basis of plyometric (AKA shock) training. Given that we also know plyometrics are generally poor at building muscle when compared to dynamic resistance training. Then the easy assumption to make is elastic energy doesn't stress the muscle directly or well enough because of the elastic energy that contributes to the lift, reduces the direct muscle fibre stress.
Great in theory, except people forget that plyometrics are typically done for velocity and with significantly less loading that lifting is. Of course they aren't going to build much muscle.
In any case, this theory of pausing at the bottom to try and get more direct stress on the muscle and less stress on the tendons (via elastic energy storage) might not hold up.
We'd probably have seen some research by now suggesting that a pause at the bottom yielded better hypertrophy than no pause and an equivalent amount of eccentric lowering duration. But that doesn't seem to be the case. i.e. a 3-5 second pause should (again "in theory") yield the same or similar amount of hypertrophy as a 3-5 second eccentric.
Admittedly there isn't much hard data on this yet, but anecdotally, I can't say I've observed much of an beneficial effect of a long pause at the bottom of most lifts. At least not a better growth response over a slow controlled eccentric.
With the notable exception of the the calves. Adding a slight pause at the bottom of calf raises so people don't bounce out of the bottom seems to help with growth. Probably has more to do with the fact that people rush calf work really. Keeping in mind that the achilles tendon is particularly thick and elastic.
I've noticed less impact on the relatively large patellar tendon (the front of the knee). Possibly because of the way quad work is typically done (slow and controlled). Other than the calves, adding a pause doesn't really seem to matter that much in practice for any other muscle groups I can think of.
A really slow eccentric (3-5 seconds) probably reduces the stretch reflex enough as it is. Add a slight pause at the bottom and it probably amounts to a similar 3-4 second bottom pause equivalent anyway. A 3210 or 4110 tempo are two particular favourite tempos for calf work.
If the theory of stimulating repetitions turns out to be correct, then the type of mechanical stress you're looking for is really during the dynamic part of the lift near the end of each set anyway; After a certain amount of fatigue has been generated. And that mechanical stress will occur regardless of the intended lifting speed. You see the concentric muscle action slow down dramatically and universally at a certain point in any given set – usually the last 3-4 reps before hitting absolute failure.
On the surface, this appears to be the thing that matters most.
And that might explain why TUTs of 8 seconds or less all generate roughly the same hypertrophy. The research didn't break it down enough but I bet it mostly featured the same controlled eccentric (2-5 seconds) and the concentric was what was likely modified the most for manipulating TUT beyond that.
Long concentrics influence the amount of weight you can handle, substantially more than longer eccentrics. You're considerably stronger during the eccentric part of the lift. Slowing down the eccentric just doesn't have as large an impact on the weight you can move.
Ultimately the weight on the bar, stack, machine, bell, what have you; Is still the best thing to consider for growth in a moderate rep range. More weight on the bar = more of a stimulus for growth. Less total weight for the sake of slower lifting speeds = less of a stimulus for growth. There simply isn't enough weight to generate the true mechanical tension needed.
The Problems With Time Under Tension
The main problem with tracking and considering TUT as a training variable is that clearly not all Time Under Tension is created equal.
That meta-analysis above looked at a variety of tempos but mostly just calculated total TUT for the analysis. Falling victim to the initial problem with TUT; That not all parts of the lift create the right kind of tension for growth.
Other papers have looked more directly at this, and it appears that slower controlled eccentrics (within reason) appear to work a little bit better for growth than faster eccentrics.
However, the concentric part of the TUT equation appears to matter very little*. You can try this at home or in the gym with nearly any kind of lift to see what I mean.
*Which isn't to say that the tempo of the concentric doesn't matter at all. It does. But it only matters if you're working with intensities or rep ranges >8 reps and towards the end of the set.
You should see the rep speed slow involuntarily on the concentric part of the lift towards the end of the set if hypertrophy is the goal. This indicates you are getting close to failure and training close to failure is more important the further your sets move away from about 8 reps.
Grab any weight you'd normally do for say 8 reps in a given exercise (i.e. a weight that you can only lift 8 times). Do it with your normal lifting speed. Wait 2 days (so recovery isn't impacting this result) and try to do that same weight for 8 reps with a 9 second concentric. I'd be comfortable making a bet you stop after 5-6 reps. It's hard to lift things concentrically slow.
