29 April 2020
Stretching Between Sets: Will it Make Me Grow More?
Bodybuilders are constantly on the lookout for any little thing that can give them an edge over the dreaded ever-slowing rate of gainz. There’s always a new supplement, training style, or one-cool-trick around the corner. While the grass always appears greener on the other side, it’s unlikely that anything new is going to swoop in…
Bodybuilders are constantly on the lookout for any little thing that can give them an edge over the dreaded ever-slowing rate of gainz. There’s always a new supplement, training style, or one-cool-trick around the corner. While the grass always appears greener on the other side, it’s unlikely that anything new is going to swoop in and revolutionize the game at this point. However, that doesn’t mean it isn’t worth looking into anything that could potentially help us build muscle just a little faster.
Stretching between sets isn’t a totally new concept by any means, but it is something that isn’t very well understood in the literature. It’s generally a good idea to think something through and see if it makes sense logically, anecdotally, and mechanistically, and then take a look at the applied science. So, first, let’s take a step back and think about this.
Would it make sense for stretching to enhance hypertrophy?
- The jacked guy at my gym swears by it.
Thanks for reading this article, I hope it’s been illuminating for you; enjoy the stretch-induced growth!
Just kidding. There’s a lot more to consider here, but we shouldn’t just dismiss anecdotes like this. Frankly, if a ton of jacked people all do the same thing… there’s probably something to it. And a lot of stuff that the bros were once ridiculed for is turning out to actually be solid advice. The fact that some bodybuilders have been talking about inter-set stretching for a while shouldn’t be ignored, but let’s dig deeper, shall we?
- Passive tension (stretching) has been shown to activate Akt, a key enzyme in cell metabolism and growth (19), although not as much as the active tension that occurs during eccentric contractions (18).
- Static stretching can occlude blood flow, preventing the clearance of metabolites built up during training. More metabolite buildup, while not a main driver of muscle hypertrophy, does help the process along (5). It should be noted however that this could potentially end up being a negative if used between sets, as it could cause so much fatigue to build up that it sabotages performance on later sets, reducing volume and total accumulated mechanical tension, and therefore reducing growth in the long term.
- Alternatively, some very light static stretching or dynamic stretching may promote blood flow and actually aid in the recovery process between sets, allowing for better performance and volume accrual. As a related aside, when comparing two conditions of 30 second rest between sets, where one group massaged the working muscle and one did nothing, there was a trend (although not statistically significant) for the massage condition to allow for better performance, probably due to improved blood flow and metabolite clearance (4). Importantly, though, a longer rest period still outperformed the massage condition, but if for whatever reason you’re limited to very short rest periods, doing something to promote blood flow might help.
- We know that stretching can cause muscle architecture changes in and of itself. Dating all the way back to 1980, there is evidence that hanging weights off of chickens’ wings caused muscle growth in as little as ten days (2,10), and some early-90’s work in quails showed it eventually could lead to hyperplasia as well (1). More recently, loaded stretch training (no contractions, just passively being stretched under load for 3 minutes per “set” with progressively more load over time) led to changes in muscle fascicle length and pennation angle and an increase in muscle thickness (22). An important note about these studies is only one (the most recent) was done on humans, and it used untrained subjects. We don’t know if loaded stretch training would make more advanced lifters grow. The latest review on the topic of stretch-induced changes to muscle concluded that stretch, especially externally-loaded or highly intense stretching, can cause architectural changes and potentially increase hypertrophy (16).
How about stretching when combined with lifting?
It’s common knowledge now that if you want to maximize muscle growth, you should probably prioritize training volume (within reason, of course). While there has been a small push recently on researching inter-set stretching, there is quite a bit of data out there on pre-workout stretching. A lot of it focuses on its effects on power and force output, but for the sake of this article I’m going to pass over that since it’s less important for hypertrophy specifically – if you can’t produce quite as much force or power, oh well, just use less weight and do a couple more reps, problem solved.
The research on pre-workout stretching and how it affects volume performance is… murky. A long-duration flexibility training session right before resistance training isn’t a great idea (15), nor is PNF stretching (3,9). Static stretching doesn’t seem to be as detrimental, but still not optimal. A few short bouts of static stretching to slight/mild discomfort has led to less reps performed on a single set to failure at various intensities in untrained men (9)and less bench press and leg press 10RM strength gains after 16 weeks in untrained women (21), although neither of those results were statistically significant (when compared to a no-stretching condition) so there’s no need to get too worked up.
More dramatically, a study with trained found large decreases in performance across the board for stretching before training (3), where lifters achieved 17.8% less total reps if they did ballistic stretching before training, or 20.8% less total reps if they did static stretching. That study didn’t specify the stretching intensity, but cited the NSCA Essentials of Strength and Conditioning textbook for the stretching methodology, so I’d hazard a guess that it was to mild/slight discomfort. It’s possible that this study found such a huge performance decrease because it measured total reps across multiple sets rather than in a single set; if the fatiguing effect of pre-workout stretching only really starts to manifest later in the workout, that could explain the difference. A 2016 study actually measured muscle CSA changes after 10 weeks with some intensepre-workout stretching (8/10 pain…no thank you). They had subjects train leg extensions with one leg stretching beforehand and one without, so they each acted as their own control – an awesome design for this sort of study. The leg that stretched before training ended up doing less reps per set, less total volume, and experienced less strength gain and increase in CSA (11). The stretching intensity is notable here, since to my knowledge, it’s the only study to use such intense stretching before training. Their reasoning may have been that they were trying to essentially “pre-fatigue” the muscle fibers before training, which could have led to more metabolite buildup and more growth (that’s pure speculation on my part), but what ended up happening was too much fatigue buildup, harming performance. To me, this is evidence that metabolic stress is a clear subordinate to mechanical tension for hypertrophy. Intense stretching would cause more metabolic stress than lighter stretching, and lo and behold, we see worse performance, and directly less growth, here than in the aforementioned studies using lighter stretching (they still hurt performance slightly, but it wasn’t statistically significant, unlike this one). If metabolic stress, not tension, was king, they probably would have seen different results in that study.
