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So I was reading about hypertrophy, and heard that the optimal "time under tension" is about 45-60 seconds.

Elsewhere, I read that the optimal rep range for hypertrophy is 8-12 sets.

These two things sound contradictory to me. If I had to do 12 reps of, say, bicep curls, it would take me roughly 1-2 seconds per rep. That means that 12 reps would be 24 seconds. How does that correspond to 45-60 seconds of time under tension?

Rather, if I take 2 seconds per curl, I should be doing 30 reps in order to reach a time under tension of 60 seconds... and yet, I'm hearing nobody recommend 30 reps, they all usually recommend 12 at most.

What's going on here? Are my curls just too fast? Surely not, I think 2 seconds is a decent amount of time for a curl.

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    1-2 seconds is definitely on the quicker side of things. Are you skipping the eccentric? Intentionally working on fast and explosive concentrics? Jan 18 at 21:37
  • The intensity you train under is the important part. How regularly and closely you get to the point of failure. A high-intensity workout can be done in 30 - 45 minutes. It should be quality over quantity.
    – Neil Meyer
    Jan 19 at 14:10
  • if you are moving at 1-2 seconds per rep, you need to put more weight on the bar... What @NeilMeyer said is very true, the optimal rep count is such that you can't handle another rep at the end of each set. When you make it through all reps on each set, it's time to add more weight.
    – Z4-tier
    Jan 19 at 15:24
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The claim that there's an optimal time under tension for hypertrophy appears to have come from Charles Poliquin, who wrote in his 1997 book ("The Poliquin Principles") that 20-70 seconds of total time under tension per set is desirable for bodybuilders. No citation was given for this claim.

The idea that 8-12 reps is the optimal rep range for hypertrophy is an even older dogma that probably can't be attributed to any single author.

Both of these ideas are wrong.

Research has reliably shown than rep range does not matter for hypertrophy, as long as sets are done sufficiently close to failure and the reps are not so ridiculously high (more than 30 reps per set) that it starts turning into cardio1, 2. Sufficiently close to failure means that if you can lift 100kg for 15 reps, or 140kg for 5 reps, those two will have similar effects on hypertrophy, but lifting 100kg for 5 reps cannot be compared to lifting 140kg for 5 reps. Stronger By Science has a good write-up summarising this research.

Research has also shown that while time under tension does increase hypertrophy3, this is counteracted by the fact that you can lift less weight (or do fewer reps) with a deliberately slowed tempo than you could when lifting at a normal speed. The overall result is that lifting light weights for low reps with a slow tempo, lifting light weights for high reps with a fast tempo, and lifting heavy weights for low reps with a fast tempo all produce similar levels of hypertrophy4, again provided that you're training similarly close to failure in all cases.

Probably the only important thing to take away from this is that slow tempos or higher reps can act as a substitute for heavier weights for hypertrophy training, which may be useful to people who have limited access to equipment due to Covid-19 restrictions.

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  • Starting Strength makes a similar argument and is some of the best instruction for beginner progression on core lifts (looking past the usual criticisms on GOMAD and "it's meant for power lifters" (it is not, but Practical Programing is))
    – Z4-tier
    Jan 19 at 15:41
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In my opinion, two seconds is fast for a bicep curl.

We can split the bicep curl into four parts: concentric, top-hold, eccentric, and bottom-hold. When you look at timing for a bicep curl you can find these four numbers prescribed in seconds. For example, if I said to perform a 1-0-1-0 bicep curl, that's one second up, no pause at the top, one second down, no pause at the bottom, and the completes one rep. This is what it sounds like you're doing, about two seconds for one rep.

I think a solid bicep curl looks more like a 2-1-2-1, in other words, two seconds up, one-second pause at the top, two seconds down, and a one-second pause at the bottom. The totals six seconds per rep putting a 10 rep set at 60 s time-under-tension.

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  • Good advice, proper form in the decline portion of the exercise is important.
    – Neil Meyer
    Jan 19 at 14:12
  • I like this idea. Slow down the reps, and do less of them. But would it be okay to eliminate the 1 seconds pauses at top and bottom? I don't see how this is doing anything for my biceps, seems like it would just needlessly tire out my wrists?
    – Figoe
    Jan 19 at 20:22
  • This is, essentially, just an implementation of what David wrote. Borrowing his wording here, but, a deliberately slowed tempo with a decreased weight is just my preferred method of getting a set sufficiently close to failure. Pausing at the top usually gives me a great bicep pump and pausing at the bottom requires you to fully reset. If you're leaning forward slightly and keeping elbows by your side, pausing at the top works the biceps well. In the end, whatever you do to get to that 'sufficiently close to failure' point will drive the most growth.
    – C. Lange
    Jan 19 at 21:51

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