Voluntarily slow concentrics in practice limit the weight you can use, which again, impacts growth. Pauses after a concentric once you're done the rep? We know that isometric training isn't that great a hypertrophy stressor either; Despite there being static 'tension' on the muscle. Simply holding a weight at the top of a lift, doesn't generate much hypertrophy at all.
Okay so what about pauses after the eccentric? This is debatable.
There is no good research I'm aware of showing that a pause after the eccentric is of any benefit for hypertrophy. However, since there is no research, there is at least some reason to believe this might be true. Although I sincerely doubt it's a real difference maker on anything other than improving technique and reducing bounce.
If you're already doing a slower eccentric (3-5 seconds) then you've eliminated quite a bit of the stretch reflex anyway. This might make a pause redundant, provided there is no bouncing at the bottom of the slow eccentric on the transition back to the concentric.
I know it's hard to keep those two words separate in your mind!
Note: Pausing at the bottom of a lift is great for motor learning and developing starting strength at that joint angle. There are other reasons to do it, just not necessarily growth.
I might recommend a pause of 1-2 seconds if people are bouncing too much out of the bottom of a lift. Again, this is probably more of a technique improvement, taking stress of the tendon and putting it onto the muscle.
Fast eccentrics are good for tendons and tendons do influence muscle capacity to some degree, but that's a separate concern from TUT and growth.
More TUT ≠ Better Mechanical Tension
I say this a lot, but you cannot simply do more of something and expect it to universally be better, there is almost always a limit.
Even Poliquin knew this back in the day to some degree when he capped his recommended TUT for growth to sets not exceeding 70 seconds in length (20-70 seconds was his recommended set duration for growth).
Assuming his recommendation of 6-20 reps being 'optimal for growth' – and I actually disagree with this but that's a topic for another article – you end up with a wide variety of tempos:
- 20 reps x 1 total second = 20 seconds (e.g. 10x0 → "x" is notation for explosive)
- 6 reps x 4 total seconds = 24 seconds (e.g. 3010 or 2110)
- 20 reps x 3 total seconds = 60 seconds (e.g. 2010 or 1110)
- 6 reps x 11 seconds = 66 seconds (e.g. 8030 or 7210 → this one will be way above the threshold I mentioned earlier)
They can't all be right. Especially that last one.
While the intent was good; Give people a decent ballpark figure to shoot for. The execution isn't quite there and you can end up with a variety of useless tempos that people can and will try needlessly. Simply because they fit within the timeframe a prominent strength coach gave once upon a time.
And this happens often in the fitness community. Some coaches or salespeople online just run away with an idea and apply that 'more-is-better' ethos because they know people will buy into the concept. It makes sense to our surface level psychology.
The same way someone will market 6-minute abs to people who bought 7-minute abs because 6 is faster than 7. It's a race to the bottom and the people who lose out are the client/consumer, while skeezy people make mad bank manipulating your lizard brain.
King's recommendations were a little more specific:
- 20-40 seconds TUT for a good mix of strength and hypertrophy
- 40-70 seconds TUT for a good mix of hypertrophy and endurance
Can you see where Poliquin got his figures from? 🤔
Anyhow, King goes on further to make some tempo recommendations like 804, 613, 421, and 313 but stipulates that these sorts of tempos are better for learning stability/control, general fitness objectives and the metabolic end of hypertrophy.
When he wrote the book in the late 90's early 2000's; Metabolic stress was believed to be one of the 3 main drivers of growth. We now know that metabolic stress has probably only a minor influence on growth, so I think it's safe to say you shouldn't bother using any of those tempos for growth – well ... maybe the 421 tempo ...
Why Slow Eccentrics Work
And maybe a slight pause at the bottom ...
Hopefully by now you realize that not all TUT is created equal, and thus we can effectively ignore it as a training variable. It's just not a good number to work with:
- Pausing at the top doesn't create much of a stimulus for growth because this is merely an isometric contraction → there is no active shortening or lengthening of the muscle fibres here, you need dynamic contractions
- Slow concentrics simply reduce the amount of weight you can tolerate, and thus reduce the stimulus for growth
- Pausing at the bottom for too long will also reduce the amount of weight you can handle, and probably reduce the stimulus for growth
- That's 3 of the 4 numbers used to calculate TUT, all impacting growth in a negative manner
However, this doesn't mean that tempo is a worthless concept. It's great for other training objectives. It means that adding up all the numbers in a tempo prescription doesn't give us anything of value to consider for growth. It doesn't represent the true mechanical stress applies to the muscle that yields growth.