It sounds like pre-workout stretching is bad news for maximal growth, but there is also contrasting data showing that pre-workout static stretching does not effect growth in untrained men (12), nor does static or ballistic stretching effect growth in active, but not currently resistance training, men (7). I’ll say it again…it’s murky.
Zooming out, it appears that pre-workout stretching may have a negative-to-neutral effect on hypertrophy or rough proxies for it (like 10RM strength increases or total reps performed per set). Overall, it appears that some light stretching before a workout won’t kill your progress, but if you’re seeking optimality, it may be best to avoid it just to be safe. One good application of pre-workout stretching would be if you have some serious mobility restrictions – if you spend a couple minutes doing a few 30 second bouts of light stretching before you start lifting, you can acutely improve your range of motion and reap the benefits of full ROM training, which I hypothesize would outweigh (or at least balance out) the nonsignificant decrease in repetition performance that likely happens after stretching (even so, just add a set if you’re that worried about it).
Finally: What About Stretching Between Sets?
That brings us to the discussion of inter-set stretching. As discussed, there’s some logical reason to believe that it could be a beneficial practice, but the data we have on pre-workout stretching is much less sunny. But that doesn’t mean that stretching between sets instead can’t be different… only one way to find out.
From what I can gather, the first human study investigating inter-set stretching was published in 2010, looking at its effects on velocity (it decreased) and acceleration (no change) (8). Not exactly what we’re concerned with for hypertrophy, but it’s a start.
A little closer to the mark: a protocol involving 30 seconds of static stretching to mild discomfort during the 2-minute rest periods between sets over 8 weeks showed no difference in strength improvements, cortisol, or growth hormone as opposed to just sitting quietly for the rest period (23).
While it isn’t stretching exactly, foam rolling during rest periods also decreased rep performance per set (14). This could be due to the fact that subjects exerted as much force as possible onto the very firm foam roller, which probably caused quite a bit of metabolic stress and blood flow occlusion, similar to how intense stretching would. This makes me think that stretching (at least intense stretching) between sets might not be the best idea, but let’s keep digging.
Recently, more conflicting data was published. One study showed that 25 seconds of stretching to slight discomfort between sets caused higher subjective fatigue, less total work performed across all sets, and greater decrease in EMG across all sets, despite similar cell swelling and lactate buildup (17). On the other hand, 30 seconds of stretching to just before the point of pain/discomfort actually caused more growth than a non-stretching condition, but only in one of the sites that they measured (quad). (6). My hypothesis here is that the latter study was light enough of a stretch to simply promote more blood flow and metabolite clearance, aiding recovery between sets and improving overall performance, while the former study stretched hard enough to not get that benefit. But I guess that comes down to how you define “stopping before the point of pain/discomfort.” Finally, stretching the antagonist muscle (i.e. stretching the pecs between sets of rows) between sets may actually improverepetition performance across sets (13), and a protocol involving 4×8-12 to failure on calf raises with either 30 seconds rest or a 30 second loaded stretch between sets also showed more hypertrophy for the stretching group (20). However, this was a non-peer reviewed conference abstract, and so should be taken with a larger grain of salt than usual.
And there we have it. If you’re thinking that’s not very convincing in either direction, you’re right. Inter-set stretching of the agonist muscle can decrease bar velocity and could either hurt the potential for hypertrophy (by decreasing rep performance and increasing fatigue) or help for hypertrophy (notably, the study finding a benefit actually measured muscle growth, not just rep performance). There simply is not enough here to be able to draw any strong conclusions.
There’s a plethora of things I’d love to see done in this realm. We need some comparisons of different stretching intensities and durations between sets in order to pin down what inter-set stretching prescription has the best shot at enhancing muscle growth. Ideally, those studies would use trained subjects and take measures of subjective fatigue, muscle damage, rep performance across multiple sets of multiple exercises working the full body, and – of course – directly measure muscle growth over time.
TLDR and Practical Takeaways
The case for inter-set stretching to enhance hypertrophy is a bit of a paradox. On one hand, it could independently induce growth or generate more metabolic stress (intense stretching) or promote blood flow and recovery (light stretching), and either way I could see an argument for it being helpful. On the other hand, stretching is going to bring some fatigue, and if mechanical tension is the main thing we’re after anyway, and fatigue sabotages our ability to accrue the most tension, it doesn’t make sense to do.
We are far from having the definitive answer to this, but because both the logic and the research are unclear at this point, it’s probably safe to say that the effect won’t be large in either direction. If you want to give it a try, I’d stick with lighter intensity and experiment with stretching either the agonist or antagonist muscle, or maybe even both, between sets. For example, between sets of bench press, take a 2-minute rest and spend 25-30 seconds of that stretching the pecs, or the lats, or each. Maybe even throw in a loaded pec stretch to finish off after your last set…. who knows. For now, experimentation and note-taking are the best we have as we wait for more research to be done.
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