Are Long Rest Periods Out of Style?

Welcome to the Training Takeaway Newsletter by Data Driven Strength! Zac Robinson here.

The common narrative surrounding rest periods and muscle growth in the evidence based community has been - more is better. A hallmark study by Schoenfeld and colleagues is commonly cited to support this point, demonstrating superior muscle growth with 3 minutes versus 1 minute of inter-set rest. However, a recent preprint meta-analysis by Singer et al. challenges this narrative - suggesting that shorter rest periods are sufficient to optimize growth.

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​Study Overview:

This meta-analysis compared the available data in a few different ways. I am going to focus on the model that got the most press across social media, which their other analyses generally align with. In the model I’m referring to, the authors separated rest into 4 categories:

1. Short (≤ 60 seconds)
2. Intermediate (> 60 and <120 seconds)
3. Long (≥ 120 and <180 seconds)
4. Very Long (≥ 180 seconds)

Overall the model suggested no major differences between rest periods - and if you take the results at face value, rest periods of 60-120 seconds might be your best bet. With some of their other analyses, the authors suggested that rest periods ≤60 seconds may be a bit too short to optimize growth, particularly in the lower body, but the differences weren’t particularly large nor precise.

So to sum the results up, so long as you’re resting longer than 60 seconds, it's probably sufficient to maximize muscle group. That said, despite these results, I remain pretty unconvinced of the rest period literature at large. First and foremost, there are only 5 studies that use direct measures of muscle size. These are local measurements of the muscle like ultrasound, MRI, etc. which are less influenced by “noise” such as hydration status than something like a DXA scan. The authors did some secondary analyses that somewhat looked at these studies in isolation but omitted the two studies by Souza-Junior and colleagues. I believe this was done because the shorter rest group in these studies progressively decreased their rest intervals over the course of the training intervention, but I think looking at the impact these studies have on the pooled effect size could be important. Below I’ve re-analyzed the studies with direct measures of muscle size with and without the studies by Souza-Junior et al.

When including all of the studies with direct measures of muscle size, the effect span straddles zero with poor precision. Upon removing the Souza-Junior studies, the directionality of the point estimate flips and only 3 studies remain in the analysis. Conceptually, I think this demonstrates the uncertainty in this area, and that there just isn’t a ton of data to go off of. Considering that the best designed studies do tend to favor longer rest periods - I wouldn’t go out of my way to meaningfully cut my rest unnecessarily. Moreover, there are other aspects of the individual studies that are worth noting such as potentially uncontrolled proximities to failure. Some of these details are laid out nicely in an instagram post by Daniel Plotkin.​

All of this said, if you’re looking to either a) make your training sessions more time-efficient or b) trying to pack in more sets in a fixed training time, the potential downsides may be worth it. One could also appeal to the intensity technique research which seems to show similar growth using things like drop sets that use even shorter rest intervals. However, it's still unclear if an extra set or two is necessary to equate outcomes to longer rest intervals, potentially hinting at the theoretical downside.

The point here is that there is just a lot we don’t know. Personally, if I was to hedge my bets, I think there is probably something to be gained from longer rest periods - but that difference may very well be overshadowed by logistical upsides that shorter rests provide. Below is fitting the available data in the way that makes the most sense to me, treating the rest duration as a continuous variable. This would suggest noticeable improvements in muscle size as you move from very short to moderate rest periods but strongly diminishing returns thereafter. This comports well with what the authors reported but notice the absolutely massive uncertainty intervals and very little data - I think this one may just be a bit too early to form a strong opinion.

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From a practical perspective I prescribe rest intervals using the following 3 step process:

1. Rest as long as necessary to maintain performance
   • Multi joints ~3-5 min
   • Other ~1-3 min
2. Do you have time constraints?
   • If yes, decrease the ranges down by 1 minute
3. Autoregulate further based on training prescription
   • Closer to failure, higher rep, lower body - rest a bit longer
   • If the opposite, you can use slightly shorter rests

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