Ah yes, the age old decision. I mean, it’s not quite the HIIT/LISS question or the pancakes/waffles debate, but it's got to be up there.
Rest periods: short or long?
To find the answer, let’s do a little digging - starting with short rest periods.
Short rest periods allow you to complete more sets, as each round of work:rest takes less time than it would with longer rest periods. This will also likely make your sessions seem harder, as fatigue accumulates more quickly, and you continue to train through less and less recovery.
Say for example, you’re resting one minute between sets, and a set takes you 30 seconds. Here, you can pump through 6 sets in only 9 minutes. You’re probably going to feel pretty taxed, and that’s some serious set volume.
If you were resting 2.5 minutes between sets instead, you would only get through 3 sets in that time. Over an entire session, that’s a big difference.
Okay, chalk one up for short rest periods.
But if we dig a bit deeper, we see that long rest periods have a huge benefit, too. They lead to higher performance on a per set basis. You’ll be well rested and recovered for each new round of repetitions, so it makes sense that you’ll be able to do more.
More weight on the bar, more reps in the set, more sets for the session. All the hallmarks of traditional Progressive Overload.
So naturally we conclude long rest periods are better, right?
Maybe. Probably. But it’s not that simple.
In order to isolate the impact that rest periods have on hypertrophy (our goal in the gym, regardless of the goal with our physiques), we need to control for the confounding variables, such as total volume, effort, and total sets, which is no small feat. But that’s what the scientists have tried to do.
For example, Schoenfeld et al set up a study to match training effort, where people trained 3x/wk with a Full Body split, using a variety of staple exercises: Squat, Leg Press, Leg Extension, OHP, Lat Pulldown, Cable Row, and Bench.
One group rested 1m between sets, while the other group rested 3m between sets. Both groups trained to failure, with sets landing somewhere between 8-12 reps.
Naturally, with the shorter rest group, loads had to be continually decreased on later sets as fatigue accumulated quickly, whereas the longer rest group was better able to maintain performance at higher loads across multiple sets. So even though effort and total sets were controlled for, total volume was very different.
A great study on short versus long rest periods, but also just one example of many (like here and here) where concessions are made and controls are relaxed in order to move forward.
Leaving us to all wonder what’s best: quick and cruel, or long and brutal?
Turns out, to find any definitive answer to that question, we need to go in a slightly different direction, and attack the issue from an entirely new angle.
Fatigue.
Specifically, global and local fatigue.
When we get under the bar, our muscles get to work. But that’s not the only thing expending energy. Our system reserves start to dwindle, too.
And I don’t know about you, but I want the targeted muscle in question to be adequately stressed (local fatigue) before my gross motor units get too gassed to continue (global fatigue).
Not to mention, higher rep work (often times paired with shorter rest periods, you know, to tone and sculpt) can throw a wrench in these plans, just as the researchers showed here,
As lactate builds up in the blood from higher reps, and we’re never fully recovered from shorter rest periods, global fatigue can accumulate faster than local fatigue, causing us to shut down the set before enough local stress could be applied.
Result? The squats we’re doing don’t tax the quads enough before we have to stop, or the rows we’re doing don’t torch the lats enough before we have to stop.
You’re not progressively overloading because your system is smoked before you can really stress the targeted fibers. But you can’t just “train harder” because your total energy is the limiting factor, not the muscle strength itself.
OK - fair enough. You’ve convinced me to rest longer between sets.
But still, Jim, uh, bruh...I don’t have all day to train. I have a life to lead outside the squat rack, albeit a fairly uneventful and far less exciting one than AMRAP sets under the bar.
So how do I use all this information?
ACTION ITEMS
In a perfect world, we could rest 5 minutes between all sets: barbell squats and cable kickbacks. Hypertrophy would be optimized and happiness would be maximized.
Sadly though, most of us can’t do that. So here’s what we do.
First, if you’re in a season of life where you don’t have much time at all to train right now, then don’t worry about any of this, if you don’t want to. Just grip it and rip it. I’ve got 3 small children myself - no explanation necessary.
But second, under normal circumstances, your rest period length should coincide with the level of the global fatigue required of the movement:
HIGH Global Fatigue (S-B-D): 3-5 minutes (or more) between sets
MEDIUM Global Fatigue (Compound Movements): 2-3 minutes between sets
LOW Global Fatigue (Isolation Movements): 1-2 minutes between sets
Follow these protocols the next time you design your training split and build out your blocks.
Your muscle fibers will thank you.