→ Slow down the eccentric part of your lift (3-5 seconds) if growth is your objective.
This is really the only lifting tempo variable to date that appears to matter in the context of growth.
Well you're actually a lot stronger during the eccentric part of the lift, and motor recruitment ends up lower when yielding to a resistance you can concentrically lift. Yielding strength is greater than force generating strength, so fewer motor units are activated during the eccentric.
The maximum amount of force you can exert in an eccentric-only contraction is approximately 25-30% greater (depending on the lift) than in concentric-only contractions. Passive elements within the muscle permit this phenomenon, meaning less total muscle recruitment is required on the way down.
In other words, if you can bench press 100 lbs concentrically, you can probably lower about 125-130 lbs to your chest. You simply wouldn't be able to get it back up again without help.
85% of our one-repetition-maximum – 1RM, the maximum amount of weight you can concentrically lift in any given exercise – represents about a five-repetition-maximum (5RM) or a weight you can lift 5 times concentrically and dynamically.
This is actually only about 65% of our eccentric-only 1RM, when you lower that weight. And that's probably why slowing the eccentric down appears to have growth benefits. That and maybe some influence on the stretch reflex.
Since motor unit recruitment is lower during this part of the lift, you can't stimulate as much growth with the eccentric part of the lift via active mechanical tension.
In order to recruit a similar (albeit, probably not the same) number of motor units during the eccentric/lowering phase of the lift you can slow it down a bit and likely increase the tension ever so slightly. Enough to show statistically relevant improvements in hypertrophy in lab settings anyway.
However, in a twist of events, using eccentric overload approaches, like weight releasers, partner help on the concentric or 2Up-1Down lifting don't seem to improve complete hypertrophy outcomes. It merely shifts the type of hypertrophy that gets formed towards the tendons, likely because it reduces the still important concentric part of the lift. Less hypertrophy ends up near the muscle belly (where concentric lifting tends to shine).
I suspect the reason this is ineffective is that eccentric overload training usually results in the concentric being notably easier than it otherwise would. There's no easy or practical way to do multiple rep training that creates adequate overload on both the eccentric and concentric part of the lift.
- Weight releasers only work on rep #1.
- If you use spotters to help with the concentric so you can overload the eccentric they will almost always take more weight off the concentric than needed. Amounting to the concentric stress being less than it would be during regularly dynamic resistance training. Even if the eccentric reaches a higher level of stress the total effect on each rep balances out.
- 2Up-1Down lifting means the concentric is notably easier too because with two limbs the weight you're using is easy but also impossible with one limb.
In other words, dynamic contractions with slow eccentrics still seemingly require the concentric part of the lift to be maximally beneficial for hypertrophy.
The best case scenario for this so far is to slow down the eccentric part of the lift to roughly 3-5 seconds and lift concentrically as quickly and controlled as possible to maximize the load you can tolerate.
What You Should Do
It's simple. If growth is your goal, it's time to stop worrying about TUT. It's a meaningless number. A slow eccentric and maybe a slight pause at the bottom so you don't bounce out of the bottom will reduce the stretch reflex enough to matter. That should be all you need.
What I tell people with growth goals now is lower slow (3-5 seconds), have a controlled pause at the bottom (own the lift) and lift up controlled and fast. This amounts to tempos like:
|3 second Eccentrics||4 second Eccentrics||5 second Eccentrics|
*The jury is still out on a pause this long in my opinion, but all of these tempos will keep you under that 8 second maximum I mentioned earlier. I'd use all the other tempos before these ones.
Most trainees don't need to treat tempos so carefully, and merely attempting to control the lift on the way down, control the bottom and explode up is perfectly sound advice. You shouldn't need much more than that, until you're a very advanced trainee.
I still see TUT mentioned online frequently so hopefully I just burst a lot of bubbles.
The next time someone tells you all about TUT and how important it is, send them this article because it's not worth considering in the slightest as it currently stands.
Only the eccentric part seems to matter, and even then, I doubt it makes a significant difference in practice.
It's better to focus your attention on getting your sets to that point where the concentric visibly slows down, and the rest of the lift is under control. Those are likely the most effective or stimulating repetitions.